Hello,
I am trying to understand how vector reprojection works. I am working in C++ and I saw that I could set the coordinate system on the map object and on the layer object as well. So I guess that is the layer' srs is different from the map one's, there should be a reprojection. But . a blank image is so far the only result I have . I have shapefiles in ESRI 54004 World Mercator with the srs: "+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs" If I set this srs on both object, map and layer, I have my map displayed. If I set it on only one object (then the other should be default WGS 1984) it leads to a blank image. I tried to set manually the srs WGS 1984 : "+proj=longlat +ellps=WGS84 +datum=WGS84 +units=m +no_defs" but with the same observation, I have to set the same srs on both object to have my map displayed. So I was wondering if I am doing right because if layer' srs can't be different from map's . where is the point to set it ? So let's say that I have shape files in a projection A and I want a map on a projection B how should I handle it ? Right now I just set it on the map and make a "layer.set_srs(map.get_srs());" but I am not sure that it will work in any situations. Thank you for lighting up my lantern. Regards, Nicolas
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