[GRASSLIST:4323] Re: GIS visitor requests directions

Victor Wren vwren at timension.com
Mon Aug 19 15:42:04 EDT 2002

> > I cannot re-project anything to another projection. I've read and
> > re-read about setproj and numerous other commands. Can't do it.
> > Don't know what the right steps are. No idea. I've messed around
> > extensively and never got close. I've read just about everything
> > on GRASS that google reports.
> To reproject the data, first create a new location which uses the
> desired target projection. Then, from within the new location, project
> each map from the old location with r.proj, v.proj or s.proj.

As I understand this (based on the man pages and experimentation) 
this ONLY works when projecting between NAD27 and NAD83.  I have 
attempted to use this to translate points between State Plane and 
UTM coordinates (both NAD83), and the results are not good (i.e. the 
translated vectors plot about 200 miles from the region of interest).  
The documentation for ?.proj states clearly "Currently r.proj does not 
support general datum conversions. It only supports conversion 
between nad27 and nad83, and only within the CONUS conversion 
grid; 20 degrees to 50 degrees north latitude, 63 degrees to 131 
degrees west longitude. That covers all of the conterminous USA plus 
Mexico north of Mexico City and most of Canada farther south than 
Winnipeg, Manitoba." (notices for s.proj and v.proj are similar).  It 
would also appear that the source and destination MUST be in the 
same cross-section, i.e. State Plane or UTM.

I have a strong need for this, too, as I am dealing with several sources 
of data, mostly in UTM (NAD27 and NAD83) State Plane (NAD83) and 
Geo coordinates, but the customer requires State Plane (NAD83) for 
the final product (and being in the USA, the data is a complete mix of 
feet and meters).  Fortunately all of my data is within Colorado Central, 
but ?.proj does not appear, currently, to be useful for world maps, or 
for GEO coordinates of any kind.

This is my experience with G5-pre5

Victor Wren

More information about the grass-user mailing list