[GRASS-user] Patching rasters based on other rasters

GRASS GRASS user
1

Dear GRASS List,

I'm trying to do something in GRASS and can't figure out an efficient way to do it. I'm guessing it is possible with 1-3 lines, but don't know which ones. The algorithm I'm developing would be much more complex, and I hope someone can suggest a shortcut.

I have several satellite products of the same region each day. For simplicity sake lets assume 3 overlapping solar zenith angle (SZA) products, and for each of those a visual image (VIS). I'd like to have one visual raster that, for each pixel, has the minimum SZA.

I can get the minimum SZA for each pixel with

r.mapcalc "SZA_min = min(SZA1,SZA2,SZA3)"

But now I've lost the source of the minimum SZA, and I need it to link SZA1 with VIS1.

I could encode categories for each SZA:
r.category map=SZA1 cats=0-360 values=1
r.category map=SZA2 cats=0-360 values=2
r.category map=SZA3 cats=0-360 values=3

And then

r.mapcalc "SZA_min_cat = min(@SZA1,@SZA2,@SZA3)"

And then use SZA_min_cat (values: 1 to 3) as a lookup to VIS1,VIS2,VIS3. I'm actually not clear how to do this last step, if this is the correct approach. Do I return to r.mapcalc, or is r.univar the right tool?

Any help will be much appreciated.

Thanks,

  -k.
  

2

Le 17 octobre 2017 13:38:34 GMT+02:00, Ken Mankoff <mankoff@gmail.com> a écrit :

Dear GRASS List,

I'm trying to do something in GRASS and can't figure out an efficient
way to do it. I'm guessing it is possible with 1-3 lines, but don't
know which ones. The algorithm I'm developing would be much more
complex, and I hope someone can suggest a shortcut.

I have several satellite products of the same region each day. For
simplicity sake lets assume 3 overlapping solar zenith angle (SZA)
products, and for each of those a visual image (VIS). I'd like to have
one visual raster that, for each pixel, has the minimum SZA.

I can get the minimum SZA for each pixel with

r.mapcalc "SZA_min = min(SZA1,SZA2,SZA3)"

But now I've lost the source of the minimum SZA, and I need it to link
SZA1 with VIS1.

I could encode categories for each SZA:
r.category map=SZA1 cats=0-360 values=1
r.category map=SZA2 cats=0-360 values=2
r.category map=SZA3 cats=0-360 values=3

And then

r.mapcalc "SZA_min_cat = min(@SZA1,@SZA2,@SZA3)"

And then use SZA_min_cat (values: 1 to 3) as a lookup to
VIS1,VIS2,VIS3. I'm actually not clear how to do this last step, if
this is the correct approach. Do I return to r.mapcalc, or is r.univar
the right tool?

Any help will be much appreciated.

Check r.series, notably the min_raster method.

Moritz

Thanks,

-k.

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3

Thanks. That helps. I now use the output of that (SZA_lut) and the following:

r.mapcalc --o <<EOF
eval(SZA0 = if(SZA_lut == 0, ${img_arr[0]}),
SZA1 = if(SZA_lut == 1, ${img_arr[1]}),
SZA2 = if(SZA_lut == 2, ${img_arr[2]}),
SZA3 = if(SZA_lut == 3, ${img_arr[3]}),
SZA4 = if(SZA_lut == 4, ${img_arr[4]}),
SZA5 = if(SZA_lut == 5, ${img_arr[5]}))
SZA_min = SZA0+SZA1+SZA2+SZA3+SZA4+SZA5
EOF

-k.

···

On Tue, Oct 17, 2017 at 1:41 PM, Moritz Lennert <mlennert@club.worldonline.be> wrote:

Le 17 octobre 2017 13:38:34 GMT+02:00, Ken Mankoff <mankoff@gmail.com> a écrit :

Dear GRASS List,

I’m trying to do something in GRASS and can’t figure out an efficient
way to do it. I’m guessing it is possible with 1-3 lines, but don’t
know which ones. The algorithm I’m developing would be much more
complex, and I hope someone can suggest a shortcut.

I have several satellite products of the same region each day. For
simplicity sake lets assume 3 overlapping solar zenith angle (SZA)
products, and for each of those a visual image (VIS). I’d like to have
one visual raster that, for each pixel, has the minimum SZA.

I can get the minimum SZA for each pixel with

r.mapcalc “SZA_min = min(SZA1,SZA2,SZA3)”

But now I’ve lost the source of the minimum SZA, and I need it to link
SZA1 with VIS1.

I could encode categories for each SZA:
r.category map=SZA1 cats=0-360 values=1
r.category map=SZA2 cats=0-360 values=2
r.category map=SZA3 cats=0-360 values=3

And then

r.mapcalc “SZA_min_cat = min(@SZA1,@SZA2,@SZA3)”

And then use SZA_min_cat (values: 1 to 3) as a lookup to
VIS1,VIS2,VIS3. I’m actually not clear how to do this last step, if
this is the correct approach. Do I return to r.mapcalc, or is r.univar
the right tool?

Any help will be much appreciated.

Check r.series, notably the min_raster method.

Moritz

Thanks,

-k.

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