[OSRS-PROJ] Lambert Conformal Conic 1SP

[Frank Warmerdam]

Folks,

I have found what I believe to be an inaccuracy in the LCC 1SP support in
PROJ.4, and I wonder if anyone has any comment on possible solutions.

As an example, using this commandline:

proj +proj=lcc +lat_1=18 +lat_0=18 +lon_0=-77 +k_0=1 +x_0=250000 +y_0=150000 
+ellps=clrk66 +units=m

And input:

76d56'37.26"W 17d55'55.80"N

I get this output:

255968.19       142493.14

The coordinate system is EPSG 24200 - JAD69 / Jamaica National Grid and is
used as an example in the EPSG paper "Guidance note #7" available at:

   http://www.remotesensing.org/geotiff/proj_list/guid7.html

or the section on LCC 1SP excerped at:
   http://www.remotesensing.org/geotiff/proj_list/lambert_conic_conformal_1sp.html

Looking there we see the result should be (255966.58, 142493.51).  The error
is a couple of meters.  Not outragous, but significant, and plenty to trip
up my autotests.

I have run the same coordinate system through the FME software (based on the
projections engine from Mentor Software and it matches the EPSG results to
a centimeter or better.

Is it possible the problem is with using a general LCC formula for the 1SP
case when there is a more precise way of handling that?

By the way, this has come up as I am refining support in FME for coordinate
systems derived from EPSG.  As part of this effort I have produced a test
file of reference points for every projected coordinate system and the expected
result when reprojected into lat/long.  I generated the test file using PROJ.4
(bound within OGR) and then run it again using the FME projections engine.

It is my thought that such a test suite of known points could be useful for
validating other projection engines as well ... with the caveat of course that
PROJ.4 isn't "the master", but if differences are found it suggests the
need for further manual examination.

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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