r.patch.smooth - GRASS GIS manual

NAME

r.patch.smooth - Module for patching rasters with smoothing along edges

KEYWORDS

SYNOPSIS

r.patch.smooth

r.patch.smooth --help

r.patch.smooth [-s] input_a=name input_b=name output=name [overlap=name] [blend_mask=string] [smooth_dist=float] [transition_angle=float] [parallel_smoothing=integer] [difference_reach=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-s: Use spatially variable overlap
--overwrite: Allow output files to overwrite existing files
--help: Print usage summary
--verbose: Verbose module output
--quiet: Quiet module output
--ui: Force launching GUI dialog

Parameters:

input_a=name [required]: Name for input raster map A; Name of input raster map
input_b=name [required]: Name for input raster map B; Name of input raster map
output=name [required]: Name for output raster map
overlap=name: Name for raster map of spatially variable overlap; Name for output raster map
blend_mask=string: Raster containing edge of raster A which is not to be blended; Useful when raster A has common edge with raster B
smooth_dist=float: Smoothing distance in map units
transition_angle=float: Angle of transition for spatially variable overlap; Recommended values between 1 and 5 degrees
parallel_smoothing=integer: Size of smoothing window for smoothing edges of spatially variable overlap zone; Small value results in more rugged shape of the overlap zone, large values result in spatially non-variable overlap zone. Requires odd values.; Options: 3-99; Default: 9
difference_reach=integer: Look for maximum difference between surfaces in surrounding n cells from the edge; Recommended values between 3 and 9; Options: 2-100; Default: 3

DESCRIPTION
SEE ALSO
REFERENCES
AUTHOR

DESCRIPTION

Module fuses rasters representing elevation together by patching them and smoothing values along edges using either fixed or spatially variable overlap width. Spatially variable overlap width is given by the difference along the edge between the two rasters. Higher difference results in larger overlap width to smooth the transition.

r.patch.smooth can be used, for example, for updating older, lower resolution DEM (input_b) with newer, higher resolution DEM (input_a). Note that both DEMs must be aligned and have the same resolution. Smoothing uses weighted averaging on the overlap of the rasters. r.patch.smooth supports 2 types of smoothing. The default one is simpler and uses fixed overlap width defined in smooth_dist. Since the differences along the seam line can vary, the second option uses spatially variable overlap width and can be activated with flag -s. The width is then computed based on the elevation differences along the edge and transition angle transition_angle controlling the steepness of the transition. If option overlap is specified, a map representing the spatially variable overlap is created and can be used for inspecting the fusion results.

Difference between fixed overlap width and spatially variable overlap.

For spatially variable overlap, options parallel_smoothing and difference_reach can be specified. Option parallel_smoothing smoothes the overlap zone in direction parallel to the edge. Option difference_reach enables to increase the sensitivity to higher differences on the edges by taking maximum difference values in the cells close to edges.

Effect of parallel_smoothing option shown on overlap zone (created by specifying overlap option). Image A shows result with value 3 and B with value 9.

Option blend_mask (experimental) can be used to specify which edges of the input_a DEM should be excluded from the blending. This is useful when DEMs A and B have identical edges (on the coast, for example) and we want to preserve only A (not blend it with B along the coast). The blend_mask raster can be created by digitizing area approximately around the excluded edges, so that the edge of DEM A is inside the areas and the rest are NULLs. This option requires more testing.

REFERENCES

Anna Petrasova, Helena Mitasova, Vaclav Petras, Justyna Jeziorska. Fusion of high-resolution DEMs for water flow modeling (2017). Open Geospatial Data, Software and Standards. 2: 6. DOI: 10.1186/s40965-017-0019-2

AUTHOR

Anna Petrasova, NCSU OSGeoREL

SOURCE CODE

Available at: r.patch.smooth source code (history)