Thanks Alex for your help here. I keep this in mind for next time. Michael
2014-04-29 5:41 GMT+02:00 Alex Mandel <[email protected]>: > GDALInfo "Band NODATA value. " if known. In the case where it's not set > in the header of the file then you have visually inspect the raster > using the info tool to figure out what nodata is in use. Generally all > rasters in the same set from a given source use the same nodata (for > batching purposes). > > Then you can use GDAL_Translate to assign -a_nodata value: > > Thanks, > Alex > > On 04/28/2014 10:27 AM, kimaidou wrote: > > Hi Andreas > > > > About no data, I tried many things with no luck : NULL, none, 0, etc. If > > someone knows, please help (and update documentation if possible). > > > > I would like to change the nodata value, but could not find any way. It > > seems Grass can do it via the r.null alg, but it is not yet in > Processing. > > Some tools in QGIS, related to GDAL, seem to be able to replace a know > > nodata value into another one. But it is often a chicken and egg problem, > > since we do not always know the nodata value (or I am missing some other > > tools like command line gdal to get it ?) > > > > Cheers > > Michael > > > > > > 2014-04-28 16:26 GMT+02:00 Andreas Neumann <[email protected]>: > > > >> Hi, > >> > >> Again on the raster calculator: I noticed that nodata raster cells > >> cannot be detected. They seem to be ignored. Is there any trick to query > >> nodata cells? They are explicitly set to nodata, not to 0. > >> > >> Andreas > >> > >> Am 24.04.2014 12:57, schrieb Carlos Cerdán: > >>> Hi Andreas: > >>> > >>> Yes, it always evaluates to true because of "OR" condition , so try: > >>> > >>> (lake_mask > 0) * lake_mask + (lake_mask<=0)*dtm > >>> > >>> Good luck > >>> > >>> Carlos > >>> > >>> > >>> > >>> > >>> 2014-04-24 1:53 GMT-05:00 Andreas Neumann <[email protected]>: > >>> > >>>> Hi, > >>>> > >>>> I have a hard time understanding the raster calculator syntax. > >>>> > >>>> I would like to merge two rasters: DTM and lake mask. Let's call the > one > >>>> dtm and the other lake_mask. > >>>> > >>>> When the lake_mask has a value > 0 then I would like to take the value > >>>> of the lake_mask, otherwise the value of the dtm. > >>>> > >>>> What would an appropriate syntax look like? > >>>> > >>>> I tried something along > >>>> > >>>> ((lake_mask > 0) * lake_mask) OR dtm > >>>> > >>>> But all I get in the resulting grid are values of 1. I guess it is > >>>> because it always evaluates to true? > >>>> > >>>> Thanks for your help. > >>>> > >>>> Andreas > >
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