[GRASS-user] xy to lat long

Hamish hamish_b at yahoo.com
Mon Sep 26 20:27:40 EDT 2011

Raphael wrote:
> > i have imported the etopo dem (geotifff) into grass.
> > It appears to be in XY and i would like to convert
> > these to lat longs.

> I looked at
> http://grass.osgeo.org/wiki/Global_datasets#ETOPO_.28DEM.29
> and was surprised to see the XY thing there for ETOPO1.

there are two versions available. note the ETOPO-1 wiki section
starts with "The cell registered version can be loaded directly
into a lat/lon region."   That one will load directly into the
lat/lon region; I've bolded that text now.

but the NOAA site states "The grid-registered is the
authoritative registration. The cell-registered is derived from
the grid-registered, and the conversion produces slightly
flattened relief. More about grid registration:
 http://www.ngdc.noaa.gov/mgg/global/gridregistration.html "

I think the "import into XY, crop outer edge & recenter" before
converting the XY location into a lat/lon loc'n hack was written
before the 'r.in.gdal -l' flag + fix with r.region came to be
(perhaps because of?), and since these datasets need r.in.bin
you'd need to compose a gdal .vrt file describing the byte order
etc to use r.in.gdal?

> But in any case the ETOPO2 will be better (see wiki for an
> article how to import it).

yes for ease of import, but not so much for modernity. 
"Historic ETOPO2v2 and ETOPO5 global relief grids are deprecated
but still available."

for ETOPO2 the authoritative registration was cell-centered, which
is the same as GRASS uses, so everything lines up and it's a lot


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