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v.overlay(1grass) | Grass User's Manual | v.overlay(1grass) |
NAME¶
v.overlay - Overlays two vector maps.KEYWORDS¶
vector, geometrySYNOPSIS¶
v.overlayFlags:¶
- -t
-
- --overwrite
-
- --verbose
-
- --quiet
-
Parameters:¶
- ainput=name
-
- atype=string[,string,...]
-
- alayer=integer
-
- binput=name
-
- btype=string[,string,...]
-
- blayer=integer
-
- output=name
-
- operator=string
-
- olayer=integer[,integer,...]
-
- snap=float
-
DESCRIPTION¶
v.overlay allows the user to overlay two vector maps. Features in ainput can be lines or areas and are cut with areas in binput. Simple clipping can be performed with the and operator. If areas in ainput are overlaid with areas in binput, it is sometimes necessary to snap areas of binput to those of ainput, otherwise areas can go missing or many sliver areas can be created. Snapping is enabled by default and can be disabled by setting the snap option to a negative value. Recommended values are between 0.00000001 and 0.0001. Using larger values for snapping can have undesired side-effects, but may sometimes be necessary to get a clean output (see example below). In general, it is recommended to start with a small snapping threshold, gradually increasing the threshold until the result is reasonably clean. Snapping modifies only boundaries in binput, which are snapped to boundaries in ainput. Boundaries in ainput are not modified. If the first number of the olayer option is > 0, then the resulting output map has a merged attribute table in the given layer number. The original column names have a prefix ( a_ and b_) corresponding to ainput and binput map. If the second number of the olayer option is > 0, then the categories of ainput in layer alayer are transferred to the output layer with the second number. If the third number of the olayer option is > 0, then the categories of binput in layer blayer are transferred to the output layer with the third number.NOTES¶
Currently only areas in ainput are supported for the operators or and xor! See also v.select. The operator defines what kind of operation will be done. Features are written to output, if the result of an operation 'ainput operator binput' is true. If the first number of the olayer option is > 0, then attributes of the tables from ainput and binput are joined into a new table linked to the output map with a new cat column. If the second number of the olayer option is > 0, then the attribute table of ainput is copied to the output map. If the third number of the olayer option is > 0, then the attribute table of binput is copied to the output map.EXAMPLES¶
Polygons overlaid with ploygons¶
Lines overlaid with polygons¶
Using the North Carolina sample dataset, we clip the roads map to the area of city of Raleigh, preserving road attributes in layer 1:where="ZIPNAME = 'RALEIGH'"
out=roadsmajor_raleigh operator=and \
SEE ALSO¶
v.db.connect, v.select, g.copyAUTHORS¶
Radim Blazek, ITC-Irst, Trento, ItalyGRASS 6.4.4 |