[Proj] proj=undef ??

[Mikael Rittri]

Janne, you wrote:

> simply since you don't need any projection to do datum calculations.

Do you mean that datum shifts can be done in longlat? True, but it 
was you who said that the coordinates were not in longlat but in 
some "undef" projection.  I though "undef" meant that you had no 
idea of how those coordinates are related to longlat.  

Let't take a concrete example:

proj=undef
ellps=bessel
towgs84=123,456,789
no_defs 

Now, I say that the input point is 

53479811	97344703

Can you tell me how this point could possibly be translated to 

proj=undef
datum=WGS84

Or maybe you can tell me under what circumstances you want to 
use such a feature?

-- Mikael 

-----Original Message-----
From: proj-bounces at lists.maptools.org [mailto:proj-bounces at lists.maptools.org] On Behalf Of support.mn at elisanet.fi
Sent: den 21 juni 2011 20:43
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] proj=undef ??

Mikael,

simply since you don't need any prjection to do datum calculations.

Janne.

----------------------------

Mikael Rittri [Mikael.Rittri at carmenta.com] kirjoitti: 
> Hello Janne,
> if I understand you right, what you want is impossible.  
> 
> If the projection is unknown, any input coordinates will be 
> non-georeferenced. So, how could the datum shift machinery do anything 
> on coordinates that cannot be interpreted?
> 
> Maybe I misunderstand what you want to do.
> 
> Mikael Rittri
> Carmenta
> Sweden
> http://www.carmenta.com
> 
> -----Original Message-----
> From: proj-bounces at lists.maptools.org 
> [mailto:proj-bounces at lists.maptools.org] On Behalf Of 
> support.mn at elisanet.fi
> Sent: den 19 juni 2011 12:30
> To: proj at lists.maptools.org
> Subject: [Proj] proj=undef ??
> 
> Hello,
> 
> there is a need to have an undefined projection with possible datum shift like:
> 
> proj=undef
> ellps=bessel
> towgs84=.....
> no_defs
> 
> That would then transfer the projection input to output without doing any forward or inverse calculations even if those routines called but allowing datum shifting.
> 
> So the absolutely minimal definition would be
> 
> proj=undef
> datum=undef
> 
> or shorter version
> 
> proj=undef
> 
> and that would feed all input directly to the output. Those switches would allow the end user to control the handling of the data.
> 
> So the "proj=undef" is same as not doing anything by the projection library if called but not giving any error messages about missing projection but doing all datum shifting if requested. Any ideas?
> 
> Regards: Janne.
> 
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