# [Proj] hammer parameters?

William Kyngesburye woklist at kyngchaos.com
Wed Jan 19 15:33:53 EST 2011

```On Jan 19, 2011, at 2:03 PM, strebe at aol.com wrote:

> I have been assuming that someone who knows something about proj would speak up. I don’t know anything about proj. However, Snyder’s formulation of Hammer includes a W parameter which controls the amount of bending in the parallels. The standard Hammar uses W = 1/2. Eckert-Greiffendorf uses W=1/4.
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W=0.5 makes sense, as this is the default GRASS uses, so that parameter is probably the same as in Snyder's.

> Perhaps M is the horizontal compression/vertical exaggeration.
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> To achieve Briesemeister under these assumptions, you would set W = 1/2, M = 0.93541 (or perhaps its reciprocal), and the projection center to 45°N.

I tried that already.  Still no good with W=0.5 and M=0.57142857 or M=1.75.

> So, again, though I know nothing about proj, I assume you will need “ob_tran”, which I infer to mean oblique transformation or somesuch.
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> — daan Strebe
> http://www.mapthematics.com
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> -----Original Message-----
> From: William Kyngesburye <woklist at kyngchaos.com>
> To: PROJ.4 and general Projections Discussions <proj at lists.maptools.org>
> Sent: Wed, Jan 19, 2011 11:47 am
> Subject: Re: [Proj] hammer parameters?
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> So, can anyone tell me what the M and W parameters mean, or at least what values
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> to use to get the Breisemeister (without using ob_tran)?
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> On Jan 13, 2011, at 11:01 AM, William Kyngesburye wrote:
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> > On Jan 12, 2011, at 5:33 PM, Frank Warmerdam wrote:
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> >> Folks,
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> >>
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> >> For what it is worth, it is possible to embed a literal PROJ.4 string
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> >> in GDAL/OGR WKT in which case that will be used as the translation to
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> >> PROJ.4 format.
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> >>
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> >> eg.
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> >> PROJCS["UTM Zone 11, Northern Hemisphere",
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> >>    GEOGCS["WGS 84",
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> >>        DATUM["WGS_1984",
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> >>            SPHEROID["WGS 84",6378137,298.257223563,
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> >>                AUTHORITY["EPSG","7030"]],
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> >>            TOWGS84[0,0,0,0,0,0,0],
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> >>            AUTHORITY["EPSG","6326"]],
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> >>        PRIMEM["Greenwich",0,
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> >>            AUTHORITY["EPSG","8901"]],
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> >>        UNIT["degree",0.0174532925199433,
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> >>            AUTHORITY["EPSG","9108"]],
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> >>        AUTHORITY["EPSG","4326"]],
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> >>    PROJECTION["Transverse_Mercator"],
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> >>    PARAMETER["latitude_of_origin",0],
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> >>    PARAMETER["central_meridian",-117],
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> >>    PARAMETER["scale_factor",0.9996],
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> >>    PARAMETER["false_easting",500000],
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> >>    PARAMETER["false_northing",0],
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> >>    UNIT["Meter",1],
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> >>    EXTENSION["PROJ4","+proj=utm +zone=11 +datum=WGS84 +wktext"]]
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> >>
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> >> When passing proj.4 strings to GDAL utilities which take
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> >> PROJ.4 as input you can include the +wktext option to force
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> >> literal inclusion of the PROJ.4 string.  For projections
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> >> completely not supported by GDAL you will need to create
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> >> WKT with some sort of fake projection (perhaps just use
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> >> the above and update the EXTENSION[] portion.
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> >>
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> > I tried this a few months ago for another unsupported projection in GDAL with
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> no luck.  Doesn't work here either.  Quote from Evan Rouault:
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> > "+wktext cannot help when OSR doesn't recognize the projection. It only helps
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> > to keep the extra options that OSR doesn't handle by itself."
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> > So, if GDAL doesn't support ob_tran, +wktext won't help.
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> > -----
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> > William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
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> http://www.kyngchaos.com/
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> >
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> > First Pogril: Why is life like sticking your head in a bucket filled with
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> hyena offal?
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> > Second Pogril: I don't know.  Why IS life like sticking your head in a bucket
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> filled with hyena offal?
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> > First Pogril: I don't know either.  Wretched, isn't it?
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> > -HitchHiker's Guide to the Galaxy
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> > _______________________________________________
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> > Proj mailing list
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> >
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> >
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>
> -----
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> William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
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> http://www.kyngchaos.com/
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> All generalizations are dangerous, even this one.
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-----
William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
http://www.kyngchaos.com/

"Mon Dieu! but they are all alike.  Cheating, murdering, lying, fighting, and all for things that the beasts of the jungle would not deign to possess - money to purchase the effeminate pleasures of weaklings.  And yet withal bound down by silly customs that make them slaves to their unhappy lot while firm in the belief that they be the lords of creation enjoying the only real pleasures of existence....

- the wisdom of Tarzan

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