Provided by: grass-doc_8.3.0-1_all 
NAME
v.category - Attaches, deletes or reports vector categories to/from/of map geometry.
KEYWORDS
vector, category, layer
SYNOPSIS
v.category
v.category --help
v.category [-gt] input=name [layer=string[,string,...]] [type=string[,string,...]]
[ids=range] [output=name] option=string [cat=integer] [step=integer] [--overwrite]
[--help] [--verbose] [--quiet] [--ui]
Flags:
-g
Shell script style, currently only for report
Format: layer type count min max
-t
Do not copy attribute table(s)
--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[,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, boundary, centroid, area, face, kernel
Default: point,line,centroid,face
ids=range
Feature ids (by default all features are processed)
Example: 1,3,7-9,13
output=name
Name for output vector map
option=string [required]
Action to be done
Options: add, del, chlayer, sum, report, print, layers, transfer
add: add a category to features without category in the given layer
del: delete category (cat=-1 to delete all categories of given layer)
chlayer: change layer number (e.g. layer=3,1 changes layer 3 to layer 1)
sum: add the value specified by cat option to the current category value
report: print report (statistics), in shell style: layer type count min max
print: print category values, layers are separated by ’|’, more cats in the same layer
are separated by ’/’
layers: print only layer numbers
transfer: copy values from one layer to another (e.g. layer=1,2,3 copies values from
layer 1 to layer 2 and 3)
cat=integer
Category value
Default: 1
step=integer
Category increment
Default: 1
DESCRIPTION
v.category attaches, copies, deletes or reports categories to/from/of vector geometry
objects. Further on, v.category adds a number given by the cat option to categories of the
selected layer. These categories (IDs) are used to assign IDs or to group geometry
objects into categories (several different geometry objects share the same category).
These categories are also used to link geometry object(s) to attribute records (from an
attribute table linked to vector map).
NOTES
Use v.to.db to upload related categories to a linked attribute table.
The type parameter specifies the type of geometry objects to which the category is added;
it is similar to an input filter - only the geometry specified in ’type’ is processed.
If the type parameter is set to centroid and the option parameter set to add, new
categories will be added to existing centroids. Note however, that new centroids cannot be
created this way. To do so, they must be added manually using wxGUI vector digitizer or
by running v.category with the type parameter set to area.
If categories are copied with option=transfer, a warning is issued if categories already
exit in the layer they are copied to. In this case the user must make sure beforehand that
copying categories from one layer to another layer does not cause undesired grouping of
different geometry objects into the same categories. This can be avoided by specifying
only one layer. The module will then find the next free layer number and copy categories
to there. The new layer number is reported at the end.
Areas are a special case because it is impossible to attach a cat to an area without a
centroid; in this case, the module places new centroids in areas automatically for
type=area.
The cat parameter is only used with option=add, option=sum and option=del.
Categories can be deleted for the given layer with option=del. If cat is set to -1, all
categories for the given layer are deleted. If cat is zero or positive, only this category
value will be deleted. By default, cat is set to 1 which means that only categories of
value 1 will be deleted.
With option=report, the module reports for each layer and type the total number of
categories, the minimum and the maximum category number. If there are e.g. two lines with
line 1 having category 1 and line 1 having categories 1 and 2, then there are a total of
three category values with minimum 1 and maximum 2.
The ids parameter specifies the list of feature IDs to which the operation is performed;
by default, all vector feature ids are processed. The feature ID is an internal (unique)
geometry ID that all vector primitives possess, and is separate from any category the
feature may also possess. Use
v.edit map=inputname tool=select
to find out the geometry ids of certain features.
EXAMPLES
Report vector categories
v.category input=testmap option=report
LAYER/TABLE 1/testmap:
type count min max
point 0 0 0
line 1379 1 1379
boundary 0 0 0
centroid 0 0 0
area 0 0 0
all 1379 1 1379
Delete all vector categories in layer 1
v.category input=testmap output=outmap option=del cat=-1
Add vector categories in layer 1 with step=2
v.category input=outmap output=stepmap option=add step=2
# report
v.category input=stepmap option=report
LAYER/TABLE 1/outmap:
type count min max
point 0 0 0
line 1379 1 2757
boundary 0 0 0
centroid 0 0 0
area 0 0 0
all 1379 1 2757
Add categories/centroids to a vector map without categories
v.category input=wkt output=wktnew option=add
Results can be tested using d.what.vect.
Copy categories from layer 1 to layer 2,3,4,5,6,7 and 8
Existing layer will be overwritten, non-existing will be created.
v.category input=observer output=observer_new option=transfer layer=1,2,3,4,5,6,7,8
Print vector categories of given layer
Print vector categories from the first layer, only for feature ids 1-50.
v.category input=roads option=print layer=1 id=1-50
SEE ALSO
v.centroids, v.db.connect, v.edit, v.to.db
AUTHOR
Radim Blazek, ITC-irst, Trento, Italy
Modified (the id parameter) by Martin Landa, FBK-irst (formerly ITC-irst), Trento, Italy,
2008/02
SOURCE CODE
Available at: v.category source code (history)
Accessed: Tuesday Jun 27 11:13:42 2023
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