[mapserver-users] Re: EPSG:42304 -> EPSG:3978? or 3979?

[Frank Warmerdam]

On 11-06-29 05:54 PM, myOpenLayersUName wrote:
> Oh Jeff,
>
> It seems I'm always saying "no" to that question from you and then finding
> out later that I should have said "yes" but didn't realize it. So, first of
> all, thank you for continuing to respond to my questions even when I'm
> repeatedly too slow to follow something that's readily apparent to others.
>
> Unfortunately, in answer to your question this time, I'm going to go with
> "sort of."  You have confirmed my understanding of what happened, but I'm
> still not sure which of these two new EPSG codes I should be picking to
> update my own application and get away from using 42304.
>
> Can I just change the EPSG code to one or the other of the new ones (or
> either, since they seem to be the same as far as I can tell)? Or, do I have
> to reproject the data from the old 42304 to one of them before I can do
> this? When I compare the PROJ4 definitions of the new and old, they aren't
> the same and that suggests I need to reproject but someone told me that I
> should not have to do that... that I should be able to just change the code
> in my Mapfiles and OpenLayers WMS definitions.

Joanne,

The difference between 3978 and 3979 is that 3978 is NAD83 while
3979 is NAD83 (Canadian Spatial Reference System).  I don't know much
about CSRS but I assume it is a refined NAD83 - roughly similar to
HPGN in the USA.  Most software in the free software world won't do
anything special with NAD83 (CSRS) and will not likely even know enough
to treat it as NAD83.  So my suggestion is to stick with 3978 unless
you really really know you want to label the data as NAD83 (CSRS) and
are willing to suffer incompatibilities due to it.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent