Le lundi 08 février 2016 15:54:11, Daniel Fenton a écrit : > Hi Maning, > > For NAD83 you need to convert the Datum to WGS84. The WKT string you show > does not include that conversion. Proj.4 is missing these in a lot of > cases. > > Try this string instead: > > PROJCS["NAD83_California_zone_5_ftUS",GEOGCS["GCS_North_American_1983",DATU > M["D_North_American_1983",SPHEROID["GRS_1980",6378137,298.257222101]],TOWGS > 84[-0.9956,1.9013,0.5215,0.025915,0.009426,0.011599,-0.00062],PRIMEM["Green > wich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Lambert_Conformal > _Conic"],PARAMETER["standard_parallel_1",35.46666666666667],PARAMETER["stan > dard_parallel_2",34.03333333333333],PARAMETER["latitude_of_origin",33.5],PA > RAMETER["central_meridian",-118],PARAMETER["false_easting",6561666.667],PAR > AMETER["false_northing",1640416.667],UNIT["Foot_US",0.30480060960121924]] > > Hopefully that works for you. Let me know if it doesn't.
(CC'ing proj mailing list) That's interesting, as indeed, proj assumes that WGS84 == NAD83, if no extra parameters are specified. Comparing the TOWGS84 values you suggest with the EPSG database, I see you suggest using EPSG:6866 coordinate transformation "ITRF2000 to NAD83(CORS96)" (actually the opposite transformation, NAD83(CORS96) to ITRF2000). Wondering if it might be appropriate to change proj.4 defaults to the above ? Although it is not clear to me which realization of WGS84 is supposed to be the one used by proj.4 as its pivot when datum transformations are involved. I guess this must depends on the semantics of the grid or towgs84 parameters used... There's also the EPSG:6864 (ITRF96 to NAD83(CORS96)) values that could be used if we rely rather on the original WGS84 realization : -0.9910, 1.9072,0.5129,0.02579,0.00965,0.01166,0 Using the HTDP grids ( https://trac.osgeo.org/proj/wiki/HTDPGrids ) might also be an option. Indeed Daniel's suggestion seems to do the trick, or at least better match other data from the site http://geohub.lacity.org/datasets/813fcefde1f64b209103107b26a8909f_0 . I see it has also a geojson output : http://geohub.lacity.org/datasets/813fcefde1f64b209103107b26a8909f_0.geojson And the first feature returned is OBJECT_ID=4001 whose first vertex is : -118.276946349107,33.7920287419671 If I do, ogr2ogr -f kml /vsistdout/ /vsizip/Building_Footprints.zip -where "OBJECTID=4001" I get : -118.276934177326,33.7920239166625 which is off by a bit more than 1 meter from the position of the geojson output. But If I do : ogr2ogr -f kml /vsistdout/ /vsizip/Building_Footprints.zip -where "OBJECTID=4001" \ -s_srs "+proj=lcc +lat_1=35.46666666666667 +lat_2=34.03333333333333 \ +lat_0=33.5 +lon_0=-118 +x_0=2000000.000101601 +y_0=500000.0001016002 \ +ellps=GRS80 +towgs84=-0.9956,1.9013,0.5215,0.025915,0.009426,0.011599,-0.00062 +units=us-ft +no_defs" \ -t_srs EPSG:4326 I get: -118.276946349109,33.7920287419681 which is identical to the geojson output (difference is in the 10 micrometer precision range) > > Daniel Fenton > Software Engineer > Esri R&D > > On Mon, Feb 8, 2016 at 6:56 AM maning sambale <[email protected]> > > wrote: > > Hi, > > > > I'm trying to convert LA City building data from State Plane to > > EPSG:4326. I converted the data using ogr2ogr. Visually inspecting > > using Bing imagery, I'm seeing an offset. > > > > Details of SRS info and sample images here: > > https://gist.github.com/maning/093a866fd465ea880032 > > > > It is possible that Bing has the offset, but the source of Bing comes > > from LARIAC (Los Angeles Region Imagery Acquisition Consortium) > > imagery, the same source as the building footprints were traced. > > > > Any hints on the "proper" conversion from State Plane to EPSG:4326. > > > > -- > > cheers, > > maning > > ------------------------------------------------------ > > "Freedom is still the most radical idea of all" -N.Branden > > https://epsg4253.wordpress.com/ > > http://twitter.com/maningsambale > > ------------------------------------------------------ > > _______________________________________________ > > gdal-dev mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/gdal-dev -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
