[Proj] GeoTiff <-> Proj.4
Gerald I. Evenden
geraldi.evenden at gmail.com
Wed Oct 1 11:40:06 EDT 2008
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
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