LL projection

[Jill Schuler]

The following is a response to Jerry's soapbox:

%%%In the Gardner/Schuler discussion a "latitude-longitude" projection
%%%is mentioned which appears to be equivalent to the proper and more
%%%descriptive names of Equidistant Cylindrical, Equirectangular or Plate Caree.
%%%Thus we have added one more level of confusion to an already confusing
%%%situation.  To add to the confusion, the name is derived from the
%%%names of the axis of a coordinate system.


The latitude-longitude name is a GRASS reference.  CERL chose to name the
Equidistant Cylindrical projection as "ll" hence the discussion of latitude-
longitude as a projection.  The proper name for this projection should be used
by GRASS (i.e., eqc and the PROJ_INFO file should also record the correct
values for "a" and "es").  I can not make this change, I can only recommend
this change to CERL.  Life would be simpler if we all conformed to the 
same naming conventions especially since GRASS IS using MAPGEN'S proj.  
Additionally,  I strongly suggest that GRASS'S ellipsoid names follow suit too!
Mapgen calls Clark66 "clrk66" and GRASS refers to the same ellipsoid as
"clark66".  Every ellipsoid referenced in GRASS has a different name then
what MAPGEN supports.

%%%But what has happened, is that wrapper scripts, in a laudable effort 
%%%to simplify usage, tend to emasculate the flexibility of the system.

%%%In this case, I shudder to think that +proj=eqc can't be used and "MAPGEN"
%%%gets a reputation for not being able to handle a common projection
%%%(that it can under different usage circumstances).
%%%

The previous discussion did not suggest limitations with MAPGEN or the mapdef
program--or even in the Interface.  The problem lies totally with GRASS and its
lack of conformity to the standard naming conventions used in MAPGEN and the
inconsistent structure of the PROJ_INFO file.  

The current MAPGEN Interface fully supports every projection used by proj.  
The make.mapdef script offers the user a default projection based on the 
GRASS projection recorded in the PROJ_INFO file or allows the user to select 
a projection from MAPGEN.  

The projection list option in the Interface is actually running the proj 
command "proj -lp".  Additionally, because the GRASS "ll" projection IS NOT 
a known projection name in MAPGEN, the Interface forces the user to select 
a VALID projection name for the mapdef program.

There really is no official communication vehicle for MAPGEN.  For the past
five years I have handled the help desk for "SCS" and other federal callers.
Email messages about MAPGEN are posted to the GRASS User's list and I respond
to these also.

Currently, we are in a transitional period.  All software development and
support are being transfered to Ft. Collins, CO.  This seems to be the ideal
time to develop "a better communication mechanism" for the MAPGEN system.
What does the user community need??? Give me some feedback on this issue.

I am not on the normal distribution list for the grass user's bb so please
email me directly.  Most mapgen questions are forwarded to me via ken or
hanh.

Regards to all,


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#  # #### #### ####      ######  #### ##### Jill R. Schuler
#  # #    #  # #  #      #      #     #     USDA 
#  # #### #  # #### ### ####   #     ####   Soil Conservation Service
#  #    # #  # #  #        #  #         #   National Cartography and 
#  #    # #  # #  #       #  #         #    GIS Center
#### #### #### #  #   ####  ###### ####     P.O. Box 6567 
				            Ft. Worth, TX 76115
e-mail: jschuler at ncg.scs.ag.gov             Phone: (817) 334-5559 x3086

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