One more related question. It seems using the VRT format is the way to go. Of course I can make a wrapper around the executable and create a VRT like that. I can also add the functionality to the MapWindow ActiveX control, it is already using GDAL for lots of other stuff. Is gdalbuildvrt.exe easily included in another application or should I stick with the executable?
Does anybody know how QGis is doing it? Thanks, Paul 2012/7/12 Duarte Carreira <[email protected]> > For some reason stats in the individual files did not solve the issue, had > to put it in the vrt. > > Duarte > > -----Mensagem original----- > De: Etienne Tourigny [mailto:[email protected]] > Enviada: quinta-feira, 12 de Julho de 2012 13:28 > Para: Duarte Carreira > Cc: [email protected]; [email protected] > Assunto: Re: [gdal-dev] Tiling aerial photos > > You should generate the stats for every file, as you will probably get > incorrect results with your method > > for f in *.tif; do gdalinfo -stats $f ; done > > On Thu, Jul 12, 2012 at 9:03 AM, Duarte Carreira <[email protected]> > wrote: > > Hi Paul. > > > > > > > > I had to build a big vrt. The one trick that got it loading very fast > > into qgis was adding statistics to each rasterband: > > > > <Metadata> > > > > <MDI key="STATISTICS_MAXIMUM">255</MDI> > > > > <MDI key="STATISTICS_MEAN">111.6784426525</MDI> > > > > <MDI key="STATISTICS_MINIMUM">0</MDI> > > > > <MDI key="STATISTICS_STDDEV">52.100074055799</MDI> > > > > </Metadata> > > > > > > > > I just got stats from a subset and used that for all bands. > > > > > > > > Duarte > > > > > > > > De: Paul Meems (Top-X) [mailto:[email protected]] > > Enviada: quinta-feira, 12 de Julho de 2012 12:11 > > Para: [email protected] > > Assunto: Re: [gdal-dev] Tiling aerial photos > > > > > > > > Thanks Dmitry and Even, > > > > The aerial photos are north-up and are in the same projection and I > > think also in the same resolution. > > It are commercial aerial photos. > > > > The Correlator project sounds very interesting but not necessary in my > case. > > I'll try to implement the VRT format and see what the performance will > be. > > If it is fast we don't need to tile. > > > > Thanks, > > > > Paul > > > > 2012/7/12 Even Rouault <[email protected]> > > > > Selon "Paul Meems (Top-X)" <[email protected]>: > > > >> Thanks Even, > >> > >> http://www.gdal.org/gdalbuildvrt.html does seems very interesting. > >> As I understand it, it will do the merging part (without actually > >> merging). > > > > The VRT driver will do on-the-fly merging of tiles that have overlapping. > > The > > VRT itself is just a XML file. > > > > > >> > >> But it doesn't do the tiling part, right? > > > > No, I wasn't sure if your photos were already regularly tiled or not. > > Note that the VRT accepts non regularly tiled images. They can have > > overlapping, gaps, different resolutions, etc. The main constraints > > are : > > - they are in the same projection > > - they are "north-up", that is to say there is no rotation or skewing > > term in their geotransform matrix > > - they have the same number of bands > > > > > >> Or is the vrt so optimized tiling > >> is no longer necessary? > > > > Not necessary. Note that the VRT has no internal spatial indexing, so > > if you have several dozains of thousands of images in a VRT, it might > > slow down because it will iterate over all the image descriptions > > (without needing to open them however, all the information is in the > > VRT) to see if they intersect with the request window. But I'd expect > > the number of images in the VRT to be really high for that effect to > > become noticeable. > > > >> > >> Thanks, > >> > >> Paul > > > > 2012/7/12 Dmitry Baryshnikov <[email protected]> > > > > 12.07.2012 14:36, Paul Meems (Top-X) пишет: > > > > Thanks Even, > > > > http://www.gdal.org/gdalbuildvrt.html does seems very interesting. > > As I understand it, it will do the merging part (without actually > merging). > > > > But it doesn't do the tiling part, right? Or is the vrt so optimized > > tiling is no longer necessary? > > > > Thanks, > > > > Paul > > > > 2012/7/12 Even Rouault <[email protected]> > > > > Selon "Paul Meems (Top-X)" <[email protected]>: > > > > > >> Hi list, > >> > >> I have several aerial photos and I use MapWindow GIS to view them. > >> MapWindow is already using GDAL v1.8 > >> > >> Instead of loading each aerial photo as an individual layer I want to > >> create a local tiles store of the photos. > >> I can then just load the tiles I need based on the scale and view. > >> This will most likely improve the performance. > >> > >> The process will be something like this: > >> 1. Get the filenames of the photos > >> 2. Merge them into one > >> 3. Create tiles > >> 4. Put the tiles in a SQLite database > >> > >> My first question: Is the above suggested process correct or should I > >> do it differently? > >> My second question: What GDAL functions should I look into to > >> accomplish my process? > > > > You could try to make a VRT from all your photos. It will be seen as a > > single GDAL dataset, and will take care of the burden of opening the > > underlying photos when needed. You can use the gdalbuildvrt utility to > > create the VRT from the photos. > > > > > >> > >> Thanks, > >> > >> Paul Meems > >> The Netherlands > >> > > > > _______________________________________________ > > gdal-dev mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/gdal-dev > > > > > > > > _______________________________________________ > > > > gdal-dev mailing list > > > > [email protected] > > > > http://lists.osgeo.org/mailman/listinfo/gdal-dev > > > > There is an interesting work connected aerial imagery: > > http://trac.osgeo.org/gdal/wiki/Correlator > > http://correlatorgsoc2012.blogspot.com/ > > > > Best regards, > > Dmitry > > > > > > _______________________________________________ > > gdal-dev mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/gdal-dev > > > > > > > > > > _______________________________________________ > > gdal-dev mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/gdal-dev > > _______________________________________________ > gdal-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/gdal-dev >
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