v.to.rastgrass - Online in the Cloud

PROGRAM:

NAME

v.to.rast - Converts (rasterize) a vector map into a raster map.

KEYWORDS

vector, conversion, raster, rasterization

SYNOPSIS

v.to.rast
v.to.rast --help
v.to.rast [-d] input=name [layer=string] [type=string[,string,...]] [cats=range]
[where=sql_query] output=name use=string [attribute_column=name] [rgb_column=name]
[label_column=name] [value=float] [memory=integer] [--overwrite] [--help]
[--verbose] [--quiet] [--ui]

Flags:
-d
Create densified lines (default: thin lines)
All cells touched by the line will be set, not only those on the render path

--overwrite
Allow output files to overwrite existing files

--help
Print usage summary

--verbose
Verbose module output

--quiet
Quiet module output

--ui
Force launching GUI dialog

Parameters:
input=name [required]
Name of input vector map
Or data source for direct OGR access

layer=string
Layer number or name
Vector features can have category values in different layers. This number determines
which layer to use. When used with direct OGR access this is the layer name.
Default: 1

type=string[,string,...]
Input feature type
Options: point, line, area
Default: point,line,area

cats=range
Category values
Example: 1,3,7-9,13

where=sql_query
WHERE conditions of SQL statement without ’where’ keyword
Example: income < 1000 and inhab >= 10000

output=name [required]
Name for output raster map

use=string [required]
Source of raster values
Options: attr, cat, val, z, dir
attr: read values from attribute table
cat: use category values
val: use value specified by value option
z: use z coordinate (points or contours only)
dir: output as flow direction (lines only)

attribute_column=name
Name of column for ’attr’ parameter (data type must be numeric)

rgb_column=name
Name of color definition column (with RRR:GGG:BBB entries)

label_column=name
Name of column used as raster category labels

value=float
Raster value (for use=val)
Default: 1

memory=integer
Maximum memory to be used (in MB)
Cache size for raster rows
Default: 300

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

Convert vector points to raster with raster cell binning
In this example, the number of schools per raster cell are counted (North Carolina sample
dataset):
g.copy vector=schools_wake,myschools_wake
# set computation region for raster binning
g.region vector=myschools_wake res=5000 -p -a
# add new column for counting
v.db.addcolumn myschools_wake column="value integer"
v.db.update myschools_wake column=value value=1
# verify attributes
v.db.select myschools_wake column=cat,value
v.out.ascii input=myschools_wake output=- column=value
# export and import on the fly, use 4th column (value) as input
v.out.ascii input=myschools_wake output=- column=value | r.in.xyz input=- \
z=4 output=schools_wake_aggreg method=sum
d.mon wx0
d.rast schools_wake_aggreg
d.vect schools_wake
d.grid 5000
Number of schools per raster cell

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