[Proj] proj deployment question

[jjholt at hiwaay.net]

Thanks for the response, I think I understand the issues now. I always specify
an ellipse in the init string, so it sounds like I'm OK!

Jeff


Quoting Frank Warmerdam <warmerdam at pobox.com>:

> jjholt at hiwaay.net wrote:
> > I have created a VC++ COM component that our application uses for
> projection
> > services. It links with proj as a static Win32 library to do the
> actual projection.
> > 
> > It works great, but I'm wondering about deployment issues. Normally I
> thought
> > the proj library requires some files - eg "nad" directory and maybe
> others.
> > However my component seems to work even on systems without any other
> proj files
> > on it.
> > 
> > We only do relatively simple stuff - geographics to/from UTM,
> geographic to from
> > Mercator, and UTM zone to zone. Is that why? Maybe "nad" is only
> needed for
> > "datum shifts"? I don't know what a "datum" is, let alone how to shift
> one :-)
> > 
> > I suppose another way to put it is: what capabilities won't work
> without
> > external proj files?
> 
> Jeff,
> 
> Without the contents of the nad directory you won't be able to use the
> init files (eg. +init=epsg:4326) or do grid shift based datum shifts
> (ie. NAD27 -> NAD83).  Also the default values found in proj_def.dat
> won't
> be in play - so you may need to be explicit about things like ellipsoid
> for instance.
> 
> If you are careful to fully define your coordinate systems, the only
> real
> capability you should be missing is the grid shift datum shifting. 
> Note
> that +towgs84 datum shifting will still work.
> 
> PS. There is a modest COM component now found in proj/com.
> 
> Best regards,
> -- 
> ---------------------------------------+--------------------------------------
> 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    | President OSGeo,
> http://osgeo.org
> 
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