[GRASS-user] region settings

[Daniel Lee]

Hi Janet,

Tthe data seems to be in a geographic (angular) coordinate system, which
means that you won't be able to get resolution in meters. Due to the
curvature of the Earth's surface, one arc second has a different length at
different latitudes. That's exactly what you're seeing in your example -
0:00:01 means 0° 0" 0'. The notation is in degrees minutes seconds (DMS)
rather than decimal degrees (DD), which I prefer, but however you look at
it, unless you reproject the data into a projected coordinate system like
UTM, etc., the resolution will be in that unit.

The short version of that long story is that your data sounds like it's
fine - 1 arc second is about 30m and so it looks like you've got the data
you wanted and GRASS interpreted it correctly.

Best,
Daniel

--

B.Sc. Daniel Lee
Geschäftsführung für Forschung und Entwicklung
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2012/8/8 Janet Choate <jsc.eco at gmail.com>

> Hi all,
> this seems silly, but i am a bit confused as haven't had this be an issue
> before.  i downloaded data from USGS NED (they have changed the process
> since i last used). i requested data at 1 arc second (which is supposed to
> be approx 30 meters)
>
> i set up a new grass dataset, reading the projection and datum terms from
> a georeferenced data file (referring to the w001001.adf file).  at the 'set
> default region extent and resolution' page, the correct N/S/E/W coordinates
> are shown, however, the N-S & E-W resolution are set to 0.000277777777841.
>  it would not let me change the resolution.  accepted and set the region.
>  then used r.in.gdal to import the raster (the w001001.adf file), then set
> the region to the new dem raster and displayed it.  so all seemed to work
> fine.  however, when i check the region settings with g.region -p, the
> nsres/ewres are 0:00:01.
> i need this to be a 30 meter DEM, and am confused as to what the present
> resolution actually is, as i requested 30m (1 arc second) at download from
> NED.
> anyone have any tips regarding this?
>
> thank you,
> Janet
>
>
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