[Proj] hammer parameters?

[strebe at aol.com]

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.

Perhaps M is the horizontal compression/vertical exaggeration.

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. So, again, though I know nothing about proj, I assume you will need “ob_tran”, which I infer to mean oblique transformation or somesuch.

 

 — daan Strebe
http://www.mapthematics.com

 

 

-----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?


So, can anyone tell me what the M and W parameters mean, or at least what values 

to use to get the Breisemeister (without using ob_tran)?



On Jan 13, 2011, at 11:01 AM, William Kyngesburye wrote:



> On Jan 12, 2011, at 5:33 PM, Frank Warmerdam wrote:

> 

>> Folks,

>> 

>> For what it is worth, it is possible to embed a literal PROJ.4 string

>> in GDAL/OGR WKT in which case that will be used as the translation to

>> PROJ.4 format.

>> 

>> eg.

>> PROJCS["UTM Zone 11, Northern Hemisphere",

>>    GEOGCS["WGS 84",

>>        DATUM["WGS_1984",

>>            SPHEROID["WGS 84",6378137,298.257223563,

>>                AUTHORITY["EPSG","7030"]],

>>            TOWGS84[0,0,0,0,0,0,0],

>>            AUTHORITY["EPSG","6326"]],

>>        PRIMEM["Greenwich",0,

>>            AUTHORITY["EPSG","8901"]],

>>        UNIT["degree",0.0174532925199433,

>>            AUTHORITY["EPSG","9108"]],

>>        AUTHORITY["EPSG","4326"]],

>>    PROJECTION["Transverse_Mercator"],

>>    PARAMETER["latitude_of_origin",0],

>>    PARAMETER["central_meridian",-117],

>>    PARAMETER["scale_factor",0.9996],

>>    PARAMETER["false_easting",500000],

>>    PARAMETER["false_northing",0],

>>    UNIT["Meter",1],

>>    EXTENSION["PROJ4","+proj=utm +zone=11 +datum=WGS84 +wktext"]]

>> 

>> When passing proj.4 strings to GDAL utilities which take

>> PROJ.4 as input you can include the +wktext option to force

>> literal inclusion of the PROJ.4 string.  For projections

>> completely not supported by GDAL you will need to create

>> WKT with some sort of fake projection (perhaps just use

>> the above and update the EXTENSION[] portion.

>> 

> I tried this a few months ago for another unsupported projection in GDAL with 

no luck.  Doesn't work here either.  Quote from Evan Rouault:

> 

> "+wktext cannot help when OSR doesn't recognize the projection. It only helps 

> to keep the extra options that OSR doesn't handle by itself."

> 

> So, if GDAL doesn't support ob_tran, +wktext won't help.

> 

> -----

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

> http://www.kyngchaos.com/

> 

> First Pogril: Why is life like sticking your head in a bucket filled with 

hyena offal?

> Second Pogril: I don't know.  Why IS life like sticking your head in a bucket 

filled with hyena offal?

> First Pogril: I don't know either.  Wretched, isn't it?

> 

> -HitchHiker's Guide to the Galaxy

> 

> 

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-----

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

http://www.kyngchaos.com/



All generalizations are dangerous, even this one.





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