[Proj] Parsing Lambert Conformal Conic in GDAL

Kyle Shannon kyle at pobox.com
Fri Jan 3 11:54:16 EST 2014


On Fri, Jan 3, 2014 at 8:49 AM, Andre Joost <andre+joost at nurfuerspam.de> wrote:
> Am 03.01.2014 04:00, schrieb Kyle Shannon:
>> Is it okay to set a lat_1=lat_0,
>> and also specify lat_2.  I suspect it is, but I haven't found any
>> concrete definition on limits (and I don't really think there are,
>> within reason).
>> Thought I'd consult the pros on the list to be sure.
> In the formulas given by Snyder, a single parallel LCC projection is
> defined by lat_1=lat_2, but he makes no special treatment for lat_0 (the
> latitude of origin) is equivalent to lat_1 or lat_2 or not.

Right, I feel that lat_0 shouldn't really be considered in this logic.

> Reading older proj trac tickets, I gathered that lat_0=lat_1 is
> misinterpreted in proj4 as lcc single parallel projection. This does not
> coincide with the WKT projection strings supplied by ESRI and others.

Correct.  It may be a LCC 1SP, but it doesn't *have* to be.  It
depends on the presence of lat_2.

> Greetings,
> André Joost
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> Proj at lists.maptools.org
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My interpretation is that lat_1 must always be specified.  Whether or
not it is equal to lat_0 seems irrelevant.  If lat_1 == lat_2, then it
is a LCC 1SP.

BTW, are you referring to 'Map Projections: A Working Manual' or
another Snyder publication.



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