[GRASSLIST:3206] Re: bathymetry

[Brent Wood]

On Sun, 18 Apr 2004, Hamish wrote:

> > I am using GRASS 5.0.0 on a mac (10.2.8).  I am not sure what you mean
> > by datum support.
>
> for a better explanation than I could give you, see:
> http://biology.usgs.gov/geotech/documents/datum.html
>
>
> > I thought that I specified the datum for a location
> > when I set it up.  Do you mean that I can not project across datums
> > when using a command like r.proj?
>
> Not with GRASS 5.0.0, maybe there is limmited NAD27 and NAD83 support?
> Someone else would have to answer that, but generally no; you need a
> newer version of GRASS for r.proj to handle transformations between
> different datums correctly.

But you can export the data, & run it through the cs2cs program manually.
This is a part of the proj package (the same one GRASS uses to manage
reprojection).

>From the man page:
       Cs2cs performs transformation between the source
       and destination cartographic  coordinate  system
       on a set of input points.  The coordinate system
       transformation can include  translation  between
       projected  and geographic coordinates as well as
       the application of datum shifts.



After reprojecting it (with the datum shift) you can create a new GRASS
mapset for the new projection and import the data.

I don't believe you can overlay data from different mapsets on the fly
though.


Brent Wood