[Proj] Potentially (theoretically) dangerous changes in Proj4 internal routines that affect the end results..

Charles Karney charles.karney at sri.com
Sun Nov 8 18:36:45 EST 2015

Dear Janne,

I'm against given the new utm implementation a different name.  The
whole point is that a naive user can request "utm" and get the best
available implementation of the projection.

Conceivably, the old version could be made available as "oldutm" or
whatever.  But I would like to see some evidence this is really needed
given that with the standard UTM conventions for zones, we are only
talking about a ~ 0.1mm difference -- and this is also the round-trip
discrepancy in the old implementation.


On 11/08/2015 06:12 PM, support at mnspoint.com wrote:
> Hello,
> why not just add a new projection called "utm2" or "newutm" or "xutm" ..
> and use it like "proj=utm2" etc. I would like more if the new utm was
> called different so that the old references would stay where they always
> been.. just to stay consistent..
> Regards Janne.
> --------------------------------------------------------
> Thomas Knudsen kirjoitti 02.11.2015 14:15:
>> If memory serves me right, you should use something like +proj=tmerc
>> +x_0=500000 +lon_0=...   +scale=0.9996 to invoke the Snyder algorithm
>> (fully analogous to what you had to do up until now to get utm using
>> +proj=etmerc)
>> /thomas

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