not shure if it's the same... not sure if the requests are for band statistics or background image prefetch of an extended canvas view (introduce 1y ago if I well remember)
you can simply check if bandSatatisti is available or triggered doing it with (ir R is the QgsRasterLayer) renderer = R.renderer() renderer.hasStatistics(1) # True or Flase; 1 is the band number stat = bandStatistics(1) # this would trigger remote reading if false step before bandStatistic is a QgsRasterInterface (e.g. the provider), so any provider can implement statistic calc in different way... Luigi Pirelli ************************************************************************************************** * LinkedIn: https://www.linkedin.com/in/luigipirelli * Stackexchange: http://gis.stackexchange.com/users/19667/luigi-pirelli * GitHub: https://github.com/luipir * Mastering QGIS 2nd Edition: * https://www.packtpub.com/big-data-and-business-intelligence/mastering-qgis-second-edition * Hire me: http://goo.gl/BYRQKg ************************************************************************************************** On Fri, 18 Jan 2019 at 14:34, Richard Duivenvoorde <[email protected]> wrote: > Hi Luigi, > > I cannot be of help, but I think I had exactly this problem then you, > when there is a OGC-WCS service with for example a huge DEM/height model. > > And after that QGIS is requesting several times for one extent some > portion of the data (while this server is very slow on this) > I was thinking about a possibility to NOT do this everytime (or at least > give an option to do it ONLY on the real data available already by QGIS). > > Does this fit your problem? > > Regards, > > Richard Duivenvoorde > > ps anybody willing to play with such a dem: > > > https://geodata.nationaalgeoregister.nl/ahn3/wcs?request=GetCapabilities&service=wcs&version=1.1.2 > > (epsg:28992) > > On 1/18/19 1:56 PM, Luigi Pirelli wrote: > > Hi devs > > > > I face a (IMHO) an API limitation that I'm not sure is a limitation of a > > feature :) > > > > I'm working adding SLD export for rasters as new feature and some > > stretching (QgsContrastEnhancement) should be mapped differently if the > > min/max values has been modified from the real min/max of the image. > > > > This can be simply asked to the raster with > > QgsRasterLayer.statistic(<band number>). The main problem I'm faced is > > that if statistic is not present it is ALWAYS calculated. > > This means that if we have big images or a remote one (e.g. COG) this > > would take long time! > > I do not analysed any raster provider, but I suppose that min/max values > > can be estimated asking to raster metadata. > > > > IMHO we can have an API like > > QgsRasterLayer.estimatedStatistic(<band number>) > > or > > QgsRasterLayer.statistic(<band number>, estimated=false) > > > > that can return metadata values if available. > > > > The proposal is valid if there is no a method to get estimated > > statistic, but I could be wrong and that's the reason of this post. > > > > Luigi Pirelli > > > > p.s. remember to come to 2019.qgis.es <http://2019.qgis.es> ;) we'll > > open inscription next monday! > > > > > ************************************************************************************************** > > * LinkedIn: https://www.linkedin.com/in/luigipirelli > > * Stackexchange: http://gis.stackexchange.com/users/19667/luigi-pirelli > > * GitHub: https://github.com/luipir > > * Mastering QGIS 2nd Edition: > > * > > > https://www.packtpub.com/big-data-and-business-intelligence/mastering-qgis-second-edition > > * Hire me: http://goo.gl/BYRQKg > > > ************************************************************************************************** > > > > _______________________________________________ > > QGIS-Developer mailing list > > [email protected] > > List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer > > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer > > > > _______________________________________________ > QGIS-Developer mailing list > [email protected] > List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
_______________________________________________ QGIS-Developer mailing list [email protected] List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
