[GRASS5] conversions and copyrights

[Roger Miller]

On Saturday 12 January 2002 10:01, Frank Warmerdam wrote:

>
>   o PROJ 4.4.5 already does datum shifting, integrated with the
> reprojection operation using the pj_transform() API.  You can use
> +datum=NAD27 and similar directives to enable datum conversion.
>
>   o PROJ 4.4.5 already has support integrated for Canadian NTv1 datum shift
>     files in addition to the US NADCON style data.
>
> Rather than re-invent some of this work based on the old proj code, I
> would much rather see it all accomplished in a more integrated way in
> GRASS 5.1 using PROJ 4.4.5, even if that code base is just adopted into
> the GRASS tree as is done now.  Though, given that we are moving to more
> modern use of shared libraries and so forth for 5.1 perhaps we could use
> PROJ.4 in it's more natural form.

Frank,

Thanks for the feedback.  I hadn't thought to look for newer versions of the 
proj library.  Certainly you are right that a more integrated approach is 
better.

Unfortunately I can't wait for 5.1.  I and many other people working in North 
America have to deal with the nad<->nad conversion on a nearly daily basis.  
I think the grass developers would be getting far more pressure to offer this 
capability if 5.0 had more North American users.  As it is, anyone using 
GRASS now in North America has to either ignore the conversion problems or 
cobble together some kind of work-around solution.

For those not aware, the nad27->nad83 conversion is not just a datum shift.  
There were errors in the nad27 datum that are corrected in the nad83 datum, 
and the conversion between the two data includes a datum shift plus some 
error corrections.  As a result, the nad27->nad83 conversion can't be 
completed with generalized datum shift formulas.

I think my first step will be to look into the newer version of the proj 
library.  From there I need to continue on my present course, because I want 
to have this capabiity in place on Monday.

My solution is probably not something that anyone wants for 5.1, but maybe it 
can be incorporated in 5.0 for the sake of the users in the US and southern 
Canada.

> I am prepared to assist substantially with such an effort.

I'm glad to hear that.  I looked briefly at the outline of GRASS's more 
general datum conversion capability in the programmer's manual.  That looks 
like more than I would want to tackle by myself.

> The license agreement you point of is not compatible with redistributing
> the grid shift data.  I assume this is the agreement for the NTv2 data.  Is
> that right?

That's right.  However, I had the impression that the document was actually a 
generic condition that they applied to most or all of their data.  There is a 
similar but separate document that covers software.

Roger Miller
Lee WIlson and Associates