[Proj] GeoTiff <-> Proj.4

[Gerald I. Evenden]

On Wednesday 01 October 2008 10:08:12 am support.mn at elisanet.fi wrote:
> Hello,
>
> There is no general rule how to map GeoTiff GeoKeys to proj.4
> parameters (or is there?) Every projection has it's own mapping?
>
> Can I write "lat_ts" instead of "lat_0" ??

lat_ts denotes latitude of true scale while lat_0 generally refers to latitude 
of origin.  One should *never* assume that they create the same value.

> Is there "lon_ts"?

I have never used it. "Longitude of true scale" is a meaningless term.

> Here I have those keys I have found some mapping,
> but how about the others. Must be different for each
> projection?
>
> ----------
>
> ProjLinearUnitSizeGeoKey	3077 in meters
>
> ProjStdParallelGeoKey		3078 in GeogAngularUnit -> lat_1
> ProjStdParallel2GeoKey	3079 in GeogAngularUnit -> lat_2
> ProjOriginLongGeoKey		3080 in GeogAngularUnit  -> lon_0
> ProjOriginLatGeoKey		3081 in GeogAngularUnit  -> lat_0
> ProjFalseOriginLongGeoKey	3084 in GeogAngularUnit
> ProjFalseOriginLatGeoKey	3085 in GeogAngularUnit
> ProjCenterLongGeoKey	3088 in GeogAngularUnit
> ProjCenterLatGeoKey		3089 in GeogAngularUnit
>
> ProjFalseEastingGeoKey	3082 in ProjLinearUnits -> x_0
> ProjFalseNorthingGeoKey	3083 in ProjLinearUnits -> y_0
> ProjFalseOriginEastingGeoKey	3086 in ProjLinearUnits
> ProjFalseOriginNorthingGeoKey	3087 in ProjLinearUnits
> ProjCenterEastingGeoKey	3090 in ProjLinearUnits
> ProjCenterNorthingGeoKey	3091 in ProjLinearUnits
>
> ProjScaleAtOriginGeoKey	3092 in ratio   -> k_0
> ProjScaleAtCenterGeoKey	3093 in ratio
>
> ProjAzimuthAngleGeoKey	3094 in GeogAzimuthUnit -> alpha
> ProjStraightVertPoleLongGeoKey	3095 in GeogAngularUnit
> ProjRectifiedGridAngleGeoKey	3096 in GeogAngularUnit

What a mish-mash of terminology.  That is why I believe that the equations for 
the projection should be mandated as part of any projection description 
because they resolve the usage and meaning of control contants.

And I suspect that the above often have different "flavors" of description in 
French, German, Italian, Russian, Chinese, etc..  Again, the mathematical 
description is the only lingua franca of the definition.

-- 
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist