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I'm currently attempting to use r.region to preform analysis on a specific area of a raster image. I'm receiving Lat/Long data from the step before me, but I'm having issues using that data in r.region.

The command I'm currently running is:

r.region map=dem n=32:13:51N s=32:13:34N e=110:56:46W w=110:57:13W

Which returns the error:

`ERROR: <n=32:13:51N> ** illegal value **`

What I'm confused about is that according to the specification, this input should be legal for r.region on GRASS 6.4. According to the documentation (https://grass.osgeo.org/grass64/manuals/r.region.html) the boundaries can be specified as:

 n=value
      Value for the northern edge (format dd:mm:ss{N|S})
 s=value
      Value for the southern edge (format dd:mm:ss{N|S})
 e=value
      Value for the eastern edge (format ddd:mm:ss{E|W})
 w=value
      Value for the western edge (format ddd:mm:ss{E|W})

Why does my input fail when as far as I can tell it is in the correct format?

All the examples I've seen of r.region don't do it this way and instead do something like r.region map=mymap n=220750 s=220000 w=638300 e=639000. I would have no problem running like this except I don't understand what those values are and how to convert from lat/long (I have both DD and DMS) to this integer value.

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The issue is that you are using:

r.region map=dem n=32:13:51N s=32:13:34N e=110:56:46W w=110:57:13W

and the correct format is:

r.region map=dem n=32:13:51N s=32:13:34S e=110:56:46E w=110:57:13W

In my particular case, I tried out with:

r.region map=palma.blue n=09:30:00N s=09:27:00S w=84:07:30W e=84:07:01E

and it works perfectly; as it can be observed at the next image:

enter image description here

  • Of course its was some stupid autogenerated typo. Thanks! – Nicholas Callahan Apr 17 '16 at 19:24
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Most likely your location has a projected coordinate system (meaning coordinates in the format X-Y not Lat/Long). What does g.region -p give you? If that is the case, you can use an online converter such as this one to find the Lat/Long values for the region you want to set.

I would have written this as a comment but unfortunately reputation is too low...

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