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NAME

r.object.thickness - Evaluates minimum, maximum and mean thickness of objects of a given category on a raster map.

KEYWORDS

raster, algebra, size, clumps

SYNOPSIS

r.object.thickness
r.object.thickness --help
r.object.thickness input=name category=integer tsize=float tspace=float resolutiondir=string [rmedian=name] [vmedian=name] [vcategories=name] [transects=name] [itransects=name] [csvfilename=name] [metric=string] [transect_perpendicular=string] [iterations=integer] [--overwrite] [--help] [--verbose] [--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
category=integer [required]
Category to evaluate
tsize=float [required]
Expected maximum size in map units
Default: 100
tspace=float [required]
Transect spacing in map units
Default: 2
resolutiondir=string [required]
Resolution for output in pixels
Options: N-S, E-W
Default: N-S
rmedian=name
Raster map of median lines
vmedian=name
Vector map of median lines
vcategories=name
Vector map of areas
transects=name
Vector map of complete transects
itransects=name
Vector map of inner transects
csvfilename=name
CSV output file
metric=string
Determines how transect spacing is measured
Options: straight, along
Default: straight
straight: Straight distance between transect points
along: Distance along the line (see v.transect for details)
transect_perpendicular=string
Determines which line is the transect perpendicular to
Options: trend, line
Default: trend
trend: Perpendicular to the line connecting transect points. line
iterations=integer
Maximum number of iterations (used during thinning)
Default: 200

Table of contents

DESCRIPTION

r.object.thickness evaluates the minimum, maximum, and mean thickness of objects of a given category on a raster map. The thickness is reported both in map units and pixels. The module is primarily used to estimate the neighborhood window size for filters, such as those used by r.neighbors) and r.fill.category.html.

Another use case is to estimate the width of small landscape elements (SLE), e.g., to complement statistics computed by r.object.geometry

Object thickness is evaluated by creating transects along the median lines of the raster objects, clipping them with objects themselves, and evaluating their lengths. This is done using the v.transects addon, which must therefore be installed to run this module.

Optionally, r.object.thickness can save a CSV file containing the complete list of the lengths of the parts of all created transects inside the objects. It is possible to save a vector map containing the transects, a vector map containing the clipped transects and maps containing the median lines of the objects, in both raster and vector format. The attribute table of the latter contains the average, minimum, and maximum widths of the transects within the objects.

PARAMETERS

The user indicates the category of the objects whose thickness must be evaluated, and indicating the expected maximum length of the transects and their spacing.

The expected maximum length of the transects is used to create the transects before clipping them with the raster objects. It must be chosen large enough to contain the longer cross section of the biggest object. The module issues a warning if the maximum evaluated thickness is less than or equal to the expected maximum: in that case, at least one transect has not been clipped because it does not intersect the object boundary. Therefore, the expected maximum size parameter must be raised.

Transect spacing controls the distance between transects along the median line. It must be chosen so that at least one transect is created on each median line. Smaller values can provide slightly more accurate results but require more processing time. As a rule of thumb, a good starting point is setting transects spacing around 1/50 of the expected maximum size, but the minimum value can change. If the transects spacing value is too low, no transect is created and no thickness can be evaluated: in that case, the module issues an error and stops.

It is possible to choose the direction (N-S or E-W) of the region resolution used to convert the estimated lengths in pixels. The choice is irrelevant for regions with square cells.

The way the transect spacing is measured and whether the transects are generated , perpendicular to the input line or the line connecting the transect points, can be set by respectively the metric and transect_perpendicular parameters. See the manual page of [v.transects](v.transects.html) for details.

Optional maps containing the median lines of the objects, in both raster and vector format, the vector map containing the transects, and the vector map containing the clipped transects are created only if a name is provided for them. In the same way, a CSV file containing the complete list of the lengths of the parts of all created transects inside the objects is also created only if a file name is given.

EXAMPLE

In this example, the width of the water bodies in the landuse map in the North Carolina sample dataset is evaluated:
# set the region on the landuse map
g.region rast=landuse@PERMANENT
# evaluate the thickness of water bodies (categoy 6) in the landuse map
# create a vector map containing the median lines called median
# create a vector map containing the transects inside the water bodies called transects_in
r.object.thickness input=landuse@PERMANENT category=6 tsize=4000 tspace=100 vmedian=median itransects=transects_in
outputs
Thickness in map units:
min = 1.525433
max = 2962.446155
mean = 301.059197

Thickness in pixels:
min = 0.053524
max = 103.945479
mean = 10.563481

SEE ALSO

r.neighbors, r.reclass.area, v.transects,

AUTHOR

Paolo Zatelli, DICAM, University of Trento, Italy (original script).
Paulo van Breugel, HAS green academy (add stats to generated vector layers).

SOURCE CODE

Available at: r.object.thickness source code (history)

Latest change: Friday Jun 06 23:38:55 2025 in commit: 1ff8ddee6a01630b69dba1cbc92c31c588b10b86


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