Search Results (2)

Along with the development of three-dimensional computer graphics, methods of collecting and making 3D spatial data available became a significant issue covering the interoperability of data derived from multiple sources. Between 2006 and 2008, the Open Geospatial Consortium designed a CityGML model as a proposal for a uniform classification, graphic representation, construction, and storage of 3D objects. A considerable part of three-dimensional visualisations, now gaining popularity, make use of solutions based on the CityGML standard, with which they are compatible to various degrees. The survey involved a comprehensive analysis of sixteen generally accessible 3D geoportals of cities in Europe, Asia, and North America in terms of their broad-sense functionality as well as technical and thematic compatibility with the assumptions of CityGML standards. The level of realisation of various features related to the provided spatial data services was evaluated, taking into account elements that the present-day world literature deems to be particularly desirable. The analysis resulted in an elaborate ranking of websites according to 21 criteria. The most common objects and features of the analysed geoportals were also detailed. In addition, the authors presented several solutions to improve the quality of three-dimensional geoportals of cities by implementing external data from various sources. Full article

This research aims to protect Digital Elevation Model (DEM) data from piracy or counterfeiting. An invisible watermark inserted into the data, which will not considerably change the data value, is necessary. The proposed method involves the use of the two-dimensional discrete cosine transform (2D DCT), a combination of 2D DCT and discrete wavelet transform (DWT), and two-dimensional discrete Fourier transform (2D DFT) in the frequency domain. The data used include a National DEM file downloaded from the geoportal of the Geospatial Information Agency (Badan Informasi Geospasial—BIG). Three files represent mountainous, lowland/urban, and coastal areas. An “attack” is also conducted on the watermarked DEM by cropping. The results indicate that the watermarked DEM is well recognized. The watermark can be read 100% for 2D DCT, while that for 2D DFT can be read 90.50%. The distortion value of the elevation data under the DCT technique demonstrates the smallest maximum value of 0.1 m compared with 4.5 and 1.1 m for 2D DFT and 2D DCT–DWT. Meanwhile, the height difference (Max Delta), the peak signal-to-noise ratio, and the root mean squared error (RMSE) are highest in mountainous, lowland, and coastal areas, respectively. Overall, the 2D DCT is also superior to the 2D DFT and the2D DCT–DWT. Although only one can recognize the nine watermarks inserted on each sheet, DEMs attacked by the cropping process can still be identified. However, this finding can sufficiently confirm that DEMs belong to BIG. Full article