Re: [GRASS-dev] dealing with null values in rasters only within mask
Hi Moritz, On Fri, Jun 28, 2019 at 11:56 AM Moritz Lennert < mlenn...@club.worldonline.be> wrote: > > On 28/06/19 11:10, Stefan Blumentrath wrote: > > Hi Moritz, > > > > Did you consider r.stats -N for checking for NULL values within the masked area, like: > > r.stats -N input=tile,MASK > > if there is *|1 in the output you have NULL cells in the tile... the fastest way to get the total number of cells and the number of non-NULL cells, ignoring any MASK, is r.info -s, e.g. cells=4917486<-- total number of cells n=4873149 <-- number of non-NULL cells these numbers are stored in metadata and independent of the current region > > Nice trick, didn't actually know about the -N flag... > > > > > For filling NULLs with a given value you could do: > > r.mapcalc expression=tile_filled=if(MASK,if(isnull(tile),1,tile),null()) in this case, I recommend to create a custom mask that is not named MASK but e.g. mymask, and the r.mapcalc expression probably needs some modification regarding NULL values in mymask: r.mapcalc expression="tile_filled = if(isnull(mymask) != 0 and mymask != 0, if(isnull(tile), 1, tile), null())" The reason is that if(MASK, ...) should return NULL if MASK is NULL which is not what you want, you want " if MASK is not NULL" Markus M > > Duh, now that I see this, it seems quite obvious. > > Thanks Stefan ! > > (And thanks Ken for your ideas) > > Moritz > > ___ > grass-dev mailing list > grass-dev@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/grass-dev ___ grass-dev mailing list grass-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-dev
Re: [GRASS-dev] dealing with null values in rasters only within mask
On 28/06/19 11:10, Stefan Blumentrath wrote: Hi Moritz, Did you consider r.stats -N for checking for NULL values within the masked area, like: r.stats -N input=tile,MASK if there is *|1 in the output you have NULL cells in the tile... Nice trick, didn't actually know about the -N flag... For filling NULLs with a given value you could do: r.mapcalc expression=tile_filled=if(MASK,if(isnull(tile),1,tile),null()) Duh, now that I see this, it seems quite obvious. Thanks Stefan ! (And thanks Ken for your ideas) Moritz ___ grass-dev mailing list grass-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-dev
Re: [GRASS-dev] dealing with null values in rasters only within mask
Hi Moritz, More generally from Stefan's answer: 1) MASK is a raster that you can use is your r.mapcalc expressions 2) A two-step process where everything is filled, and then the parts outside the mask are re-nulled? -k. ___ grass-dev mailing list grass-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-dev
Re: [GRASS-dev] dealing with null values in rasters only within mask
Hi Moritz, Did you consider r.stats -N for checking for NULL values within the masked area, like: r.stats -N input=tile,MASK if there is *|1 in the output you have NULL cells in the tile... For filling NULLs with a given value you could do: r.mapcalc expression=tile_filled=if(MASK,if(isnull(tile),1,tile),null()) Just an idea... Cheers Stefan -Original Message- From: grass-dev On Behalf Of Moritz Lennert Sent: fredag 28. juni 2019 10:57 To: grass-dev@lists.osgeo.org Subject: [GRASS-dev] dealing with null values in rasters only within mask Hi to all, As a followup of some recent discussions concerning the handling of null values, I have a fundamental issue, and would like some feedback: I am working with irregular tiles of orthoimages. Each tile corresponds to the part of a large image mosaic that comes from a particular take. Some of these tiles contain pixels with null values (generally due to sensor saturation). I would like to be able to do the following: - detect whether there are any null values in the tile - replace the pixels values with a given value (or possibly use something like r.fill.stats) For this, I am confronted to some issues: - r.univar does not make a difference between null values in the data and those that are due to a mask (https://trac.osgeo.org/grass/ticket/3696). This means that if I create a mask to correspond to the irregular tile, I cannot use r.univar to detect whether there are any null values within the actual image tile. - If I decide to just replace all null values with a given value, r.null also does not take into account the mask. IOW, it will fill all null pixels in the entire region outside the mask with that value. - The same happens if I use r.mapcalc to replace null values with a given value. Is there any way to solve this issues with existing tools, or would this demand a change in the code, in order to differentiate null values that are null because of a mask from other null values ? Any reflections on this ? Moritz ___ grass-dev mailing list grass-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-dev ___ grass-dev mailing list grass-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-dev
[GRASS-dev] dealing with null values in rasters only within mask
Hi to all, As a followup of some recent discussions concerning the handling of null values, I have a fundamental issue, and would like some feedback: I am working with irregular tiles of orthoimages. Each tile corresponds to the part of a large image mosaic that comes from a particular take. Some of these tiles contain pixels with null values (generally due to sensor saturation). I would like to be able to do the following: - detect whether there are any null values in the tile - replace the pixels values with a given value (or possibly use something like r.fill.stats) For this, I am confronted to some issues: - r.univar does not make a difference between null values in the data and those that are due to a mask (https://trac.osgeo.org/grass/ticket/3696). This means that if I create a mask to correspond to the irregular tile, I cannot use r.univar to detect whether there are any null values within the actual image tile. - If I decide to just replace all null values with a given value, r.null also does not take into account the mask. IOW, it will fill all null pixels in the entire region outside the mask with that value. - The same happens if I use r.mapcalc to replace null values with a given value. Is there any way to solve this issues with existing tools, or would this demand a change in the code, in order to differentiate null values that are null because of a mask from other null values ? Any reflections on this ? Moritz ___ grass-dev mailing list grass-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-dev
