Technologies for the Preservation of Cultural Heritage—A Systematic Review of the Literature

: This work establishes the technological elements that have enabled the preservation, promotion, and dissemination of tangible and intangible cultural heritage in the period from 2018 to 2022. For this, a Systematic Literature Review (SLR) was conducted in the scientiﬁc databases Scopus, Science Direct, IEEE and Web of Science, which facilitated the identiﬁcation of 146 articles related to the topic. A quantitative and qualitative analysis of the journals, authors and topics was carried out, detailing the important variables required to establish the sought-out elements; for this purpose, the following were quantiﬁed in the papers: type, topic, categorization, country, and language; in the publications, the type of heritage chosen, the place of the heritage and the type of intervention were investigated. The number of publications reporting the use of some type of technology was also identiﬁed, ﬁnding that 70% of them show a technological approach to preserve cultural heritage, while 30% refer to other types of interventions. The technologies reported to be used the most are 3D digital technologies (44% of those showing technological applications), augmented reality or virtual reality, henceforth AR/VR (15%).


Introduction
Cultural heritage is a term made known in the middle of the 20th century mainly by entities interested in its protection, such as the United Nations Educational, Scientific and Cultural Organization, hereinafter UNESCO, which defines it in its document resulting from the 1972 Convention for the Protection of the World Cultural and Natural Heritage held in Paris, as all tangible and intangible cultural expressions [1,2].
Intangible cultural heritage is defined by UNESCO in the same document as the practices, representations, expressions, and knowledge that a country or region recognizes as part of its cultural heritage [1].
Globally, many countries have been concerned about preserving, disseminating and teaching new generations the cultural and intangible heritages they have in their territories, and found the use of information and communication technologies a very valuable tool to achieve that goal; these tools have been applied to publicize traditional places [3], ref. [4] as well as to teach the cultural richness of a country [5,6], disseminate traditional symbols specific to the culture of each region [7,8], teach about traditional music and dances [9,10], and as a method of digital protection of cultural and intangible heritage [11,12].
Different technologies have been used for the preservation of cultural heritage in the world, and in order to provide information on what technological strategies can be implemented to promote tangible and intangible cultural heritage, this article analyzes the references that, from a technological approach, have some direct relationship with the promotion, dissemination and appropriation of heritage in general, with the purpose of making available to those interested, support to adopt good practices in future research work on the subject.To

Related Works
The preservation of tangible and intangible cultural heritage is a commitment that many countries have assumed, as evidenced in the different studies related to the subject, such as the one presented in [14], where a systematic literature review on 3D Technologies used for the preservation of intangible cultural heritage is performed, articles indexed in Scopus, Web of Science and IEEE Xplore databases were analyzed, where it is established that the most used technologies to preserve tangible cultural heritage are: 3D visualization, 3D modeling, Augmented Reality, Virtual Reality and motion capture systems.
In [15], an SLR was conducted on the use of social networks as a platform to promote the public participation process of heritage conservation, 248 articles were analyzed, and it was concluded that social networks expand the range of options for people to have a say in the decision process of cultural heritage management.
Likewise, in [16], a study was conducted with the objective of identifying different alternatives to preserve cultural heritage in the context of smart cities.To achieve this, a literature review was conducted in Google Scholar and Portal Capes, where 80 articles were analyzed; the study concluded that 3D scanning techniques, Building Information Modeling (BIM), mobile applications for integrated management of asset preservation and sensors for the acquisition and analysis of data from collections in real time are the most applied technologies in the contexts of smart cities.
In turn, in [17], a study is conducted where the ethical implications of technological interventions to preserve cultural heritage are reviewed, providing a framework to review and apply ethical concepts to improve the processes of "planning, recording, processing and dissemination of digital workflows for heritage preservation".This implies an appropriate use of digital heritage recording.
In [18], a review focused on techniques and technologies used in materials that are used for the conservation of material cultural heritage that does not affect the health of people; in this sense, articles published in the Scopus database are reviewed, using the keywords "nanoparticles", "leaching" and "coatings", as a result, important information is provided showing the best options for leaching with nanoparticles estimation that can be applied in the conservation of cultural heritage, such as building facades and bronze sculptures, among others.
Reference [19] presents a systematic literature review that addresses intangible cultural heritage and its relationship with urban resilience by searching the Scopus and Web of Science databases, where 94 articles were analyzed.The study shows that there are links between both areas of study and considers that ICH should be integrated into urban resilience discourses.

Methodology
SLR constitutes a valuable tool for the construction of state-of-the-art research; it allows the creation of frameworks on which future research is supported [20]; reference [21] cited by [22] defines it as a review that strives to comprehensively identify, evaluate and synthesize all relevant studies on a given topic.
There are different methodologies for conducting SLR.In [20], one of three stages is proposed: the first constitutes the definition of search parameters (definition of hypotheses, construction and validation of search strings), the second stage refers to the identification, compilation and debugging of information from the articles consulted and the final stage is the analysis of results from the compiled information.
An SLR similar to this has been raised in [23], but its approach has been more theoretical; it consists of three stages, the first consists of a review of electronic articles that allows the collection of relevant data.The second stage consists of analyzing and synthesizing the collected documents and writing the research results.Finally, considerations and conclusions are formulated.
For the development of this work, the methodology applied in [20] was selected.For the definition of the search parameters, initially, a preliminary literature review was conducted in the field of research (consulting documents such as reviews and overviews), which allowed the identification of the hypotheses that mark the horizon of this study and, with them raise the research questions whose answer will be sought throughout this work.
The research questions that served as a guide to narrow the search parameters and conduct the SLR were: Q1-What types of interventions have enabled the conservation and preservation of the world's cultural heritage in the period 2018-2022?
Q2-What types of technologies have been used to conserve and preserve cultural heritage globally in the period 2018-2022?
Based on the above research questions, the key terms used for the construction of the search strings to be used in the SLR were identified (see Figure 1).
between both areas of study and considers that ICH should be integrated into urban resilience discourses.

Methodology
SLR constitutes a valuable tool for the construction of state-of-the-art research; it allows the creation of frameworks on which future research is supported [20]; reference [21] cited by [22] defines it as a review that strives to comprehensively identify, evaluate and synthesize all relevant studies on a given topic.
There are different methodologies for conducting SLR.In [20], one of three stages is proposed: the first constitutes the definition of search parameters (definition of hypotheses, construction and validation of search strings), the second stage refers to the identification, compilation and debugging of information from the articles consulted and the final stage is the analysis of results from the compiled information.
An SLR similar to this has been raised in [23], but its approach has been more theoretical; it consists of three stages, the first consists of a review of electronic articles that allows the collection of relevant data.The second stage consists of analyzing and synthesizing the collected documents and writing the research results.Finally, considerations and conclusions are formulated.
For the development of this work, the methodology applied in [20] was selected.For the definition of the search parameters, initially, a preliminary literature review was conducted in the field of research (consulting documents such as reviews and overviews), which allowed the identification of the hypotheses that mark the horizon of this study and, with them raise the research questions whose answer will be sought throughout this work.
The research questions that served as a guide to narrow the search parameters and conduct the SLR were: Q1-What types of interventions have enabled the conservation and preservation of the world's cultural heritage in the period 2018-2022?
Q2-What types of technologies have been used to conserve and preserve cultural heritage globally in the period 2018-2022?
Based on the above research questions, the key terms used for the construction of the search strings to be used in the SLR were identified (see Figure 1).
Figure 1 shows the scheme representing the search strings used, using as a particular focus in the thematic axes the words: "Cultural Heritage", "Conservation", "Preservation", "Technology".Figure 1 shows the scheme representing the search strings used, using as a particular focus in the thematic axes the words: "Cultural Heritage", "Conservation", "Preservation", "Technology".
The search strings constructed were validated in several specialized databases, which were selected from among the most recognized worldwide: Web of Science (WoS), Scopus, IEEE and Science Direct, which are related to the actuarial framework of the research that supports this article.
On the other hand, Table 1 presents the thematic axes considered and explains their combination strategies in the elaboration of the search strings.These combinations were used both in ascending and descending order.Thematic Axis 1 AND Thematic Axis 2 Link 2: Thematic Axis 1 AND Thematic Axis 3 Link 3: Thematic Axis 2 AND Thematic Axis 3 Link 4: Thematic Axis 1 AND Thematic Axis 2 AND Thematic Axis 3 Thematic axis 1 is directed towards the different types of heritage, while thematic axis 2 is centered on the main theme, which is the conservation and preservation of cultural heritage.Thematic axis 3 is more specific to the term's technology.The strategy consisted of combining, in the different possible ways, these three thematic axes by means of the logical connectors AND, and OR, limiting them in time to the period 2018-2022 to ensure the observation window of interest is maintained.
With these search strings, we proceeded to the second stage.In this stage, the different articles downloaded from the specialized databases were compiled and filtered, eliminating duplicate articles and those that did not directly obey the purpose of the research.
With the previous step, 142 articles were compiled, and with them, a data acquisition matrix was constructed that documented for each article the scientometric and technical variables that will be described in the following section.The final stage consisted of developing different analyses based on the quantitative and qualitative evaluation of the documented variables.
The technical variables used to document the bulk of the articles and especially those directly related to technologies applied to the conservation and preservation of cultural heritage, were: (1) Type of heritage, (2) Location of the heritage, and (3) Type of intervention, which corresponds to the processes developed to preserve and/or conserve the chosen heritage.At the same time, other more specific technical variables were documented considering the type of technology implemented.
The last stage of the research is the discussion of the results and conclusions.

Scientometric Analysis
For the study of the 146 publications found in the previous step, the following variables were used as scientometric variables: number of articles published by each database, year of publication, publication medium (proceedings, journal or book, in the case of a journal, the quartile is identified), it was also considered important to identify the countries of publication, both of the journal or event and of the authors (country of the first author) and finally the language of publication, all of them considering the subject of interest, filtered according to the search strings described above.
This analysis began with the quantification of the publications found according to the databases.The databases considered were IEEE, Scopus, Web of Science, ScienceDirect, Scopus-Web of Science, and Scopus-Web of Science-Science Direct, as shown in Figure 2. In Figure 2, it is identified that the scientific database with the highest number of publications found in the area of interest between 2018 and 2022 was Scopus, with 76 articles corresponding to 52% of the articles consulted.Scopus is one of the most accessed databases in the world; in addition, the focus of the articles published on this database is In Figure 2, it is identified that the scientific database with the highest number of publications found in the area of interest between 2018 and 2022 was Scopus, with 76 articles corresponding to 52% of the articles consulted.Scopus is one of the most accessed databases in the world; in addition, the focus of the articles published on this database is consistent with that of the present research.
From Figure 3, the subject studied shows a growing trend in terms of the number of publications per year since 2018; because this topic was of great interest to the academic community, it was still studied despite the global pandemic caused by the SARS-CoV-2 virus in the years 2020 and 2021.It is also evident that in the first months of 2022, publications on the subject continued to grow, which led us to believe that the trend would be maintained for the current year.In Figure 2, it is identified that the scientific database with the highest number of publications found in the area of interest between 2018 and 2022 was Scopus, with 76 articles corresponding to 52% of the articles consulted.Scopus is one of the most accessed databases in the world; in addition, the focus of the articles published on this database is consistent with that of the present research.
From Figure 3, the subject studied shows a growing trend in terms of the number of publications per year since 2018; because this topic was of great interest to the academic community, it was still studied despite the global pandemic caused by the SARS-CoV-2 virus in the years 2020 and 2021.It is also evident that in the first months of 2022, publications on the subject continued to grow, which led us to believe that the trend would be maintained for the current year.Regarding the number of publications according to the type of publication medium, the following were considered: proceedings, book chapters and those published in indexed journals.
Although only five book chapters were found, representing only 3% of the publications, it is clear from the results shown in Figure 4 that the topic is relevant for the scientific community in this area since, of the 146 publications analyzed, 100 (equivalent to 69%) have been published in indexed journals, which are usually specialized and have demanding evaluation systems, with more than one evaluator.Regarding the number of publications according to the type of publication medium, the following were considered: proceedings, book chapters and those published in indexed journals.
Although only five book chapters were found, representing only 3% of the publications, it is clear from the results shown in Figure 4 that the topic is relevant for the scientific community in this area since, of the 146 publications analyzed, 100 (equivalent to 69%) have been published in indexed journals, which are usually specialized and have demanding evaluation systems, with more than one evaluator.In Figure 2, it is identified that the scientific database with the highest number of publications found in the area of interest between 2018 and 2022 was Scopus, with 76 articles corresponding to 52% of the articles consulted.Scopus is one of the most accessed databases in the world; in addition, the focus of the articles published on this database is consistent with that of the present research.
From Figure 3, the subject studied shows a growing trend in terms of the number of publications per year since 2018; because this topic was of great interest to the academic community, it was still studied despite the global pandemic caused by the SARS-CoV-2 virus in the years 2020 and 2021.It is also evident that in the first months of 2022, publications on the subject continued to grow, which led us to believe that the trend would be maintained for the current year.Regarding the number of publications according to the type of publication medium, the following were considered: proceedings, book chapters and those published in indexed journals.
Although only five book chapters were found, representing only 3% of the publications, it is clear from the results shown in Figure 4 that the topic is relevant for the scientific community in this area since, of the 146 publications analyzed, 100 (equivalent to 69%) have been published in indexed journals, which are usually specialized and have demanding evaluation systems, with more than one evaluator.Normally, although the publications resulting from the presentation of papers at events are refereed, they are not categorized since they depend on the type of event, while books or book chapters go through the publisher's own evaluation systems.For this reason, in what follows, for the categorization of the publications consulted, only the number of publications found in specialized magazines or journals will be taken into account, which according to the graph shown in Figure 4, is 100.Of these, 90 journals were categorized, and 10 were not categorized, equivalent to 62% of the specialized publications consulted.
When analyzing these publications in journals that are categorized, it was found that 53 of them (corresponding to 59%) are categorized in Q1, 26 of them (corresponding to 29%) are categorized in Q2, 7 of them (corresponding to 8%) are in Q3, and the remaining 4 (corresponding to 4%) are in Q4. Figure 5 graphically shows the distribution described above, the categorization based on Scopus.
son, in what follows, for the categorization of the publications consulted, only the number of publications found in specialized magazines or journals will be taken into account, which according to the graph shown in Figure 4, is 100.Of these, 90 journals were categorized, and 10 were not categorized, equivalent to 62% of the specialized publications consulted.
When analyzing these publications in journals that are categorized, it was found that 53 of them (corresponding to 59%) are categorized in Q1, 26 of them (corresponding to 29%) are categorized in Q2, 7 of them (corresponding to 8%) are in Q3, and the remaining 4 (corresponding to 4%) are in Q4. Figure 5 graphically shows the distribution described above, the categorization based on Scopus.From the previous figure, it is very clear that the scientific community that publishes in this area has seen its work well valued since, due to its relevance and importance for the interested parties, it has been well categorized.The next scientometric variable analyzed was the country of origin of the first author of the articles.
Since many countries of origin were found for the first authors of the analyzed publications, it was decided to quantify the number of publications based on the countries with the largest number of authors.In Italy, there were 41 publications in the area of interest, equivalent to 28.1% of the total, followed by Spain with 15 publications (10.3%), and China with 14 publications (9.6%); the remaining countries with their respective number of publications and total percentage are shown in Figure 6: Algeria, Argentina, Austria, Bangladesh, Belgium, Canada, Colombia, Cyprus, Egypt, France, Germany, India, Iraq, Korea, Malaysia, Mexico, Pakistan, Shanghai, Slovakia, Slovenia, Sweden, Switzerland, Taiwan, Thailand, Ukraine, and the United Arab Emirates, whose individual contributions are minimal (but exist) and total 30 publications, which represent 20.5% of the publications studied.59% 29% 8% 4% Q1 Q2 Q3 Q4 From the previous figure, it is very clear that the scientific community that publishes in this area has seen its work well valued since, due to its relevance and importance for the interested parties, it has been well categorized.The next scientometric variable analyzed was the country of origin of the first author of the articles.
Since many countries of origin were found for the first authors of the analyzed publications, it was decided to quantify the number of publications based on the countries with the largest number of authors.In Italy, there were 41 publications in the area of interest, equivalent to 28.1% of the total, followed by Spain with 15 publications (10.3%), and China with 14 publications (9.6%); the remaining countries with their respective number of publications and total percentage are shown in Figure 6: Algeria, Argentina, Austria, Bangladesh, Belgium, Canada, Colombia, Cyprus, Egypt, France, Germany, India, Iraq, Korea, Malaysia, Mexico, Pakistan, Shanghai, Slovakia, Slovenia, Sweden, Switzerland, Taiwan, Thailand, Ukraine, and the United Arab Emirates, whose individual contributions are minimal (but exist) and total 30 publications, which represent 20.5% of the publications studied.Regarding the number of articles according to the country of the journal publishing it, it was found that Germany is the country of preference for publishing on this topic, with 34 publications corresponding to 24% of the total, followed by the United States with 33 publications (representing 23%); in this case, the conglomerate of 14 countries gathered in a single item add up to 28 publications, which corresponds to 20%, but now the countries are: Austria, Belgium, Brazil, China, Egypt, Spain, France, Italy, Jordan, Poland, Romania, Serbia, Turkey and Ukraine.
With respect to the language of publication, English is the predominant language, making up 95% of the articles published (139 articles), followed by Ukrainian with 1 article, representing 1%; the remaining 3% are distributed among other languages, as shown in Figure 7.  Regarding the number of articles according to the country of the journal publishing it, it was found that Germany is the country of preference for publishing on this topic, with 34 publications corresponding to 24% of the total, followed by the United States with 33 publications (representing 23%); in this case, the conglomerate of 14 countries gathered in a single item add up to 28 publications, which corresponds to 20%, but now the countries are: Austria, Belgium, Brazil, China, Egypt, Spain, France, Italy, Jordan, Poland, Romania, Serbia, Turkey and Ukraine.
With respect to the language of publication, English is the predominant language, making up 95% of the articles published (139 articles), followed by Ukrainian with 1 article, representing 1%; the remaining 3% are distributed among other languages, as shown in Figure 7.
it, it was found that Germany is the country of preference for publishing on this topic, with 34 publications corresponding to 24% of the total, followed by the United States with 33 publications (representing 23%); in this case, the conglomerate of 14 countries gathered in a single item add up to 28 publications, which corresponds to 20%, but now the countries are: Austria, Belgium, Brazil, China, Egypt, Spain, France, Italy, Jordan, Poland, Romania, Serbia, Turkey and Ukraine.
With respect to the language of publication, English is the predominant language, making up 95% of the articles published (139 articles), followed by Ukrainian with 1 article, representing 1%; the remaining 3% are distributed among other languages, as shown in Figure 7.The SLR also identified the journals with the largest number of publications on the topic of interest; this is divided into journals and Proceedings.It was found that the journal of Sustainability from Switzerland had 17 published articles, followed by five articles each in the following: the Swiss journal of Applied Sciences and the Journal of Cultural Heritage from France.The complete information on these publications can be found in Table 2.It should be clarified that not all articles are analyzed; only the journals with the highest number of articles are presented.The SLR also identified the journals with the largest number of publications on the topic of interest; this is divided into journals and Proceedings.It was found that the journal of Sustainability from Switzerland had 17 published articles, followed by five articles each in the following: the Swiss journal of Applied Sciences and the Journal of Cultural Heritage from France.The complete information on these publications can be found in Table 2.It should be clarified that not all articles are analyzed; only the journals with the highest number of articles are presented.

Technical Analysis
The technical aspects to consider when analyzing different investigations are the types of technologies applied to preserve tangible and intangible cultural heritage, in addition to establishing the type of heritage that is most intertwined with technological processes.
Bearing in mind that cultural heritage is divided into tangible and intangible, it should be noted that the primary interventions are carried out for tangible cultural heritage, such as churches, [24] museums [25], buildings [26], sculptures, paintings [27], among others, of which 131 articles (92%) correspond to tangible cultural heritage, as shown in Figure 8 [28].

Technical Analysis
The technical aspects to consider when analyzing different investigations are the types of technologies applied to preserve tangible and intangible cultural heritage, in addition to establishing the type of heritage that is most intertwined with technological processes.
Bearing in mind that cultural heritage is divided into tangible and intangible, it should be noted that the primary interventions are carried out for tangible cultural heritage, such as churches, [24] museums [25], buildings [26], sculptures, paintings [27], among others, of which 131 articles (92%) correspond to tangible cultural heritage, as shown in Figure 8 [28].In developing the SLR, the best options for applying technology to the preservation of the tangible and intangible cultural heritage of humanity were analyzed.
Regarding the types of intervention documented to preserve cultural heritage, of the 146 articles analyzed, 70%, 102 are related to the application of different types of technology to preserve cultural heritage, as shown in Table 3.Of the 101 articles related to technological intervention, the type of technology applied was reviewed, showing that 3D modeling (44%), virtual reality and augmented reality, hereinafter AR/VR (15%), are the types of technologies most used to preserve cultural heritage, as shown in Table 4.Other technologies include gamification, digital restoration, social networks, the use of information systems, and different web technologies, among other technologies applied to preserve cultural heritage in different parts of the world.
Table 5 shows the items that relate to 3D digital technologies.The heritage type item relates to whether it is natural, cultural or both; the heritage subtype relates to whether it is tangible, intangible, or both; and the final item is the specific heritage that has been chosen for the study.This same structure is used for the other types of applied technologies shown in Table 5.As shown in Table 5, the type of cultural heritage chosen by the application of 3D digital technologies is mostly cultural and tangible.Studies vary in the application of 3D digital technologies; some studies show this technology integrated with other types, as is the case for hyperspectral data for the estimation and evaluation of the degradation of materials used in heritage restoration by using geometric information point clouds and 3D meshes [37], the linking of the physical and digital world by combining Web-Gis, 3D and Internet of Things (IoT) technologies to preserve heritage buildings [69], proposals for virtual tours [57], simulations [63], which shows that it is the most used type of technology in preservation of cultural heritage especially material.
The chosen heritages vary in type and location; the Italian ones are the preferred choice, which corroborates what is shown in Figure 6.
From each of the articles related to the application of 3D digital technologies, the following technical variables were investigated: the Methodology implemented, which describes the steps used for the intervention; the Data Acquisition techniques, which establish the techniques used to obtain the information required for 3D modeling; the Data Acquisition Equipment, which corresponds to the different equipment used to obtain information; the Data Processing, which relates to the software tools used to process the information; and finally, the End Users, that relates to what type of users the intervention is directed at (i.e., Experts: are people, entities or institutions in charge of the protection of the cultural and natural heritage of humanity; Non-experts: are users and/or tourists who visit different heritages).
Review articles and those that do not specify the technical variables analyzed are excluded.The table with complete information is presented in the Appendix A (Table A1).
Photogrammetry and terrestrial laser scanning are the main techniques to acquire data for 3D digital technologies [27,30,37,41,45-48,55,60,65,66,70].Photogrammetry is mainly used due to the affordability of the devices (cameras) required, and in the case of laser scanning, together with suitable software, it is used mainly because of the speed at which it captures and processes data.
In [71], a comparison is made between these two software, highlighting the benefits of each one.They point out their preference for Autodesk because it has a free version for education, but this differs with what is shown in Table 6, where Agisoft Photoscan is used more despite being a proprietary software because it has no limits on the maximum amount of photographs to process, which allows quicker processing and excellent quality results.The end users of these interventions are mainly experts (78%), i.e., these types of interventions are carried out to obtain information that allows decisions to be made for the care and conservation of different heritages.

Virtual Reality/Augmented Reality (AR/VR)
As for the articles describing the use of AR/VR, they are presented in Table 6.
As in the previous case, the main chosen heritages are cultural and tangible, which confirms that they are the most protected by technological processes.
From the studies presented in Table 7, the following technical variables were analyzed: Data Acquisition Techniques, which establish the techniques used to obtain the required information; VR Software, which corresponds to the program used for the implementation of virtual or augmented reality; VR System, which corresponds to the level of immersion of the implementation (Immersive or non-immersive); Immersion Technology, which refers to the equipment used for the implementation of VR/AR; Data Acquisition Equipment, which relates to the different equipment used to obtain information; Data Processing, which relates to the software tools used to process the information; and finally, End Users, which relates to what type of users the intervention is aimed at (i.e., Experts: are people, entities or institutions in charge of the protection of the cultural and natural heritage of humanity, Non-experts: are users and/or tourists who visit the different heritages).Review articles and those that do not specify the technical variables analyzed are excluded.Table 7 shows the results.
Unlike the articles presented above (Tables 5 and A1), the application of AR/VR are more focused on non-expert users, i.e., they are mainly applications for visitors to interact virtually with the heritage, which contributes to its protection.
For these articles, photogrammetry stands out as a data acquisition technique [73,76,78,84] which establishes that for AR/VR applications, they prefer this technique to obtain the required images.
Around 77.78% of the applications are non-immersive in nature, 33% are accessed through an app for smartphones, an equal percentage are used through a high denomination computer, and the remaining 33% are accessed with both systems (App and high denomination PC).
The UE4 Unreal Engine is the software most used for visualization, among other reasons, because of the simplicity of its interaction, since you are not required to be an expert programmer to use it and also because of its fast rendering [73,78,80].
In [87], a study is presented where they develop an application that adapts the M.A.G.E.S. platform as AR to be used as VR in virtual museum applications.
It is very interesting how this application designs a device driver module to support all compatible VR headsets such as Oculus, HTC VIVE, Microsoft Mixed Reality and others.In addition, they use HoloToolK as API to integrate HoloLens to provide a Hologram service.
In [88], a study is presented for the creation of Cross/Augmented Reality applications for the Industrial Museum and Cultural Center in the region of Thessaloniki that can be replicated to showcase other types of cultural heritage.

IoT
Of the 146 articles analyzed, only four correspond to IoT technology, two applied in Italy, one in Spain and one in South Korea.The four articles correspond to tangible cultural heritage, as shown in Table 8.

Experts
From the studies presented in Table 8, the following technical variables were analyzed: Description of the Architecture, which corresponds to a brief synthesis of the IoT architecture presented in the article; Components of the architecture, which describes the elements that make up the architecture presented; Data Exchange, which describes how the information is handled within the architecture chosen; IoT System, which refers to the equipment used for the implementation of IoT technology; Protocols Used, which relates the different IoT protocols used in the implementation; and finally, End Users which relates to what type of users the intervention is aimed at (i.e., Experts: Are people, entities or institutions that are responsible for the protection of the cultural and natural heritage of humanity, Non-experts: are users and/or tourists who visit the different heritages).
Review articles and those that do not specify the technical variables analyzed are excluded.Table 9 shows the results.
As can be seen in Table 9, the platforms with IoT technologies designed for cultural heritage protection are very similar in their architecture; basically, they use nodes, gateways and a user interaction layer [89][90][91] The main IoT protocols used in terms of short-range networks are 5G and ZigBee [90,91].For long-range networks, the most widely used is LoRaWan [89,90].
Around 50% of the articles on IoT are addressed to expert users, and the other 50% to non-experts.

Conclusions
By means of a strict SLR based on the approach of carefully designed search chains to debug publications, 146 articles were filtered from which a description was made of the technological elements for the promotion, dissemination and appropriation of cultural heritage at a global level in a 2018-2022 observation window.For this review, several databases were carefully selected from among the most used for international publications, finding that most of the articles are published in specialized and indexed journals, duly categorized, most of them in Q1, in journals mostly from the USA and in English.
In response to the questions posed regarding the type of intervention that has enabled the conservation and preservation of the cultural heritage of humanity in the period between 2018-2022, Table 3 shows that cultural heritage intervention has been achieved from different approaches, where it stands out that the main interventions are technological (70%) and architectural (6%).
Regarding the second question, the types of technologies that have been used to conserve and preserve cultural heritage globally in the period between 2018-2022 are mainly 3D digital technologies (encompassing 3D modeling, 3D Scanning, 3D Visualization), AR/VR (immersive and non-immersive) and IoT platform configuration.
The use of technology to preserve tangible and intangible cultural heritage constitutes smart cultural heritage management, a term widely used worldwide.
From the above, it can be concluded that the technological elements and resources available today allow the inclusion of technology as a tool to contribute to the preservation of cultural elements and intangible heritage.

Future Work
Based on the results, recommendations for future research are made.The first relates to the application of technology for the preservation and dissemination processes of intangible cultural heritage, as in the case of Colombian vallenato and Spanish flamenco.
The second recommendation consists of the deepening of educational processes implemented to preserve intangible cultural heritage.
Considering Figure 8, 92% of the implementation of technological solutions is mainly in tangible heritage; it would be interesting to deepen the implementation of technology for the protection of intangible heritage in general.Making a replica of Tutankhamun's tomb using a high-resolution two-and three-dimensional capture of the images of the original tomb.The print of the images was vacuum filled on a base of milled and molten resin to be assimilated to the surface contours of the original wall.

Appendix A
Laser scanning and photogrammetry Does not specify Does not specify Non-experts [67] Recopilation and data processing, Identification of historical details, Constructing of parametric historical objects and mapping of parametric objects in scanning data to produce complete engineering orthographic drawings and 3D models.

Laser scanning HBIM
Artificial Intelligence "AI" sensors and cameras HBIM and IoT tools Experts

Figure 1 .
Figure 1.Diagram of the search chains built for the bibliographic compilation referring to the subject under study.The search strings constructed were validated in several specialized databases, which were selected from among the most recognized worldwide: Web of Science (WoS), Scopus, IEEE and Science Direct, which are related to the actuarial framework of the research that supports this article.

Figure 1 .
Figure 1.Diagram of the search chains built for the bibliographic compilation referring to the subject under study.

Figure 3 .
Figure 3. Number of publications: vs: Year of publication.

Figure 4 .
Figure 4. Number of publications: vs: Publication media type.

Figure 3 .
Figure 3. Number of publications: vs: Year of publication.

Figure 3 .
Figure 3. Number of publications: vs: Year of publication.

Figure 4 .
Figure 4. Number of publications: vs: Publication media type.

Figure 4 .
Figure 4. Number of publications: vs: Publication media type.

Figure 6 .
Figure 6.Number of publications: vs: country of the first author.

Figure 6 .
Figure 6.Number of publications: vs: country of the first author.

Figure 7 .
Figure 7. Number of publications according to the language of the paper.

Figure 7 .
Figure 7. Number of publications according to the language of the paper.

Figure 8 .
Figure 8. Number of publications according to the type of cultural heritage.In developing the SLR, the best options for applying technology to the preservation of the tangible and intangible cultural heritage of humanity were analyzed.

Figure 8 .
Figure 8. Number of publications according to the type of cultural heritage.

Table 1 .
Thematic axes and combination strategies used in the review.

Table 2 .
Journals with more publications.

Table 2 .
Journals with more publications.

Table 3 .
Type of intervention.

Table 4 .
Types of Technologies.

Table 5 .
Articles on 3D digital technologies.

Table 9 .
Technical aspects of IoT articles.

Table A1 .
Technical aspects of 3D digital technologies articles.