Assessing the Ability of Image Based Point Clouds Captured from a UAV to Measure the Terrain in the Presence of Canopy Cover
Abstract
:1. Introduction
1.1. UAS Image-Based Point Clouds in Forestry
1.2. Describing the Terrain
- using information contained in the point cloud to describe the terrain;
- using a description of the terrain derived from an alternate source; and
- extracting information from the point cloud without description of the a terrain.
1.3. Aims and Objectives
2. Materials and Methods
2.1. Study Area and Reference Data
2.2. Data Collection and Point Cloud Generation
2.3. Ground Filtering
2.4. DTM Creation
2.5. DTM Evaluation
2.6. Changes to Forest Characteristics
3. Results
3.1. Pointcloud Co-Registration
3.2. Manual Ground Identification and Terrain Modelling
3.3. Ground Filter Performance and Effects on Terrain Modelling
3.4. Effects on Vegetation Metrics
4. Discussion
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Site | Location | Vegetation Description | Terrain Description |
---|---|---|---|
EMP01 | 35°34′54″ S, 72°13′53″ W | Pine plantation with overlapping crowns, little understory but some significant woody debris and leaf litter. | Small change in gradient throughout plot. |
EMP02 | 35°35′55″ S, 72°15′02″ W | Disturbed remnant native forest, large areas of moderate to dense understory. | Little change in gradient across plot, local mounds around trees. |
ENS01 | 41°10′53″ S, 72°27′44″ W | Open, sparse canopy cover, little or no understory, area subject to recent landslide, vegetation generally in poor health | Flat, little change in gradient. |
ENS02 | 41°08′09″ S, 72°32′24″ W | Remnant native forest, complex canopy structure, many areas of moderate to dense understory and significant woody debris. | Steep slope, high frequency of terrain height change within plot. |
FRT01 | 41°07′28″ S, 73°01′44″ W | Remnant native forest,complex canopy cover with mid-layers, sparse understory, some woody debris. | Small change in gradient with some depressions spread throughout plot |
PNT01 | 35°27′36″ S, 72°17′42″ W | Burnt pine forest, consisting largely of charred stems, no understorey and minimal regrowth, woody debris or leaf litter. | Consistent change in gradient across slope. Some holes present, randomly distributed around plot. |
Method | Parameter | Purpose | Range min:step:max |
---|---|---|---|
Lasground | step (m) | Defines the size of the initial search area for ground points. | 0.01:0.01:1.0 |
spike (m) | The threshold at which spikes get removed. | 0.1:0.04:0.2 | |
offset (m) | The maximum offset in meters up to which points above the current ground estimate get included. | 0.01:0.01:0.5 | |
bulge (m) | defines how high coarse triangles in the initial TIN can rise above there neighbours | 0.1:0.04:0.21 | |
CSF | Grid Resolution (m) | The horizontal distance between two neighboring particles | 0.01:0.01:1.0 |
Rigidness | The rigidness of the cloth | 1:1:3 | |
Time step | controls the displacement of particles from gravity during each iteration | 0.1:0.1:1.5 | |
Class Threshold (m) | The distance from the final cloth to which points are attributed as ground | 0.01:0.01:0.10 |
Site Points | Control Points | Check | Nadir RMSE | Oblique RMSE | Composite RMSE | |||
---|---|---|---|---|---|---|---|---|
H (cm) | V (cm) | H (cm) | V (cm) | H (cm) | V (cm) | |||
PNT01 | 5 | 4 | 2.1 | 1.7 | 2.1 | 2.1 | 2.0 | 1.8 |
FRT01 | 4 | 2 | 3.2 | 1.2 | 3.9 | 1.5 | 3.7 | 1.2 |
EMP01 | 8 | 4 | 2.1 | 2.2 | 2.0 | 2.4 | 1.9 | 2.1 |
EMP02 | 6 | 4 | 2.3 | 1.4 | 2.5 | 1.7 | 0.7 | 2.1 |
ENS01 | 5 | 3 | 3.8 | 2.1 | 3.8 | 2.4 | 3.9 | 2.1 |
ENS02 | 5 | 2 | 1.4 | 1.6 | 1.4 | 2.1 | 1.5 | 1.2 |
Site | Image Network | Canopy Cover (%) | Ground (%) | RMSE (m) | ||
---|---|---|---|---|---|---|
nadir | 59 | 21 | 0.19 | 0.51 | 0.44 | |
EMP01 | oblique | 60 | 12 | 0.20 | 0.84 | 0.59 |
composite | 64 | 26 | 0.17 | 0.39 | 0.36 | |
nadir | 92 | 7 | 0.07 | 3.78 | 3.70 | |
EMP02 | oblique | 88 | 6 | 0.08 | 4.34 | 3.68 |
composite | 93 | 8 | 0.06 | 3.26 | 3.61 | |
nadir | 30 | 91 | 0.08 | 0.07 | 0.13 | |
ENS01 | oblique | 40 | 90 | 0.09 | 0.07 | 0.11 |
composite | 40 | 94 | 0.07 | 0.05 | 0.09 | |
nadir | 98 | 3 | 0.14 | 3.10 | 2.16 | |
ENS02 | oblique | 97 | 3 | 0.14 | 2.20 | 1.57 |
composite | 98 | 4 | 0.10 | 1.90 | 1.49 | |
nadir | 91 | 1 | 0.30 | 10.15 | 4.73 | |
FRT01 | oblique | 88 | 1 | 0.38 | 11.08 | 4.49 |
composite | 95 | 1 | 0.19 | 9.46 | 4.87 | |
nadir | 1 | 97 | 0.06 | 0.05 | 0.08 | |
PNT01 | oblique | 1 | 98 | 0.06 | 0.03 | 0.02 |
composite | 1 | 98 | 0.05 | 0.04 | 0.07 |
(a) Cloth Simulation Filter | ||||||||
Site | Technology | MCC | RMSE (m) | (m) | Optimum | |||
res | rigid | ts | ct | |||||
nadir | 0.87 | 0.30 | 0.47 | 0.05 | 2 | 0.50 | 0.06 | |
EMP01 | oblique | 0.83 | 0.64 | 0.79 | 0.05 | 3 | 0.50 | 0.06 |
composite | 0.88 | 0.28 | 0.38 | 0.05 | 3 | 0.50 | 0.06 | |
nadir | 0.72 | 0.36 | 3.20 | 0.05 | 3 | 0.30 | 0.04 | |
EMP02 | oblique | 0.72 | 0.47 | 3.73 | 0.05 | 3 | 0.30 | 0.04 |
composite | 0.68 | 0.27 | 2.90 | 0.05 | 3 | 0.30 | 0.04 | |
nadir | 0.95 | 0.13 | 0.07 | 0.05 | 1 | 0.70 | 0.06 | |
ENS01 | oblique | 0.96 | 0.08 | 0.07 | 0.05 | 1 | 0.70 | 0.06 |
composite | 0.96 | 0.07 | 0.05 | 0.05 | 1 | 0.70 | 0.06 | |
nadir | 0.47 | 0.42 | 2.34 | 0.05 | 3 | 0.30 | 0.06 | |
ENS02 | oblique | 0.49 | 0.45 | 1.67 | 0.05 | 3 | 0.30 | 0.06 |
composite | 0.52 | 0.38 | 1.48 | 0.05 | 3 | 0.30 | 0.06 | |
nadir | 0.69 | 0.29 | 11.28 | 0.25 | 1 | 0.30 | 0.06 | |
FRT01 | oblique | 0.61 | 0.41 | 10.89 | 0.25 | 3 | 0.30 | 0.06 |
composite | 0.61 | 0.55 | 9.28 | 0.25 | 3 | 0.30 | 0.06 | |
nadir | 0.79 | 0.06 | 0.04 | 0.05 | 2 | 0.50 | 0.06 | |
PNT01 | oblique | 0.72 | 0.06 | 0.03 | 0.05 | 1 | 0.50 | 0.06 |
composite | 0.80 | 0.05 | 0.04 | 0.05 | 1 | 0.50 | 0.06 | |
(b) lasground | ||||||||
Site | Technology | MCC | RMSE (m) | (m) | Optimum | |||
step | offset | bulge | spike | |||||
nadir | 0.89 | 0.20 | 0.44 | 0.05 | 0.41 | 0.05 | 0.17 | |
EMP01 | oblique | 0.82 | 2.43 | 0.68 | 0.15 | 0.41 | 0.01 | 0.17 |
composite | 0.89 | 0.19 | 0.31 | 0.10 | 0.41 | 0.01 | 0.17 | |
nadir | 0.66 | 1.31 | 3.43 | 0.03 | 0.41 | 0.01 | 0.09 | |
EMP02 | oblique | 0.61 | 2.36 | 3.72 | 0.04 | 0.41 | 0.01 | 0.09 |
composite | 0.62 | 0.72 | 2.92 | 0.03 | 0.41 | 0.01 | 0.09 | |
nadir | 0.95 | 0.46 | 0.07 | 0.10 | 0.31 | 0.09 | 0.17 | |
ENS01 | oblique | 0.95 | 0.08 | 0.06 | 0.10 | 0.31 | 0.13 | 0.17 |
composite | 0.95 | 0.08 | 0.05 | 0.10 | 0.31 | 0.09 | 0.17 | |
nadir | 0.35 | 4.73 | 2.50 | 0.04 | 0.41 | 0.01 | 0.13 | |
ENS02 | oblique | 0.44 | 3.74 | 1.75 | 0.03 | 0.41 | 0.01 | 0.13 |
composite | 0.45 | 3.25 | 1.60 | 0.03 | 0.41 | 0.01 | 0.13 | |
nadir | 0.22 | 13.48 | 8.62 | 0.05 | 0.41 | 0.05 | 0.13 | |
FRT01 | oblique | 0.15 | 15.02 | 10.61 | 0.05 | 0.41 | 0.09 | 0.13 |
composite | 0.25 | 11.83 | 8.60 | 0.05 | 0.41 | 0.05 | 0.13 | |
nadir | 0.76 | 0.06 | 0.05 | 0.01 | 0.31 | 0.01 | 0.09 | |
PNT01 | oblique | 0.67 | 0.06 | 0.03 | 0.01 | 0.41 | 0.01 | 0.17 |
composite | 0.76 | 0.05 | 0.04 | 0.01 | 0.31 | 0.01 | 0.09 |
Site | Image Set | Reference | Manual | CSF | LAStools | ||||
---|---|---|---|---|---|---|---|---|---|
Cover (%) | Height (m) | Cover (%) | Height (m) | Cover (%) | Height (m) | Cover (%) | Height (m) | ||
nadir | 61 | 14.57 | 61 | 14.36 | 61 | 14.30 | 61 | 14.41 | |
EMP01 | oblique | 64 | 13.76 | 64 | 13.57 | 64 | 13.43 | 63 | 12.99 |
composite | 68 | 14.42 | 68 | 14.22 | 68 | 14.17 | 68 | 14.24 | |
nadir | 90 | 8.01 | 90 | 8.01 | 90 | 7.78 | 89 | 7.35 | |
EMP02 | oblique | 86 | 8.10 | 86 | 8.11 | 86 | 7.79 | 84 | 6.78 |
composite | 91 | 8.01 | 91 | 8.02 | 91 | 7.84 | 90 | 7.75 | |
nadir | 38 | 9.85 | 38 | 9.86 | 38 | 9.84 | 38 | 9.83 | |
ENS01 | oblique | 50 | 11.08 | 50 | 11.07 | 50 | 11.07 | 50 | 11.08 |
composite | 50 | 11.05 | 50 | 11.04 | 50 | 11.04 | 50 | 11.03 | |
nadir | 92 | 18.88 | 97 | 18.83 | 97 | 18.58 | 95 | 16.46 | |
ENS02 | oblique | 91 | 18.85 | 96 | 18.80 | 96 | 18.55 | 96 | 17.20 |
composite | 93 | 18.86 | 98 | 18.80 | 97 | 18.65 | 97 | 17.66 | |
nadir | 89 | 21.62 | 90 | 21.57 | 90 | 21.56 | 83 | 8.77 | |
FRT01 | oblique | 89 | 21.57 | 90 | 21.41 | 90 | 21.75 | 81 | 8.36 |
composite | 94 | 21.60 | 94 | 21.64 | 90 | 22.14 | 92 | 10.45 | |
nadir | 1 | 7.05 | 1 | 7.07 | 1 | 7.07 | 1 | 7.07 | |
PNT01 | oblique | 1 | 7.56 | 1 | 7.66 | 1 | 7.64 | 1 | 7.65 |
composite | 1 | 7.59 | 1 | 7.70 | 1 | 7.68 | 1 | 7.68 |
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Wallace, L.; Bellman, C.; Hally, B.; Hernandez, J.; Jones, S.; Hillman, S. Assessing the Ability of Image Based Point Clouds Captured from a UAV to Measure the Terrain in the Presence of Canopy Cover. Forests 2019, 10, 284. https://doi.org/10.3390/f10030284
Wallace L, Bellman C, Hally B, Hernandez J, Jones S, Hillman S. Assessing the Ability of Image Based Point Clouds Captured from a UAV to Measure the Terrain in the Presence of Canopy Cover. Forests. 2019; 10(3):284. https://doi.org/10.3390/f10030284
Chicago/Turabian StyleWallace, Luke, Chris Bellman, Bryan Hally, Jaime Hernandez, Simon Jones, and Samuel Hillman. 2019. "Assessing the Ability of Image Based Point Clouds Captured from a UAV to Measure the Terrain in the Presence of Canopy Cover" Forests 10, no. 3: 284. https://doi.org/10.3390/f10030284