[GRASS-user] custom local map location

[Markus Metz]

On Sat, May 19, 2018 at 11:35 AM, Ken Mankoff <mankoff at gmail.com> wrote:
>
> Hi GRASS List,
>
> I've just spent 30 days on a field campaign collecting data. I have a
large amount of it in a GRASS mapset with location EPSG:3413. I'd like to
set up a new location with (0,0) centered on our basecamp and everything
nearby relative to that. Can someone advise how to use "proj" to create a
new location centered on either a (lon,lat) location but with units meter,
or centered on an (x,y) location from a different projection?

You could create a custom CRS based on EPSG:3413
the PROJ.4 term for EPSG:3413 is:
+proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 +x_0=0 +y_0=0 +datum=WGS84
+units=m +no_defs

now get the coordinates of the basecamp, invert the sign of the coordinates
and use these as false easting / false northing
e.g. if the basecamp is at 4000000, 5000000, use
+proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 +x_0=-4000000
+y_0=-5000000 +datum=WGS84 +units=m +no_defs

to define a custom projection centered on the basecamp

HTH,

Markus M

>
> The reason for this is so I can push data to ParaView which doesn't work
well with coordinate systems far removed from the origin.
>
> Thanks,
>
>   -k.
>
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