[GRASSLIST:1910] Re: i.ortho.photo on osx

Richard Greenwood Rich at GreenwoodMap.com
Fri Nov 28 19:59:43 EST 2003

At 10:07 AM 11/26/2003, Markus Neteler wrote:

>Above problems should be fixed now (in 5.3-CVS). Reason was
>that a DEM of FCELL type was not read properly.
>In case of such troubles either update i.ortho.photo or use
>'r.recode' to make the DEM of DCELL type.

Markus, Ian;

I revisited my problematic project, converted to DCELL and it worked very 
nicely. Thanks Markus! But, I am confused on FCELL versus DCELL. I assumed 
that my metric DEM was integers and that converting to feet created a 
floating point, or double precision DEM, thus avoiding the problem you 
describe above. But what is the difference between FCELL and DCELL?

An important note (especially for Ian), my Overall rms error was 17.92 with 
my DEM in feet, but went down to 1.71 with a DCELL DEM in meters. I believe 
this is because the vertical units must be the same as the horizontal 
units. In other words, by converting to feet I was able to bypass the 
problem Markus has described and create a visually acceptable ortho 
rectification, but not a 'correct' rectification. I had attributed the high 
rms error to bad data, but I no longer believe that to be the case.

Two 'off topic' notes:

Markus - I have a 5.0.3 cygwin binary distribution at 
www.greenwoodmap.com/grasss (see configure.log for configure options) I 
have been using it for about two weeks and I am reasonably confident with 
it. In my limited testing, PostgreSQL seems to be working, too!

Ian - my sister and here ex-husband (Helen and Paul Hansma) both 
teach/research at UCSB in surface biology and physics. Please give them my 
regards if you happen to know them.

Best regards,

Richard W. Greenwood, PLS
Greenwood Mapping, Inc.
Rich <at> GreenwoodMap <dot> com
(307) 733-0203

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