[geos-devel] distance
I'm looking at the geos API and I don't undestand what units are the distance parameters supposed to be.. I'm trying to use buffer, to create a 1km circle around a Point defined in SRID=22186, and.. I have no clue how to do this. Thanks Tomas -- "The whole of Japan is pure invention. There is no such country, there are no such people" --Oscar Wilde |_|0|_| |_|_|0| |0|0|0| (\__/) (='.'=)This is Bunny. Copy and paste bunny (")_(") to help him gain world domination. ___ geos-devel mailing list geos-devel@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/geos-devel
Re: [geos-devel] distance
On Fri, Aug 26, 2011 at 9:50 AM, Tomas Neme wrote: > I'm looking at the geos API and I don't undestand what units are the > distance parameters supposed to be.. > > I'm trying to use buffer, to create a 1km circle around a Point > defined in SRID=22186, and.. I have no clue how to do this. > > Thanks > > Tomas Hi Tomas, All the GEOS operations are done in a unitless Cartesian space. Distance is unitless. For example, the distance between a point at (0, 0) and (1, 1) is sqrt(2). 22186 has units of meters, right? As long as your distances are in meters (1000 in your case), you'll be fine. Regards, -- Sean ___ geos-devel mailing list geos-devel@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/geos-devel
Re: [geos-devel] distance
> Hi Tomas, > > All the GEOS operations are done in a unitless Cartesian space. > Distance is unitless. For example, the distance between a point at (0, > 0) and (1, 1) is sqrt(2). 22186 has units of meters, right? As long as > your distances are in meters (1000 in your case), you'll be fine. I thought so, but.. how do I know this? http://www.spatialreference.org/ref/epsg/22186/ this is all the info I could get on 22186, it doesn't say anything about units. we use meters in AR, so I guess you must be right, but not the point.. finding info on this subject is very hard =/ -- "The whole of Japan is pure invention. There is no such country, there are no such people" --Oscar Wilde |_|0|_| |_|_|0| |0|0|0| (\__/) (='.'=)This is Bunny. Copy and paste bunny (")_(") to help him gain world domination. ___ geos-devel mailing list geos-devel@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/geos-devel
Re: [geos-devel] distance
Tomas, If you dig into one of the representations, such as "well known text as HTML" you can see the units. In the WKT it is: PROJCS["POSGAR 94 / Argentina 6", GEOGCS["POSGAR 94", DATUM["Posiciones_Geodesicas_Argentinas_1994", SPHEROID["WGS 84",6378137,298.257223563, AUTHORITY["EPSG","7030"]], TOWGS84[0,0,0,0,0,0,0], AUTHORITY["EPSG","6694"]], PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901"]], UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122"]], AUTHORITY["EPSG","4694"]], UNIT["metre",1, * UNITS * AUTHORITY["EPSG","9001"]], PROJECTION["Transverse_Mercator"], PARAMETER["latitude_of_origin",-90], PARAMETER["central_meridian",-57], PARAMETER["scale_factor",1], PARAMETER["false_easting",650], PARAMETER["false_northing",0], AUTHORITY["EPSG","22186"], AXIS["Y",EAST], AXIS["X",NORTH]] On Fri, Aug 26, 2011 at 11:42 AM, Tomas Neme wrote: >> Hi Tomas, >> >> All the GEOS operations are done in a unitless Cartesian space. >> Distance is unitless. For example, the distance between a point at (0, >> 0) and (1, 1) is sqrt(2). 22186 has units of meters, right? As long as >> your distances are in meters (1000 in your case), you'll be fine. > > I thought so, but.. how do I know this? > > http://www.spatialreference.org/ref/epsg/22186/ > > this is all the info I could get on 22186, it doesn't say anything > about units. we use meters in AR, so I guess you must be right, but > not the point.. finding info on this subject is very hard =/ > > > -- > "The whole of Japan is pure invention. There is no such country, there > are no such people" --Oscar Wilde > > |_|0|_| > |_|_|0| > |0|0|0| > > (\__/) > (='.'=)This is Bunny. Copy and paste bunny > (")_(") to help him gain world domination. > ___ > geos-devel mailing list > geos-devel@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/geos-devel > -- ---+-- I set the clouds in motion - turn up | Frank Warmerdam, warmer...@pobox.com light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Software Developer ___ geos-devel mailing list geos-devel@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/geos-devel
Re: [geos-devel] distance
> If you dig into one of the representations, such as "well known text as HTML" > you can see the units. In the WKT it is: > ... > UNIT["metre",1, * UNITS * =D thanks -- "The whole of Japan is pure invention. There is no such country, there are no such people" --Oscar Wilde |_|0|_| |_|_|0| |0|0|0| (\__/) (='.'=)This is Bunny. Copy and paste bunny (")_(") to help him gain world domination. ___ geos-devel mailing list geos-devel@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/geos-devel