[Proj] NAD27 and WGS84 woes

Michal Migurski mike at stamen.com
Sat Nov 22 14:13:51 EST 2008

>> I get (565373.10, 4184212.50).  This is still pretty far off what you
>> were expecting, so I wonder if your expectations are wrong.  Or  
>> perhaps 30
>> meters the best you can accomplish with the data precision you have?
> Frustrating, I don't know. I'm reading the FAQ's on datum shift  
> files - FWIW, I'm using PROJ on a debian server where I've simply  
> installed it all via Apt. I didn't build/install myself. Does the  
> fact that my explicitly-given +towgs84 arguments have no effect mean  
> anything here? Wouldn't those be replacements for missing grid shift  
> files?

A quick followup on where I've gotten to.

I downloaded the PROJ.4 source and datum shift grids, and moved all  
the datum files into nad/ in the source directory. I configured and  
built proj like this:

	./configure --prefix=/tmp/proj
	make install

...then moved just the conus file and ditched the remainder of the  

	cp -v /tmp/proj/share/proj/conus /usr/share/proj/

Now I'm getting results that are closer to what I would expect. Thank  
you again for pointing this out.

Isn't it the case that without the datum shift files, proj outputs the  
wrong numbers? Why wouldn't these be included in the default build and  
debian package along with everything else?


michal migurski- mike at stamen.com

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