[OSRS-PROJ] Lambert Conformal Conic 1SP
Gerald I. Evenden
gerald.evenden at verizon.net
Sat Feb 8 17:54:43 EST 2003
I compiled and loaded PROJ on my RedHat Linux system, edited your
email into a script and executed it:
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 <<EOF
76d56'37.26"W 17d55'55.80"N
EOF
produces:
255966.58 142493.51
These numbers seem to match the JAD69 / Jamaica National Grid
numbers in the referred to web page.
You seem to have a flawed version of proj.
However, I do agree that there should be a set of standards
which can be used to test installations of any cartographic
projection system. I do have a set of numbers which I got
from NMD which can be used to verify SPCS conversions. But
material for foreign systems is lacking in my shop.
On Sat, 2003-02-08 at 14:32, Frank Warmerdam wrote:
> 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, ...
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