.TH v.to.points 1grass "" "GRASS 6.4.2" "Grass User's Manual"
.SH NAME
\fI\fBv.to.points\fR\fR  - Create points along input lines in new vector with 2 layers.
.SH KEYWORDS
vector, geometry
.SH SYNOPSIS
\fBv.to.points\fR
.br
\fBv.to.points help\fR
.br
\fBv.to.points\fR [-\fBnvit\fR] \fBinput\fR=\fIname\fR \fBoutput\fR=\fIname\fR  [\fBtype\fR=\fIstring\fR[,\fIstring\fR,...]]   [\fBllayer\fR=\fIinteger\fR]   [\fBdmax\fR=\fIfloat\fR]   [--\fBoverwrite\fR]  [--\fBverbose\fR]  [--\fBquiet\fR] 
.SS Flags:
.IP "\fB-n\fR" 4m
.br
Write line nodes
.IP "\fB-v\fR" 4m
.br
Write line vertices
.IP "\fB-i\fR" 4m
.br
Interpolate points between line vertices
.IP "\fB-t\fR" 4m
.br
Do not create attribute table
.IP "\fB--overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB--verbose\fR" 4m
.br
Verbose module output
.IP "\fB--quiet\fR" 4m
.br
Quiet module output
.PP
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR" 4m
.br
Input vector map containing lines
.IP "\fBoutput\fR=\fIname\fR" 4m
.br
Output vector map where points will be written
.IP "\fBtype\fR=\fIstring[,\fIstring\fR,...]\fR" 4m
.br
Feature type
.br
Options: \fIpoint,line,boundary,centroid,area\fR
.br
Default: \fIpoint,line,boundary,centroid\fR
.IP "\fBllayer\fR=\fIinteger\fR" 4m
.br
Layer number
.br
Line layer
.br
Default: \fI1\fR
.IP "\fBdmax\fR=\fIfloat\fR" 4m
.br
Maximum distance between points in map units
.br
Default: \fI100\fR
.PP
.SH DESCRIPTION
\fIv.to.points\fR creates points along input lines. The output is a vector with 2 layers.
Layer 1 holds the category and attributes of the input lines; all points created along the
same line have the same category, equal to the category of that line. In layer 2 each point
has it's unique category; other attributes stored in layer 2 are \fIlcat\fR - the
category of the input line and \fIalong\fR - the distance from line's start.
.SH NOTES
The \fIdmax\fR parameter is the maximum limit but not an exact
distance. To place points with exact distance from the beginning
of the vector line the user should use
v.segment.
.PP
The \fItype\fR parameter is used to control which input vector
geometry types to convert into points. 
Some caveats to consider about this parameter:
.RS
.IP
Points and centroids can be considered as "lines" with only one
node. Consequently, the result of selecting \fIpoint\fR or
\fIcentroid\fR as the type parameter is that all points/centroids
get written into the output vector. The original category numbers of
the input points/centroids get written to the '\fI\fIlcat\fR\fR'
attribute in layer 2 of the output vector. All values for
\fIalong\fR are zero in the output vector, as only point geometry
was used for input (there is no linear distance to calculate
\fIalong\fR, as each point/centroid is the start \fI\fIand\fR\fR
end of its own "line".
.IP
Boundaries are treated as lines, with points getting interpolated
along the boundary perimeter according to \fIdmax\fR. If two
adjoining polygons share a topological boundary, the boundary only
gets converted to points once.
.IP
If the \fItype\fR parameter is set to \fIarea\fR, the boundary of
each area is converted to points \fIregardless\fR of whether or not
there is a topological boundary between adjacent areas. In other
words, the common boundary of two adjoining areas, for example, gets
converted to points twice. The centroid is not converted to a point in
the output vector for \fItype=area\fR.
.RE
The -v flag is used to digitize points that fall on the line's vertices \fIonly\fR.
\fIdmax\fR is ignored in this case. 
.PP
If the -i flag is used in conjunction with the -v flag,
\fIv.to.points\fR will digitize points on the line vertices, as
well as interpolate points between line vertices using \fIdmax\fR
as the maximum allowable spacing.
.PP
To get points created for the beginning, middle and end only, use
the -i switch and set \fIdmax\fR so that:
.PP
(length of input line / 2) <= \fIdmax\fR <= length of input line
.PP
So if \fIdmax\fR is between 0.5x and 1.0x the line length, you
will always get points created at exactly the beginning, middle and
end of the input line.
.SH EXAMPLE
In this example, the 't_powerlines' vector lines map in the
Spearfish 6
location is used to create points along the input lines:
\fC
.DS
.br
v.to.points in=t_powerlines out=t_powerlines_points dmax=120
.br
d.vect t_powerlines_points
.br
.DE
\fR
.SH SEE ALSO
\fI
v.segment,
v.to.rast,
v.to.db
\fR
.SH AUTHOR
Radim Blazek
.PP
\fILast changed: $Date: 2011-11-08 12:29:50 +0100 (Tue, 08 Nov 2011) $\fR
.PP
Full index
.PP
© 2003-2011 GRASS Development Team