NAME
v.curvature - Calculate curvature. With segment option it reads from standard input:
segment_id line_category from to
and writes to standard output:
segment_id average_curvature average_radius
If a segment given runs outside the line, it is cut. If more lines with the same category are found, curvature is not calculated and warning is printed.
KEYWORDS
vector, segment, curvature
SYNOPSIS
v.curvature
v.curvature help
v.curvature [-a] map=name [type=string[,string,...]] [layer=integer] [option=string] [--verbose] [--quiet]
Flags:
- -a
- Calculate average from absolute values (if not used, segment over 2 successive contrary curves can result in curvature near 0).
- --verbose
- Verbose module output
- --quiet
- Quiet module output
Parameters:
- map=name
- Name of input vector map
- type=string[,string,...]
- Feature type
- Options: line,boundary
- Default: line
- layer=integer
- Layer number
- A single vector map can be connected to multiple database tables. This number determines which table to use.
- Default: 1
- option=string
- Option
- Options: segment,lines
- Default: segment
- segment: reads segments from standard input
- lines: calculate curvature for all sements of all lines
DESCRIPTION
v.curvature calculates average curvature along a segment
given by from/to distance measured along the line specified by
category.
For individual straight parts of the line, the average curvature as
calculated from directions of adjacent parts. An average of specified
segment is then calculated as average from curvatures of line parts
(lengths of line parts overlapped by specified segment are taken into
acount).
This method may be used only if line data digitized with appropriate
accuracy, where 'appropriate' depend on an application we want to use
it for and on the length of the segment we want to calculate the
curvature for.
If user needs curvature for too small segments compared to the density
of vertices on lines, the lines should be smoothed beforehand with
some other module (this approach is preferred to internal smoothing
(interpolating) within v.curvature, because automatic smoothing may
often result in unexpected, unwanted shapes, and user should see which
data are really processed).
With the 'segment' option, the module reads from 'stdin':
- segment_id line_category from to
- segment_id - identifier for one segment we need curvature for
- line_category - category of line the segment is on:
- from - distance of segment start from the beginnig of the line
- to - distance of end of segment from the beginnig of the line
Note that if segment limits may exceed the line, segment is cut
by line ends.
Output is written to 'stdout' in format:
segment_id average_curvature average_radius
AUTHOR
Radim Blazek, ITC-Irst, Trento, Italy
Last changed: $Date$
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