[Proj] hammer parameters?

William Kyngesburye woklist at kyngchaos.com
Wed Jan 12 15:59:24 EST 2011

On Jan 12, 2011, at 1:28 PM, OvV_HN wrote:

> In reply to:
> From: William Kyngesburye <woklist <at> kyngchaos.com>
> Subject: hammer parameters?
> Date: 2011-01-11 16:44:43 GMT
> Reply:
> libproj4: A Comprehensive Library of Cartographic Projection Functions 
> (Preliminary Draft)
> Gerald I. Evenden
> November 22, 2008
> pag 132: Table 9.2: Oblique projections using +ob_tran
> http://home.comcast.net/~gevenden56/proj/index.html

OK, the ob_tran thing seems to work in proj4, though it doesn't really explain the M and W parameters, and I don't see what that M=0.9354143 value has to do with the 1.75 ratio of the Breisemeister, or why the hammer projection is not used directly.

But, GDAL rejects ob_tran, so I can't really do anything useful with it.  I can't use GRASS to project a raster because hammer appears to not have an inverse (I saw a patch posted to the list last December, but code didn't appear to correctly match the formulas on the mentioned page), and I don't know if GRASS supports ob_tran either.

William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>

"This is a question about the past, is it? ... How can I tell that the past isn't a fiction designed to account for the discrepancy between my immediate physical sensations and my state of mind?"

- The Ruler of the Universe

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