r.object.thickness - GRASS GIS manual

NAME

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

KEYWORDS

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] [transects=name] [itransects=name] [csvfilename=name] [--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
transects=name: Vector map of complete transects
itransects=name: Vector map of inner transects
csvfilename=name: CSV output file

DESCRIPTION
PARAMETERS
EXAMPLE
SEE ALSO
AUTHORS

DESCRIPTION

r.object.thickness evaluates 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 primarly used to estimate the neighborhood window size for filters, such as those used by r.neighbors and r.fill.category.

Object thickness is evaluated by creating transects along the median lines of the raster objects, clipping them with object themselves and evaluating their lengths.

Optionally, r.object.thickness can save a CSV file containing the complete list of the lenghts of the parts of all created transects inside the objects. It is possible to save a maps containing the median lines of the objects, in both raster and vector format, a vector map containing the transects and a vector map containing the clipped transects.

The v.transects addon must be installed to run this module.

PARAMETERS

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

The expected maximum lentgth 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 secton of the biggest object. The module issues a warning if the maximum evaluated thickness is less than or equal to the expected maximum: in this 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.

Transects 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 abount 1/50 of the expected maximum size, but the minimum value can change. If the the transects spacing value is too low no transect is created and no thickness can be evaluated: in this case the module issues an error and stops.

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

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 lenghts 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 thickness of the water bodies in the landuse map in the North Carolina sample dataset location 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

AUTHORS

Paolo Zatelli, DICAM, University of Trento, Italy.

SOURCE CODE

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