[GRASS-dev] Re: [GRASS GIS] #163: g.transform no longer calculating error for 2nd order transformation

[Michael Barton]

I don't remember reopening it, but don't think it was ever "fixed".  
There was some discussion about whether this is a "bug" or not. As I  
remember it, here is what happens. If you select 6 points for a 2nd  
order transform, you get 00's or bogus numbers for the RMA  
calculations. I think someone pointed out that because 6 is a minimum  
number, you should get 0's. This seems weird and not too useful. Also,  
at least a couple of people in my lab ended up with blank maps with  
exactly 6 points. If you use 7 or more points, all problems go away.

I took this to mean that what the docs *really* mean is that you must  
have *more* than 6 points for a 2nd order transformation. I changed  
the GUI accordingly and suggested that the docs be changed. Others  
have said that, no, you need *at least* 6 points, not more than 6  
points.

I have not retested this, but AFAIK, there was no change to g.transform.

Michael
______________________________
C. Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University
Tempe, AZ  85287-2402
USA

voice: 480-965-6262; fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

On Jan 16, 2009, at 3:29 PM, GRASS GIS wrote:

> #163: g.transform no longer calculating error for 2nd order  
> transformation
> ----------------------- 
> +----------------------------------------------------
>  Reporter:  cmbarton  |       Owner:  grass-dev at lists.osgeo.org
>      Type:  defect    |      Status:  reopened
>  Priority:  major     |   Milestone:  6.4.0
> Component:  default   |     Version:  svn-develbranch6
> Resolution:            |    Keywords:  g.transform georectify
>  Platform:  All       |         Cpu:  Unspecified
> ----------------------- 
> +----------------------------------------------------
> Comment (by martinl):
>
> Any reason why this ticket is still open?
>
> -- 
> Ticket URL: <http://trac.osgeo.org/grass/ticket/163#comment:10>
> GRASS GIS <http://grass.osgeo.org>