[Proj] How grids work in PROJ4

J. Luis jmfluis at gmail.com
Sun Jan 15 15:12:07 EST 2012

On 15-01-2012 13:58, Thomas Knudsen wrote:
> 2012/1/14 Michal Seidl <michal.seidl at gmail.com 
> <mailto:michal.seidl at gmail.com>>
>     - Mikael Rittri explanation helps me a lot, I was really for a moment
>     confused by Frank's one
> Mikael's clarification was, indeed, excellent and useful
>     - Joaquim formula h = H-N is OK. But as Frank said +geoidgrids is only
>     name and can be used for other height correction which is exactly my
>     situation.
> But please note that Wikipedia and leading geodetic textbooks 
> (Hoffmann-Wellenhof & Moritz: Physical Geodesy, as well as Torge: 
> Geodesy) use a different notation:
> h: height above ellipsoid
> H: orthometric height (which to an excellent approximation is 
> equivalent to the height above the geoid)
> Hence: h = N + H
> So following Joaquim's suggestion of +H and +h options is quite risky. 
> Out of context you can never be sure what is meant by H and h.
> /Thomas

Ai, this is embarrassing for me. Off course I mistakenly swapped the H/h 
as it never crossed my mind going against the notation followed by the 
"Physical Geodesy" bibles.

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