A Digital Terrain Model (DTM) is a topographic model used to represent the ground surface by digitally removing information about buildings, vegetation, and other features. In PIX4Dmatic, a DTM can be generated by following the instructions below.
Input
This processing option defines which input source is used for the DSM generation. The following options are available:
- Dense point cloud
- Depth point cloud (PIX4Dcatch projects)
- Depth & dense fusion (PIX4Dcatch projects)
Note: Multiple inputs can be selected for DTM generation. For all selected inputs, terrain classification must be applied before creating the DTM.
Resolution
Defines the spatial resolution used to generate the DSM. The default resolution is determined based on the calculated average Ground Sampling Distance (GSD) of the project.
- Resolution [units/px]: Defines the resolution of the DSM.
- Default: The resolution is 1 x GSD of the project.
- Custom: Allows to select any value for the resolution of the DSM.
Surface smoothing
The surface smoothing is applied to the generated DSM. When using Low values, the final DSM contains sharper features and edges. When using High values, the DSM is smoothed out.
- Surface smoothing (0 - 20, 12 - default): The radius of the median filter can be selected to determine the effect of DSM smoothing:
- 0: No smoothing is applied.
- Low (values closer to 1): Tries to preserve the orientation of the surface and to keep sharp features such as corners and edges of buildings.
- High (values closer to 20): Tries to smooth areas based on a larger surrounding area. Sharp edges will be smoothed out. Areas that are not very planar are smoothed and become planar.
Important: The DTM receives its input as the dense point cloud. If the dense point cloud is noisy, this will be directly reflected in the generated DTM. Make sure that the results of the Calibrate and Densify steps are optimal before generating the DTM.
Interpolation
The Interpolation parameters affect the completeness of the generated DTM:
- No interpolation. Only areas where the dense point cloud is generated are reconstructed in the DTM. Where the dense point cloud is not generated or is not dense enough, holes in the DTM appear.
- Interpolate holes. Holes in the DTM are filled based on neighboring data.
- Expand area. The DTM data is extended, attempting to cover the entire area that is visible from the (calibrated) cameras
Polygon-aware
Use a polygon to fill holes and flatten areas in the DSM.
Exports
To export the DTM, there are two methods to do it.
- From Content panel > Digital terrain model DTM > Export
- File > Export > DTM
The following export settings are available:
- Compression (LZW compression, Enabled - default): Defines the compression of the exported file.
- LZW compression - Enabled: No data is lost during the compression of the file and the .tiff is not degraded. This results in a smaller file size of the exported file.
- LZW compression - Disabled: No compression is used during the export. This results in a larger file size of the exported file.
- File Type (Single - default):
- Single: The image will be exported in a single file.
- Tiles (2048 px - default): The image will be exported in tiles with a predefined size of 1024 px, 2048 px, or 4096 px. The origin of the tiles is the top left corner of the project boundary.
- Image Scale (100%- default): Defines the scale of the exported file.
- 100%: The exported image will keep the original size.
- 50%: The exported image will be scaled to 50% of the original size.
- 25%: The exported image will be scaled to 25% of the original size.
Example: For a file with the original size of 10000 x 10000 pixels, the exported file with Image scale:
- 100%: 10000 x 10000 pixels.
- 50%: 5000 x 5000 pixels.
- 25%: 2500 x 2500 pixels.
- Save as...:
- Single: Specifies the path and the file name of the exported file.
- Tiles: Specifies the destination folder.