DESCRIPTION

v.to.rast transforms GRASS vector map layers into GRASS raster map layer format. Optionally, attributes can be converted into raster category labels.

NOTES

v.to.rast will only affect data in areas lying inside the boundaries of the current geographic region. A grid cell belongs to the area where the grid cell center falls into.

Before running v.to.rast, the user should therefore ensure that the current geographic region is correctly set and that the region resolution is at the desired level.

Either the column parameter or the value parameter must be specified. The use option may be specified alone when using the dir option.

use options are:

attr - read values from attribute table (default)
cat - read values from category
val - use value specified by value option
z - use z coordinate (points or contours only)
dir - output as flow direction in degrees (lines only)

The column parameter uses an existing column from the vector map database table as the category value in the output raster map. Existing table columns can be shown by using db.describe.

An empty raster map layer will be created if the vector map layer has not been assigned category/attribute labels (e.g., through use of v.category option=add).

Otherwise:

Labeled areas and/or centroids will produce filled raster coverages with edges that straddle the original area boundary as long as the boundary is NOT labeled.
(Use v.category option=del type=boundary to remove.)
Labeled lines and boundaries will produce lines of raster cells which touch the original vector line. This tends to be more aggressive than area-only conversions.
Points and orphaned centroids will be converted into single cells on the resultant raster map.

Flow directions are given in degrees counterclockwise from east.

Raster category labels are supported for all of use= except use=z.

The -d flag applies only to lines, the default is only those on the render path (thin line).

EXAMPLES

Convert a vector map and use column SPEED from attribute table

db.describe -c table=vect_map

ncols:3
Column 1: CAT
Column 2: SPEED
Column 3: WIDTH

v.to.rast input=vect_map output=raster_map attribute_column=SPEED

Calculate stream directions from a river vector map (Spearfish)

v.to.rast input=streams output=streamsdir use=dir

Convert a vector polygon map to raster including descriptive labels (Spearfish)

v.to.rast input=fields output=myfields use=attr attribute_column=cat label_column=label
r.category myfields

AUTHORS

Original code: Michael Shapiro, U.S. Army Construction Engineering Research Laboratory
GRASS 6.0 updates: Radim Blazek, ITC-irst, Trento, Italy
Stream directions: Jaro Hofierka and Helena Mitasova
GRASS 6.3 code cleanup and label support: Brad Douglas

Last changed: $Date$