r.surf.contour(1grass) GRASS GIS User's Manual r.surf.contour(1grass)
NAME
r.surf.contour - Generates surface raster map from rasterized con-
tours.
KEYWORDS
raster, surface, interpolation
SYNOPSIS
r.surf.contour
r.surf.contour --help
r.surf.contour input=name output=name [--overwrite] [--help] [--ver-
bose] [--quiet] [--ui]
Flags:
--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=name [required]
Name of input raster map containing contours
output=name [required]
Name for output raster map
DESCRIPTION
r.surf.contour creates a raster elevation map from a rasterized contour
map. Elevation values are determined using procedures similar to a
manual methods. To determine the elevation of a point on a contour
map, an individual might interpolate its value from those of the two
nearest contour lines (uphill and downhill).
r.surf.contour works in a similar way. Initially, a vector map of the
contour lines is made with the elevation of each line as an attribute.
When the program v.to.rast is run on the vector map, continuous "lines"
of rasters containing the contour line values will be the input for
r.surf.contour. For each cell in the input map, either the cell is a
contour line cell (which is given that value), or a flood fill is gen-
erated from that spot until the fill comes to two unique values. So the
r.surf.contour algorithm linearly interpolates between contour lines.
The flood fill is not allowed to cross over the rasterized contour
lines, thus ensuring that an uphill and downhill contour value will be
the two values chosen. r.surf.contour interpolates from the uphill and
downhill values by the true distance.
Parameters:
input=name
Name of an existing raster map that contains a set of initial cate-
gory values (i.e., some cells contain known elevation values (de-
noting contours) while the rest contain NULL values).
output=name
Name to be assigned to new output raster map that represents a
smooth (e.g., elevation) surface generated from the known category
values in the input raster map layer.
An existing MASK raster map is respected for both reading input and
writing output.
NOTES
r.surf.contour works well under the following circumstances: 1) the
contour lines extend to the the edge of the current region, 2) the pro-
gram is run at the same resolution as that of the input map, 3) there
are no disjointed contour lines, and 4) no spot elevation data BETWEEN
contour lines exist. Spot elevations at the tops of hills and the bot-
toms of depressions, on the other hand, improve the output greatly.
Violating these constraints will cause non-intuitive anomalies to ap-
pear in the output map. Run r.slope.aspect
on r.surf.contour results to locate potential anomalies.
The running of r.surf.contour is very sensitive to the resolution of
rasterized vector map. If multiple contour lines go through the same
raster, slight anomalies may occur. The speed of r.surf.contour is de-
pendent on how far "apart" the contour lines are from each other (as
measured in raster cells). Since a flood fill algorithm is used, the
program’s running time will grow exponentially with the distance be-
tween contour lines.
EXAMPLE
Example to create contour lines from elevation model, then recreating
DEM from these contour lines along with differences analysis (North
Carolina sample data set):
g.region raster=elevation -p
# get minimum elevation value
r.univar elevation
# generate vector contour lines
r.contour input=elevation output=contours_5m step=5 minlevel=50
# rasterize contour lines
v.info -c contours_5m
v.to.rast input=contours_5m output=contours_5m use=attr attribute_column=level
# generate DEM from rasterized contour lines
r.surf.contour input=contours_5m output=elevation_from_cont5m
# calculate difference map
r.mapcalc "diff = elevation - elevation_from_cont5m"
r.colors diff color=differences
# analyze differences statistically
r.univar diff
SEE ALSO
r.mapcalc, r.slope.aspect, r.surf.idw, wxGUI vector digitizer,
v.surf.idw, v.surf.rst, v.to.rast
Overview: Interpolation and Resampling in GRASS GIS
AUTHOR
Chuck Ehlschlaeger, U.S. Army Construction Engineering Research Labora-
tory
SOURCE CODE
Available at: r.surf.contour source code (history)
Accessed: unknown
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GRASS 7.8.7 r.surf.contour(1grass)
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