MapServer queries, at least some of them, respect layer tolerances which effectively acts like a buffer. You can also take the result of your buffering operation and use it in a queryByShape() operation. Make sure you set your layer tolerances appropriately (probably to 0) so that you get features that intersect with the shape.
Steve From: [email protected] [mailto:[email protected]] On Behalf Of Bistrais, Bob Sent: Tuesday, February 15, 2011 1:54 PM To: Lime, Steve D (DNR) Cc: mapserver-users Subject: RE: [mapserver-users] Buffer features? OK, that makes sense. One more thing I'm not clear on- I can draw my buffer around the selected feature. How can this buffer now be used to query another layer? I guess it's similar to other queries, but how to select this buffer feature and use it as the input to the query? ________________________________ From: Lime, Steve D (DNR) [mailto:[email protected]] Sent: Tuesday, February 15, 2011 1:43 PM To: Bistrais, Bob Cc: mapserver-users Subject: RE: [mapserver-users] Buffer features? You'd need to use 3 different layers and change your code to create 3 different buffered shapes accordingly. Steve From: [email protected] [mailto:[email protected]] On Behalf Of Bistrais, Bob Sent: Tuesday, February 15, 2011 12:30 PM To: Lime, Steve D (DNR) Cc: mapserver-users Subject: RE: [mapserver-users] Buffer features? Not to make life more difficult, but is it possible to create a multi-ring buffer, basically 3 polygons at 3 different distances from a selected feature? ________________________________ From: Lime, Steve D (DNR) [mailto:[email protected]] Sent: Tuesday, February 15, 2011 12:22 PM To: Tamas Szekeres Cc: mapserver-users Subject: RE: [mapserver-users] Buffer features? Not quite, I'm thinking of a single layer setup: LAYER DATA myfile.shp # or whatever connection information is necessary TYPE POLYGON STATUS DEFAULT NAME 'buffered_shapes' GEOMTRANSFORM (buffer([shape], 500)) # buffer each shape by 500 map units # classes and styles follow TEMPLATE 'void' END The GEOMTRANSFORM would be applied as shapes are pulled from a data source so you would draw or, potentially, query the transformed shapes. The difference between a layer-level GEOMTRANSFORM and a style-level one is the coordinates they operate on. Layer-level work would be done on a raw feature in map coordinates and style-level works on pixels. We do layer-level stuff already, conceptually, in the form of projections and clipping. The GEOMTRANSFORM just provides a way of extending that work... Note this type of GEOMTRANSFORM expression is working for buffers in STYLEs in trunk (but using pixels for the moment). Steve From: Tamas Szekeres [mailto:[email protected]] Sent: Tuesday, February 15, 2011 11:12 AM To: Lime, Steve D (DNR) Cc: mapserver-users Subject: Re: [mapserver-users] Buffer features? Steve, Did you mean to achieve something like?: LAYER CONNECTIONTYPE TRANSFORM CONNECTION sourcelayer # reference to another layer NAME transformlayer PROCESSING "TRANSFORM=(buffer([shape]))" TEMPLATE query.html .... END LAYER CONNECTIONTYPE SHAPE DATA myfile.shp NAME sourcelayer .... END Which is simple and easy to implement. Best regards, Tamas 2011/2/15 Lime, Steve D (DNR) <[email protected]<mailto:[email protected]>> I'd approach RFC 22, especially the transform piece, differently now with the parser changes implemented in 6.0. We now have (with GEOS enabled) an expression syntax available to support things like buffering, convex hull, differences, etc... or combinations thereof. I'd implement layer-level GEOMTRANSFORMs in that case using these expressions. On the query result side of things I'd consider adding a layer template as a layer option. This would kinda work like the approach outlined for Bob. You'd define a presentation template layer (no DATA value) and run the query results through it instead of the regular layer (for certain querymap types, e.g. highlight). Steve From: [email protected]<mailto:[email protected]> [mailto:[email protected]<mailto:[email protected]>] On Behalf Of Tamas Szekeres Sent: Tuesday, February 15, 2011 3:06 AM To: Bistrais, Bob Cc: mapserver-users Subject: Re: [mapserver-users] Buffer features? In accordance with the problem mentioned, I recall a resonable enhancement as described in RFC22a<http://www.mapserver.org/development/rfc/ms-rfc-22a.html> which would provide an option to configure all the stuff in the mapfile (not requiring MapScript) and would make it easier to customize the query maps as well. With this enhancement 2 new layer data providers could be implemented, like: 1. CONNECTIONTYPE=QUERYRESULT would provide to represent the result sets of one layer in a new layer. 2. CONNECTIONTYPE=TRANSFORM would provide simple geometry transformations on a source layer and then provide the modified features as a new layer. By chaining these layers together in a map configuration we could get such results<http://trac.osgeo.org/mapserver/attachment/ticket/2128/sample4.png> as included in the RFC document. I consider this kind of enhancement could be implemented within the scope of 1-2 days of work (comparable with a fully elaborated MapScript solution providing the same) Best regards, Tamas 2011/2/14 Bistrais, Bob <[email protected]<mailto:[email protected]>> This question may have come up before, but I haven't found it in the archives. I would like to take a selected feature and buffer it to a specified distance. I know it's possible to do a queryByPoint with a buffer distance, but I need to create an actual buffer shape to display on the map. Has anyone done something like this before? Does MapServer have this capability? _______________________________________________ mapserver-users mailing list [email protected]<mailto:[email protected]> http://lists.osgeo.org/mailman/listinfo/mapserver-users
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