[GRASSLIST:1158] Re: Converting DRG Albers to UTM

Morten Hulden morten at ngb.se
Mon Nov 20 13:46:26 EST 2000

Hi Jeshua,

I noticed no one had responded to this on the list yet, so I throw in some
general ideas

Try to create a location corresponding to the projection of the map/data
to be imported. You may need to know a lot a parameters to create that
location. If you don't have them you can always create an XY-location (and
maybe later manually change the PROJ_INFO and DEFAULT_WIND files in the
PERMANENT subdirectory for that location) This will at least let you view
the imported map in the grass monitor (which _may_ give some more hints
about missing parameters).

> So would I set up my database in UTM or Albers?  

In Albers (Equal Area) first. Then import to that location. Then create
the UTM location you want and convert the map to that location. You have
to quit from grass and restart it in order to create/switch locations.
Remember that with each conversion some data is lost, so keep the Albers
location around so you have access to the original data in case you want
it into some other projection later.

>  1st standard parallel        34 00 00      (would this be 34N?)
>  2nd standard parallel      40 30 00
>  Central Meridian             -120 00 00    (would this be entered as 120W or -120 ?)
>  Latitude of Origin              00 00 00

g.setproj accepts either hexagesimal (120:30:00W) or decimal
(-120.5) format.

> Does anyone know how I can figure out what the value for the Central
> parallel?

Latitude of origin = Central Parallel is usually but not necessarily 
midway between the the 1st and 2nd standard parallels. The zero value
above is incorrect, try 37N.

Use one of the 'in' tools to import, then switch to the UTM location 
and use r.proj and v.proj to convert the maps. (r.proj may not work
properly for all projections but there is a replacement r.proj.new in the
CVS repository)

hope this helps

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