Hello,
Is anyone a mercator projection location with GRASS?
I am trying to create a new location in a mercator
projection and I am not having much luck.
In setting up the new region, GRASS asks me for the
units and a conversion factor to meters. The units
for a mercator projection are degrees. Does GRASS
convert the degrees to meters? And the conversion
factor is different for lat and lon. I am confused.
Has anyone successfully done this?
Thanks.
-Stephen Dzurenko
Ocean Mapping Division
Ocean Technology Center
Graduate School of Oceanography
University of Rhode Island
ph: 401 792-6853
fx: 401 792-6849
e-mail: steve@ocean.oce.uri.edu
"Steve" == Steve Dzurenko <steve@ocean.oce.uri.EDU> writes:
Steve> Hello,
Steve> Is anyone a mercator projection location with GRASS? I am
Steve> trying to create a new location in a mercator projection
Steve> and I am not having much luck. In setting up the new
Steve> region, GRASS asks me for the units and a conversion factor
Steve> to meters. The units for a mercator projection are
Steve> degrees. Does GRASS convert the degrees to meters? And
Steve> the conversion factor is different for lat and lon. I am
Steve> confused. Has anyone successfully done this?
Steve> Thanks.
Steve> -Stephen Dzurenko
Steve> Ocean Mapping Division
Steve> Ocean Technology Center
Steve> Graduate School of Oceanography
Steve> University of Rhode Island
Steve> ph: 401 792-6853
Steve> fx: 401 792-6849
Steve> e-mail: steve@ocean.oce.uri.edu
Steve,
I've digitized, in GRASS 4.1.3, some NOAA charts which used the
Mercator projection. When setting up the GRASS location, I specified
the `merc' projection and GRASS asked me for an ellipsoid, a ``Central
Meridian'', and a ``Latitude of True Scale'' (these are in quotes
because I'm not sure what they mean). I used the *default* central
meridian and the ellipsoid and latitude of true scale specified on the
chart. After all that, it asked be for the ground units, which I
chose to be meters. I was later able to reproject the digitized charts
into UTM and state plane coordinates without difficulty. I can't tell
you how GRASS deals with the projection internally, but for me it
seemed to work.
Hope this helps.
Bill.
--
Bill Perkins
Battelle Pacific Northwest Laboratories
Environmental Sciences Center, Subsurface Flow and Transport
P.O. Box 999 MSIN K9-36
Richland, Washington, USA 99352 (509) 372-6131
wa_perkins@pnl.gov