Hi there, and thanks for the replies! Those got me into the right direction... even though there are a few snags in qgis (see end of message).
What I ended up doing: 1) create graticule using gdaltindex - this will serve only as a visual guide to the user 2) create a vrt catalog using gdalbuildvrt 3) edit the vrt file manually to insert band statistics - so the vrt will load fast in qgis 4) create a mosaic with 25x bigger pixel resolution (2.5m) 5) build overviews for the mosaic 6) create a qgis project where the mosaic is visible until 1:9000 scale is reached 7) edit the qgis project manually to set the minimum visibile scale of the vrt catalog to 1:9000 This got me a pretty good performance. I could even load 2 sets of images instead of just 1, with a total of 880 ecws. (Note that qgis gets hold of ~1GB ram in my pc.) Now there are 2 problems in QGIS that I detected or confirmed: 1) if a vrt file does not have statistics, qgis hangs while loading the vrt file. You have to add statistics to the vrt. To make it faster I create a small vrt with a few ecws and built the statistics using gdalinfo -stats. Then copied those statistics into the big vrt catalogs. 2) QGIS will hang on opening the properties of a vrt catalog, I assume when it's big enough... couldn't find the reason. So to change the properties of these layers I had to save the project and edit manually. I suspect the problem could be qgis is building the histogram... but could not find a way to confirm. After this experiment I feel a somewhat simple requirement gets really complicated, not because the software couldn't handle it but because there are few loopholes (2) to solve in qgis in this particular area - big raster. Hope this is helpful to someone else, and that the devs pick this up too ;) Duarte -- View this message in context: http://osgeo-org.1560.n6.nabble.com/qgis-and-big-raster-catalogs-tp4672179p4715613.html Sent from the Quantum GIS - User mailing list archive at Nabble.com. _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
