From my experience, GeoTIFF has a long history and is a more appropriate format to handle multiple large rasters. As a container, it could handle misc compression format (JPEG an other), misc representation at different scales (resolution is not a problem), misc color modes with raster/vectorial alpha layer, and so on. In one of my projects I handle more than 400 raster files (4000x4000x32) without any problem. Of course, a better and final choice would be to tile everything, but it is sometimes difficult with older maps.
Le lun. 18 nov. 2019 à 10:12, Patrick Dunford <enzedrailm...@gmail.com> a écrit : > > Good day to all > > One of the user experiences I have had from using the Qgis software has been > with projects using large numbers of raster tile layers. These layers are > generally tiles that have a size of 4800x7200 pixels in GeoJPEG format and > have either been downloaded directly from tile servers to these locally > stored files, or created from downloaded tiles with other layers overlaid in > Gimp projects. > > There appears to be some architectural limit in Qgis desktop software > relating to either the total number of raster layer [files] in a project or > to the total number of pixels in raster layer [files] in a project. This is > unrelated to the number of layers or pixels currently enabled for display in > the map canvas. In practice, the appearance of this limit is that it is > kicking in long before the host computer's own physical resources are > anywhere near fully engaged. Map digitising and editing is done on systems > with 32 GB of physical memory (RAM) and 200 GB of SSD-based virtual memory > (swap) and these systems are able to edit very large Gimp projects for user > tile creation that often engage all of the system's physical memory and > around 100 GB of the virtual memory without problems. But these types of > numbers are in practice never seen with Qgis projects when the raster layer > limit is being seen. > > The appearance of a raster layer limit is generally experienced in older > versions of the software by layers being displayed on the canvas as garbage, > and in newer versions by the software crashing. It will only start working > again if raster layers are removed from the project. However, when layers are > loaded from WMTS servers, no appearance of limitation is seen. > > The question to be answered, then, is which of any possible range of > resolutions would be appropriate or useful to this predicament. With only > limited understanding of the architectural design of the software, it would > seem the following options exist: > > File a bug report for the software concerning a possible issue with the > design of the product > Amalgamate smaller tiles into larger ones (e.g. 48 tiles at 4800x7200 can be > put into one tile at 57600x28800). This only works if the software issue is > related to the number of file based tile layers and not to the total number > of pixels in those layers. > Post a feature request for sub-project capabilities. This would allow a > project that combines vector and raster layers, to be split into one project > containing the vector layers and a number of projects each of which contains > the vector project as a subproject and a certain subset of all the raster > layers that is smaller than the observable limit. > Set up my own local WMTS server to serve all the raster layers to my map > editing projects. > Explore the possibilities of preconfigured limits in the operating system > that may need to be increased to overcome file based layer limits in projects > (such as the NOFILES limit in Linux, currently set at 10,000 hard and soft on > map editing computers) > > Is anyone who is knowledgeable about the architecture of the Qgis desktop > software able to comment with some detail about possible resolutions. > > > _______________________________________________ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
