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
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