[OSRS-PROJ] Lambert Conformal Conic 1SP
Gerald I. Evenden
gerald.evenden at verizon.net
Sat Feb 8 16:17:12 EST 2003
My only comment at the moment is that I am surprised that no scale
parameter was used as that is usually the compensating factor for
using the tangential form versus the secant form.
Since I finally got ol' PROJ on my system a month or so ago I will
have to load it in and give your numbers a try.
Obviously, a couple of meters is not tolerable in any situation.
Bench mark data set are important provided they are well certified
by a *large* number of knowledgeable cartographers. Unfortunately,
I have come across few such sets.
On Sat, 2003-02-08 at 14:32, Frank Warmerdam wrote:
> 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:
> or the section on LCC 1SP excerped at:
> 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,
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