[Proj] Polar stereographic, different values on different platforms?

Bruce Raup brauplists at gmail.com
Thu Aug 21 17:49:31 EDT 2008


On Thu, Aug 21, 2008 at 3:17 PM, Thomas Knudsen
<knudsen.thomas at gmail.com> wrote:
> 2008/8/21 Bruce Raup <brauplists at gmail.com>:
>> but the colleague I'd just introduced to all these tools is getting a
>> bad first impression of open source geospatial software (his words).
> IMHO your colleague has actually rather gotten a bad impression of Microsoft
> Compilers.

Hopefully, this is now his impression, but the *first* impression was
formed before Eric's diagnosis.  I tried to set him straight!

> Eric Miller's quick diagnosis of the cause of the problem is a wonderful
> example of what Eric Raymond dubbed Linus' law: "`Given enough eyeballs,
> all bugs are shallow". Another confirmation of the superiority of the open
> development method ("bazaar style" for proj vs. "cathedral style" for
> Microsoft's
> compilers, to follow Eric Raymond's terminology).

I agree with this general philosophy.  I can't imagine a bug being
squashed within 24 hours in a typical proprietary package.

However, I see two areas for improvement here:

1)  a rigorous test script to test the output of proj against known
correct values (within some tolerance).  It should test forward and
reverse transformations, as many of the projection/datum combinations
as is practical, using points from all eight octants of the globe.  If
this existed (and covered this particular projection), the bug would
never have been released.  I've offered to make a start at this if
this doesn't exist already.

2) Better user documentation.  At least one of the docs on the web
site is out of date (ftp://ftp.remotesensing.org/proj/OF90-284.pdf
says you can say "proj +proj=list" to get a list of projections, but
this doesn't work in any version I've seen -- I know it says it's old,
but how is a user to know what is out of date and what is not?), and
it would be good to have more examples out there to copy. A discussion
of how to treat the datum and ellipsoid separately (in cases where
they are not the same) would be particularly useful.  These issues are
even more pressing with GDAL, where the -wktext flag can affect how
the underlying proj does its job.

There are some good books out there now on some of the higher level
packages like MapServer, but I wonder if there are any efforts under
way to consolidate and expand the documentation for Proj/GDAL/OGR?  I
wish I had more time to spend on this kind of thing myself!

Bruce Raup

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