[GRASSLIST:3494] Re: NMEA log to GRASS vector?

[Andreas Lange]

Hi James,

James Cameron wrote:
> 
> On Wed, Apr 10, 2002 at 12:21:19PM -0700, Alejandro Hinojosa wrote:
> > I handle NMEA sentences and waypoint downloads with awk scripts to import
> > them to grass or whatever.
> 
> Just what I needed, thanks.
> 
> > The file generated can be imported throgh v.in.ascii then projected to
> > whatever with v.proj.
> 
> Ah, I think this is my next question ... given that my existing location
> is in UTM using Australian Geodetic 1966, and the NMEA log conversion
> gives me latitude longitude using WGS 84 ... how do I proceed?
> 
> I've read the manual pages for v.proj, g.setproj, and I've verified my
> datum is in the datum.table, but I don't want to break anything.

Currently the datum shift is not implemented in GRASS. The datum from
the reference table (datum.table) is stored when the new location is
created with g.setproj, but the datum info is never used by GRASS. e. g.
the {v|r|s}.proj commands do not use them. Its just recorded for upward
compatibility. You may add your datum settings manually to PROJ_INFO,
but be careful, you are on your own. 

> 
> Do I run g.setproj to add the datum to the location?  I get a warning
> that suggests I should not do this.  I think I'm confused and uncertain.

I would recommend to install proj.4 (external to grass) and use proj
(from scripts) to project and datum shift your NMEA data to the settings
of your location (UTM/Australian Geodetic 1966). 
I worked on a more general solution for importing GPS waypoints (with
tcl scripts), but due to problems with the GRASS projection system i do
not plan to release this. 

HTH,

Andreas
-- 
Andreas Lange, 65187 Wiesbaden, Germany, Tel. +49 611 807850
url: http://mitglied.lycos.de/AndreasLange
mail: Andreas.Lange_at_Rhein-Main.de - A.C.Lange_at_GMX.net