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
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
v.category input=testmap output=outmap option=del cat=-1
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
v.category input=wkt output=wktnew option=add
v.category input=observer output=observer_new option=transfer layer=1,2,3,4,5,6,7,8
v.category input=roads option=print layer=1 id=1-50
Available at: v.category source code (history)
Latest change: Thursday Feb 03 11:10:06 2022 in commit: 547ff44e6aecfb4c9cbf6a4717fc14e521bec0be
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