[GRASSLIST:4151] Re: adding a field from raster image to existing site data

Thomas Dewez thomas.dewez at brunel.ac.uk
Thu Jul 25 11:51:18 EDT 2002


----- Original Message -----
From: "Markus Neteler" <neteler at itc.it>
To: "Thomas Dewez" <thomas.dewez at brunel.ac.uk>
Sent: Thursday, July 25, 2002 4:36 PM
Subject: Re: [GRASSLIST:4019] adding a field from raster image to existing
site data


> On Thu, Jul 04, 2002 at 11:42:07AM +0100, Thomas Dewez wrote:
> > Dear all,
> >
> > My project is moving on thanks to your help. The next question I'd have
is
> > to interpolate a DEM for which I have these information:
> > 1. irregularly spaced Z stored in an raster map (2.5 million data
points!)
> > 2. corresponding precision for Z posts in a second raster image.
> >
> > Are site coverages the only sources that I can feed to s.surf.rst or can
I
> > interpolate a spline with tension directly from a raster map? By the
way,
> > are sites map plain ASCII files?
> >
> > If site coverage is the only solution, then how can I combine both
raster
> > map inside a single site map? I want to use the precision image as the
> > "smoothing attribute" of the interpolation. So how do I make the
precision
> > raster map become attribute 2 of the sites?
> >
> > Finally, s.surf.rst is extremely CPU intensive. What are the "cooking
> > tricks" to use to speed up/avoid slowing down the process?
>
> which version do you use? s.surf.rst is 2600% faster since
> GRASS 5.0.0pre4

2600% is a hell of a lot faster. I am still using GRASS5 pre3. So far the
computation was taking between 7 and 12 hours. I'll install pre5 right away.

Do you know if there is/was a limitation on the number of rows and columns
built in the code in GRASS5-pre3? I noticed, when the computer was not
crashing :-(, that the output DEM was always 1800 columns wide by
1300-something high. That was not the size of the final DEM I was expecting.

The way it was computing was also somewhat bizarre.The result always
computed the upper right corner of the whole extent. The algorithm seemed to
work backwards from the NE towards the SW. Is this a correct interpretation?
How bizarre...

Thanks so much for letting me know this little tip

Thomas
>
> just to let you know.
>
>  Markus
>



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