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

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   v.to.rast will only affect data in areas lying inside the boundaries of
   the current geographic region. 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 [1]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
   [2]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.

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   1. 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 in=vect_map out=raster_map col=SPEED

   2. Calculate stream directions from a river vector map (Spearfish)

v.to.rast in=streams out=streamsdir use=dir

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

v.to.rast in=fields out=myfields use=attr col=cat labelcol=label
r.category myfields

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   [3]db.describe, [4]v.category

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   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: 2008-02-19 14:18:46 -0600 (ÐÑ, 19 Ñев 2008) $

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References

   1. file://localhost/root/tmp/2/fin/db.describe.html
   2. file://localhost/root/tmp/2/fin/v.category.html
   3. file://localhost/root/tmp/2/fin/db.describe.html
   4. file://localhost/root/tmp/2/fin/v.category.html