[Proj] Cassini coordinate reprojection problem

Chris Faulkner christopher.faulkner at ntlworld.com
Sat Mar 19 09:17:20 EST 2005

Sorry for the delay in response. I am doing this in the evenings -
unfortunately, it doesn't form part of my day job !

Following your suggestions, I split up the conversion and compared what
was happening on each side - to and from lat/long. I found that the
conversion of Cassini to Geographics  was the same as in GEOTRANS. AT
that point it became even more obvious that it was my mistake - no way
has proj4 got a bug in TM ! I then realised I had left off the scale
factor which on the British National Grid is 0.9996. This made all the
difference. I was surprised just how much this moves the coordinates. 

Thanks for all your help on this and thanks for the follow up now. I
never cease to be amazed at the level of community support there is out
there for this type of project.


> -----Original Message-----
> From: proj-bounces at xserve.flids.com 
> [mailto:proj-bounces at xserve.flids.com] On Behalf Of Gerald Evenden
> Sent: 18 March 2005 18:50
> To: PROJ.4 and general Projections Discussions
> Subject: Re: [Proj] Cassini coordinate reprojection problem
> I have not heard anything more about the Cassini problems.  Have they 
> been
> resolved?  I do not like to leave an issue on the table unresolved.
> Thank-you.
> There will be a minor change to Cassini in the next release 
> which only 
> affects
> the longitude returned during inverse where the footprint latitude is 
> 90°.  Currently
> lproj (and presumably proj) returns an odd value.  In the 
> future, lon_0 
> will be
> returned.  Longitude in this situation is meaningless anyway. 
> _____________________________________
> Jerry and the low riders: Daisy Mae and Joshua.
> "The whole religious complexion of the modern world is due to 
> the absence from Jerusalem of a lunatic asylum." Havelock Ellis, 1914
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