Hi Marco On Fri, Jan 7, 2011 at 9:20 PM, Marco Hugentobler <marco.hugentob...@sourcepole.ch> wrote: > Hi Martin > >> On-th-fly raster reprojection is not (IMHO) very expensive. The >> complexity depends on the desired output quality (e.g. what type of >> interpolation is used) and raster size. I would expect that most of >> the raster rendering time is fetching of source data, the warping >> itself is simple. > > Afaik raster reprojection is very expensive (see e.g. > http://mapserver.org/input/raster.html#raster-warping). And the 2-4 times is > only with umn mapservers clever linearisation along scanlines. With a normal > warp, it will be much more.
Even though reprojection is expensive, it's probably better to reproject the layer than to render it misaligned :-) Anyway reprojecting every single point using the coordinate transform formulas wastes a lot of processing power and should be done more wisely. We have this problem also with reprojecting of vector layers (every single points is reprojected using the expensive formula). >> > THird: Having OTF automatic still won't help users with data that lacks a >> > CRS. >> >> No, but at least they can get a notification that a layer has unknown >> CRS and thus can be aligned incorrectly. > > I'm concerned that such a warning could scare newbie users who don't know > about spatial reference systems at all (and it will be one of the first things > they see if the datasource crs is not recognized. This happens frequently if > the data comes from a commercial GIS). > > A very important use case here is people working with governemental data > provided by the local GIS department. The GIS dep. provides everything in the > same meter CRS and the normal user does not need to know about it, since > everything overlays properly. Ideally if all the data from government is in the same CRS, no reprojecting will happen - because the project CRS will be the same as the CRS of individual layers (thus no warning would be issued). Martin _______________________________________________ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer