[Proj] GeoTiff <-> Proj.4

Gerald I. Evenden geraldi.evenden at gmail.com
Thu Oct 2 14:15:50 EDT 2008

On Thursday 02 October 2008 9:14:13 am support.mn at elisanet.fi wrote:
> Frank Warmerdam <warmerdam at pobox.com> kirjoitti:
> > The page at:
> >
> >   http://geotiff.maptools.org/proj_list/


Sorry about the truncated earlier reply to this email as I was interupted by 
the phone and accidentally hit "send."

Sorry but the terminology of Mercator(1sp)---(2sp) freaks me out.  And the 
need for two entries.

> Geotiff number 15, "stere" uses "lat_0=CenterLat", not
> mentioned? Or is it only intergraph?

That usage of lat_0 was mentioned before.

> Geotiff number 27, "tmerc" soth oriented can not be used
> directly, unless you turn all signs somewhere using extra
>  "ifs"? Isn't that forbidden, to have a south orientated map?
> How the people know where the north is if that is upside
> down?

I spent two weeks in Australia almost 40 years ago and don't remember everyone 
standing on their heads.  Unfortunately, I do not remember seeing a map at 
the time so do not know if they plot them upside down.  ;-)  But I had a good 
time and even managed to survive driving on the wrong side.

At the moment, the only place a south option is used is for UTM where a false 
northing of 10,000,000 meters is added when the +south option is spec'd. The 
issue of a 180 rotated Cartesian system for southern hemisphere usage has 
only come up recently and I am not sure how widespread this usage is nor, 
since a minus scale handles the problem, whether an added option is truly 
needed.  Also is this upside down coordinates system part of a grid system?  
Are the maps printed with south up?

> And Intergraph is using mostly different fields instead of
> those given in your link?
> ---------
> Linear names are easy: whatever given ->x_0 and y_0
> Ratio names also easy: whatever given -> k_0

Is the term "ratio" proper.  I simply look at it as a unitless multiplier.

> Angular names are most difficult and all are not using same
> names? There is no general rule? Ok. I make a mapping
> table for the names then.
> ----------
> BTW: There is couble of typos. Lcc(1) and Lcc(2) are entered
> both as number 9. I am assuming that Lcc(2) is number 8 and
> Lcc(1) is number 9?

I would like to add: where did this Laborde Oblique Mercator come from?  Are 
there any spec for it?  From Mugnier, it is basically the same operations in 
the general case as previously discussed in the special case of 
Gauss-Schreiber (Laborde) projection.  From the above web site entry for
Laborde Oblique Mercator:

EPSG Notes
 Can be accomodated by Oblique Mercator method (code 9815).

9815 make the statement: 
 The formula is exactly the same as for Hotine Oblique Mercator. I consider 
this to be an alias for that projection. See it for details on formula.


The problem is that this erroneous position is pandemic with Transverse 

This issue of Swiss "oblique mercator" is the most universally screwed up 
problem.  The only site I have seen that seems to have a handle on it is the 
Swiss and as they portray it is simply a Mercator rotated such that the axis 
of the pole of the projection is in the merdianal plane of the projection and 
that the equator of the projection passes through the central parallel.  And 
it uses the Gauss conformal transformation to a sphere as an intermediate 
step.  *THUS* it is *NOT* a Hotine projection.  Somewhere, someone came along 
and also established a Hotine projection for Swiss imaging applications.  
WHY?  Probably because they did not have a clue as to the original Swiss 
projection and then just assumed that because "oblique" was in its name it 
must be Hotine.


Yes, I am yelling.

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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