2.5D Workflow Parameters


Minimum detections per cell

Minimum number of 3D points required for a grid cell during rasterization.

Default value(s): 2 or 3 for low overlap nadir scenarios, 1 otherwise

During DSM generation the dense 3D point clouds are rasterized/projected onto a regular 2D grid, where the cell size is determined by the GSD. This parameter controls the minimum number of 3D points which are required per raster cell, in order for a specific cell to be considered valid during rasterization.


Edge refinement

Apply additional sharpening of DSM edges.

Default value(s): enabled

This optional refinement method detects and artificially straightens edges in the DSM tiles, thereby improving the sharpness of e.g. building outlines. Furthermore, points registered on building facades can efficiently be filtered. The refined DSM edges will also have a positive effect on the quality of the edges in the subsequently generated True Ortho.

Without edge refinement

Edge refinement activated


Interpolation

Interpolate DSM's to fill holes.

CLI
-interp
-interpiwd

Default value(s): method = from lowest, radius = 30 pixels, minimal points = 4

The default interpolation method "from lowest" tries to extend low elevation parts/samples within the specified mask. This approach specifically tries to acquire sharp edges in the DSM's and consective  True Ortho's, by extending potential ground areas up to the roof edges, and thereby especially avoids just smoothing over these edges.  If less than the specified minimal points are found within the mask, no value will be interpolated and NaN will be assigned to the pixel.

The second interpolation method "IWD" employs the inverse weighted distance for weighing the pixel's values. Increasing the power parameter will lead to amplified weights in the mask's center, or damped weights in the mask's edges/corners, respectively. The number of minimal points in quadrant is similar to the minimal points, however, it will be evaluated for each quadrant (upper left, lower left, upper right, lower right) separately, so valid information from each quadrant are required for the interpolation.


TIFF world files

GUI: Save additional TFW files

CLI
-tfw / -no_tfw

The TIFF world files (*.tfw) store the georeferencing information next to the tiled TIFF files. Although the tiled TIFFs already contain this information in the GeoTIFF tags, some GIS softwares may not be able to read it directly from the images, hence the user has the option - active by default - to write the *.tfw files. This option can also be disabled.

By convention, the georeferencing coordinates point to the center of the top left pixel. Note that this information is consistent with the GeoTIFF tag, meaning there is an offset of half of pixel between the coordinates in the *.tfw file and the corresponding GeoTIFF tag.

Image Pyramids / Overviews

GUI: Write image pyramids in TIFF files

CLI
-image_pyramids / -no_image_pyramids

The image pyramids store the tiled TIFF images at lower resolution levels and are (by default) written into the layers of TIFF files.  These overviews are necessary to display efficiently extensive areas in GIS viewers, as well as when switching rapidly between different zoom levels and panning. Also in hierarchical processing through different resolutions of imagery, processes are faster as less data / lower resolutions have to be loaded for computations. The TIFF files containing these pyramids take roughly 33% more disk space than they would take without them. This option can be disabled in the GUI or CLI.


DSM Mesh output format

DSM Mesh output format.

Default value(s): osgb


Speckle Filter

Suppress noise by speckle filtering the DSM tiles.

Default value(s): size = 3, offset = 5

The size parameter denotes the maximum size for a patch to be considered a speckle. The offset threshold relates to the maximum disparity difference for a pixel to be included within the patch.

For the default parameters, a patch smaller than 3 pixels would be removed if it is more than 5 pixels in height different to its surroundings. It is thus very useful for filtering peaks.


Number of threads

Number of CPU threads used for parallel DSM generation.

Default value(s): 1

The DSM generation throughput is highly constrained by the system's I/O capabilities. We recommend to go for a higher number of threads only on system with a sufficiently high memory interface, e.g. like RAID 0.


Save optional outputs

The following list of optional (tiled) outputs are not needed for any subsequent processing step, and mainly intended for quality assessment purposes.

OptionDefaultDescription
Count images(error)Information about how many 3D points have been available per pixel for rasterization.
HIS image(error)Color coded height images.
Ortho image(tick)Colorized DSM TIFF tiles.
Interpolated ortho image(error)Colorized and interpolated DSM TIFF tiles.
DSM cloud(tick)Rasterized and colorized cloud tiles, corresponding to the DSM TIFF tiles.
Interpolated DSM image(tick)Colorized and interpolated DSM TIFF tiles.
Interpolated DSM cloud(tick)Rasterized, colorized and interpolated cloud tiles.
Binary mask image(error)Additional output tiles for quality assessment. → DSM QA: Binary Mask Image
Distance mask image(error)Additional output tiles for quality assessment. → DSM QA: Distance Mask Image
Model count image(error)Additional output tiles for quality assessment. → DSM QA: Model Count Image
Standard deviation image(error)Additional output tiles for quality assessment. → DSM QA: Standard Deviation Image