[GRASSLIST:2178] Re: Projection questions

[Rich Shepard]

On Fri, 27 Jul 2001, Frank Warmerdam wrote:

> > unit: unknown
> > units: unknowns
> > meter: 1

> The "unit" value is the singular name for the linear unit.  The "units" value is
> the plural.   The "meter:" value is the size of this unit in meters.  Since this
> value is 1.0 we see that it is really in unit meters but r.in.gdal isn't
> establishing this correctly.

Frank,

  Thanks very much. Just to confirm my understanding. If the map is
projected in State Plane Coordinates/NAD27, then the file would read:

unit: foot
units: feet
meter: 0.3048

  Correct?

  When you write that r.in.gdal "isn't establishing this correctly", do you
mean that it's just not writing the PROJ_UNITS file correctly?

> > proj:       1

> The association of 1 with UTM is "in the code", and not controlled by any
> configuration files.  GRASS programs that report on projections should
> know how to translate into human readable form.

  Hmm-m-m-m. I think we're getting to another question here. That's good, by
the way. :-)

  I'm reorganizing my entire data structure to make GRASS5 happy (I'm told
the existing structure should work, but my problems with r.in.gdal+r.proj
prove otherwise). As most of my current projects are in the Pacific
Northwest of the U.S., I'm setting up a top-level location called PERMANENT
that defines the boundaries of this left third of the country. The
projection is Albers Equal Area (aea on the /usr/local/grass5/etc/prjections
file list). How do I specify that in a numeric equivalent?

  I know that '99' is used for both 'user specified' and 'spc', but I cannot
find a list of codes for other projections.

  And, can we assume that all GRASS modules that work with/report on
projections know what the projection is? If this is the case, do we need to
specify it in the PROJ_INFO file?

Stumbling toward understanding,

Rich

Dr. Richard B. Shepard, President

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