2009/12/7 David Fawcett <[email protected]> > Is GDAL used in the reprojection of WMS images? >
No. GDAL is only used to import shapefiles (and potentially many other format, but it is not implemented). A PROJ4 compatible, boost based libray (boost.geometry, aka GGL), is used for projections. > > This new 1.4 binary is the first instance of Merkaartor that I have > used. When I pulled in a WMS in a UTM SRS (26915), the downloaded > features aligned pretty closely with the WMS image, but there was a > little shift. > > It was close enough that I assumed that the reprojection from 26915 to > geographic or world mercator was happening. > > Of course, maybe you keep the imagery in it's native SRS and then just > use OGR or something to project the vector features. I guess that > would be much less processor intensive. > > Indeed, WMS images are reprojected in the current projection as set in View-Set Projection. "Reprojected" is a big word, as Merkaartor is only deforming the WMS image to fit the current viewport, so misalignement is clearly possible. Best is to use the same projection for the OSM objects and the WMS you are using. You can add custom projections in the ~/.merkaartor/Projections.xml file. The format is the PROJ4 one. - Chris -
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