Re: [Geotools-gt2-users] lookup features within a radius?

[Yang <ted...@gm...>]

actually I just looked at the  ogrinfo -al   output of the shape file,
it seems that because when I generated the file, I called


        SimpleFeatureTypeBuilder builder = new SimpleFeatureTypeBuilder();
        builder.setCRS(DefaultGeographicCRS.WGS84); // <- Coordinate
reference system

the shape file is marked as in the WGS84 coordinate system:

ogrinfo -al /tmp/ttt.shp
INFO: Open of `/tmp/ttt.shp'
      using driver `ESRI Shapefile' successful.

Layer name: ttt
Geometry: Point
Feature Count: 2
Extent: (0.000000, 0.000000) - (100.000000, 0.000000)
Layer SRS WKT:
GEOGCS["WGS84(DD)",
    DATUM["WGS84",
        SPHEROID["WGS84",6378137.0,298.257223563]],
    PRIMEM["Greenwich",0.0],
    UNIT["degree",0.017453292519943295],
    AXIS["Geodetic longitude",EAST],
    AXIS["Geodetic latitude",NORTH]]
gml_id: String (254.0)
OGRFeature(ttt):0
  gml_id (String) = 12345
  POINT (0 0)

OGRFeature(ttt):1
  gml_id (String) = 2222
  POINT (100 0)





so the WGS84 is marking is simply ignored when dwithin() is run, and it
simply assumes a flat coordinate system?

Thanks
Yang

On Sat, Jan 28, 2012 at 3:56 AM, Andrea Aime
<and...@ge...>wrote:

> On Fri, Jan 27, 2012 at 11:57 PM, Yang <ted...@gm...> wrote:
>
>> currently we use FilterFactory2.dwithin(geo1, point, distance, units) to
>> lookup the features within a radius of "distance" from "point"
>>
>> but the features in the collection are represented using lat-long,
>> so if FilterFactory2 treats them just as a flat 2-D coordinate system,
>> the distance computed at higher latitude is going to be higher than
>> real distance. so the above lookup actually looks up not a circle, but an
>> ellipse.
>>
>>
>> it seems that to do a real circle lookup, we need dwithin to accept a
>> function as parameter, instead of distance. right? but given the current
>> geotools code, is there a way to achieve circle lookup?
>>
>
> Interface wise, it would just have to respect the unit of measure and
> internally do the proper distance calculations.
> However doing a proper calculation internally is definitely not easy, and
> the point is not the only geometry we
> care about, dwithin must work for any type of reference geometry.
>
> There are some ideas on how to handle the issue here:
> http://jira.codehaus.org/browse/GEOT-1170
> http://jira.codehaus.org/browse/GEOS-937
>
> The solution is not immediate to implement, so far no funding or
> contribution
> showed up to address the problem
>
> Cheers
> Andrea
>
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