[GRASS-user] Draping map

[Tom van der Putte]

Indeed, you can smooth things out in multiple ways for visualization
purposes, but interpolating the data from 90, to 1 m resolution is not the
best way to go when you want to do important analyses.

Good luck,
Tom

-----Original Message-----
From: grass-user-bounces at lists.osgeo.org
[mailto:grass-user-bounces at lists.osgeo.org] On Behalf Of Tom Russo
Sent: dinsdag 20 januari 2009 17:11
To: grass-user at lists.osgeo.org
Subject: Re: [GRASS-user] Draping map

On Tue, Jan 20, 2009 at 03:31:33PM +0100, we recorded a bogon-computron
collision of the <edmondo.elisei at gmail.com> flavor, containing:
> Dear Tom,
> thanks for your clear explanation.
> 
> I think I should obtain better results by this procedure:
> 1) Building vector contours from dem 90 meters;
> 2) Conversion contours to raster
> 3) Running r.surf.rst in order to generate a new dem with higher
resolution

If you're only interested in improving the view in NVIZ, you might try
instead
using bilinear interpolation of your DEM to higher resolution.  The
resulting
DEM won't be a good one to use for serious analytical work (or so I
understand)
but will be smoother than the stair-step view you'll have merely by
resampling.

Check out r.resamp.interp.  Set your region to the resolution of the TIFF
you
plan to use as the color map, and use r.resamp.interp on the DEM with the
bilinear interpolation option.

I use this technique often for draping 2m-per-pixel USGS topo quad maps over
the corresponding 10m-per-pixel DEMs when teaching topo map reading skills
to
search and rescue volunteers.  For visualization purposes, it is adequate
and
produces pretty pictures without stairsteps.  For other purposes it is
probably
quite poor as I understand there are significant artifacts that can creep
in.

> 2009/1/20, Tom van der Putte <tom at vdputte.nl>:
> >
> >  Hi Edmondo,
> >
> > If I get your question correctly:
> >
> > Resampling data with a spatial resolution of 90m might increase the
> > resolution of the DEM itself , but it will not increase the detail of
the
> > data, only the number of pixels in your DEM. For instance, when you
> > downscale an image of 1 x 1 pixel by a factor 2 (both in x and y
direction),
> > the new image will consist of four pixels (2x2). Which all have the same
> > value as the original 1 pixel. So although the number of pixels has been
> > increased, the detail remains the same.
> >
> > *From:* grass-user-bounces at lists.osgeo.org [mailto:
> > grass-user-bounces at lists.osgeo.org] *On Behalf Of *Edmondo Elisei
> > *Sent:* dinsdag 20 januari 2009 9:50
> > *To:* GRASS user list
> > *Subject:* [GRASS-user] Draping map
> >
> >
> >
> > Hi,
> > I've a DEM with 90m resolution and a tif map (1 m res).
> >
> > In draping the tif on my dem the resultant map in nviz has a very low
> > quality.
> > I tried changing the resolution of the DEM (r.resamp) in order to have
the
> > same than tif, but I didn't obtain improvements.


-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236
http://kevan.org/brain.cgi?DDTNM
  In some cultures what I do would be considered normal. 
                                  -- Ineffective daily affirmation 

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