[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
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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 =/
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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
>
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>
> (\__/)
> (='.'=)This is Bunny. Copy and paste bunny
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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
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are no such people" --Oscar Wilde
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