On 15/12/15 10:12, Paulo van Breugel wrote:
On Tue, Dec 15, 2015 at 9:15 AM, Moritz Lennert <[email protected] <mailto:[email protected]>> wrote: On 15/12/15 00:22, Martin Landa wrote: Hi, 2015-12-15 0:18 GMT+01:00 Alec Ventura <[email protected] <mailto:[email protected]>>: I run the v.buffer with the -t flag and everything is ok now I wonder if attributes should be copied by default (without need to set up any flag). v.buffer fusions the geometries of buffers by default. Keeping the attribute table does not make sens in that case as one buffer geometry can be the result of many different input geometries. This also means that you cannot retrieve the buffer of a specific input geometry. When you use the -t flag, buffers are cut up into separate parts and each one that is the result of several overlapping buffers has multiple categories. As the man page says: "The resulting buffer areas can have multiple categories, and multiple buffer areas can have the same category. The buffer for the input feature with category X can thus be retrieved by selecting all buffer areas with category X". The above is actually a nice and more explicit explanation of what v.buffer does, especially for (new) users that get confused by the consequences of GRASS' topological vector format and handling. Why not add this to the manual page, perhaps something along the line of: "v.buffer fusions the geometries of buffers by default. Categories and attribute table will not be transferred (this would not make sense as one buffer geometry can be the result of many different input geometries). To transfer the categories and attributes can be done with the *t* flag. This will result in buffers being cut up where buffers of individual input geometries overlap. Each part that is the result of overlapping buffers of multiple geometries will have multiple categories corresponding to those geometries. Multiple buffer areas can also have the same category. The buffer for the input feature with category X can thus be retrieved by selecting all buffer areas with category X (see example below). " (this would replace: "Categories and attributes can be transferred with the *t* flag. The resulting buffer areas can have multiple categories, and multiple buffer areas can have the same category. The buffer for the input feature with category X can thus be retrieved by selecting all buffer areas with category X (see example below).")
Done in trunk: r67143. If the result suits you, we can backport to grass70. Moritz _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
