DESCRIPTION
v.to.points creates points along input 2D or 3D lines,
boundaries and faces. Point features including centroids and kernels
are copied from input vector map to the output. For details see notes
about type parameter.
The output is a vector map with 2 layers. Layer 1 holds the category
of the input features; 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 lcat - the category of the input line and along
- the distance from line's start.
By default only features with category are processed,
see llayer parameter for details.
NOTES
The dmax 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.
Set llayer to -1 to process features from all layers including
features without category. Features will be assigned new unique
categories at layer 1. Option llayer=-1 should be used to
convert boundaries, as in most of cases boundaries lack category
values.
The type parameter is used to control which input vector
geometry types to convert into points. Some caveats to consider about
this parameter:
-
Points and centroids can be considered as "lines" with only one
node. Consequently, the result of selecting point or
centroid as the type parameter is that all
points/centroids get written into the output vector map. The
original category numbers of the input points/centroids get
written to the 'lcat' attribute in layer 2 of the output
vector map. All values for along are zero in the output
vector map, as only point geometry was used for input (there is no
linear distance to calculate
along, as each point/centroid is the start and
end of its own "line").
-
Boundaries are treated as lines, with points getting interpolated
along the boundary perimeter according to dmax. If two
adjoining polygons share a topological boundary, the boundary only
gets converted to points once.
-
If the type parameter is set to area, the boundary of
each area is converted to points regardless 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 type=area.
The use=vertex option is used to digitize points that fall on
the line's vertices only. Parameter dmax is ignored in
this case. Similarly to use=node when only line's node are
used.
If the -i flag is used in conjunction with
the use=vertex option,
v.to.points will digitize points on the line vertices, as
well as interpolate points between line vertices using dmax as
the maximum allowable spacing.
To get points created for the beginning, middle and end only, use
the -i flag and set dmax so that:
(length of input line / 2) <= dmax <= length of input line
EXAMPLE
In this example, the 't_powerlines' vector lines map in the
Spearfish 6
location is used to create points along the input lines:
v.to.points in=t_powerlines out=t_powerlines_points dmax=120
SEE ALSO
v.segment,
v.split,
v.to.rast,
v.to.db
AUTHOR
Radim Blazek
Updated to GRASS 7 by Martin Landa, Czech Technical University in
Prague, Czech Republic
Last changed: $Date$