[OSRS-PROJ] Prime Meridian Support in PROJ.4 - Philosophy !!

Clifford J Mugnier cjmce at lsu.edu
Thu Oct 3 17:43:52 EDT 2002

When the late John P. Snyder and I started corresponding, cartography was
still just a hobby for the Chemical Engineer and datum transformations were
an oddity in Geodesy that was rarely encountered outside of Military
Geodesy.  The Navy Transit Doppler satellite program was still classified
(WGS72), and every country in the world was still doing classical geodesy
with theodolites except for the militaries of the U.S., U.K., Canada, and
Australia.  The "distinction" between Cartography & projections versus
Geodesy and datums was quite clear.

Times have changed, and "GIS" people don't only want to work in one
reference frame - the digitized paper map.  People want to make a
connection between their digitized/scanned data and stuff they can gather
themselves with a shirt-pocket satellite receiver.  People have always
wanted to do that sort of thing; the difference is that they can now go out
and purchase the hardware tools that are in stock on someone's store shelf!

Times change, and old traditions (and software) must yield to reality or be
left in the dust.


Prof. Clifford J. Mugnier (cjmce at LSU.edu)
Chief of Geodesy
Department of Civil Engineering
Baton Rouge, LA  70803
Voice and Facsimile:  (225) 578-8536
Pager:              1-(888) 365-5180

Gerald Evenden wrote:
> Just as an aside from the original author of proj.4:  prime meridian has
no place
> in proj.4.  Any offsets in longitude due to variations in coordinate
system "prime
> meridian" should be taken care of externally with adjustments to "lon_0"
> parameter.


Certainly this is how people have dealt with this issue in the past, and it
works fine when PROJ.4 is just used for projections.

> My probem is that I view the projections and their math as pristene
entities  and
> not disturbed with regtional egos and their arbitrary orientations of
> systems.
> I know my advice will be ignored but I could not resist expressing my
> with the inclusion of PM code within the proj.4 library.  PMS, if you

Well, the corruption started when I introduced support for converting
between different datums. At that point I was trying to make PROJ.4 into
a coordinate system conversion library rather than just a projections
library.  I can see why you feel that is a perversion of the original
of PROJ.4, and the focus of it's role, but that is the danger of open
Your work can be adopted an taken in directions you never intended.

That said, I think PROJ.4 is serving an important function for lots of
projects by taking on the larger role of coordinate systems conversion and
that integrating that task in one library rather than two layered libraries
has some benefits.

Your advice isn't exactly disregarded ... your vision messages cause me
lots of
angst!  It just that user demand (and my own needs) has led me to take
in a different direction than originally intended.  Obviously we all owe
alot as you did all the hard work ... the stuff that I am far from
to do.  But in the end, I will still pursue the features I think are useful
and needed.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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