[R-sig-Geo] How to interpolate river cross section with R?

[ivan marchesini]

Hi,
in the past, for a similar problem, I used GRASS and in particular the
module r.surf.nnbathy which is an addon of GRASS.
I used this module to perform a delaunay triangulation considering both
the cross section points and the grid points (only those outside of the
river width). Obviously this approach can work only if the cross section
data are not really sparse respect to the DEM resolution. But since you
have 500 m interval cross section I think this could be a problem.

Another way is to pass, unfortunately, from the proprietary software
HEC-RAS. You can (1)import your cross section data (2)use the
"interpolate cross-section" function and then (3)export (non so simple)
all the cross sections (original and interpolated) as x,y,z values.
At this point you can go back and at GRASS and r.surf.nnbathy. 

The only problem is that the result is a sharp rigid surface, but you
can try to smooth it, for example, using some kernel filter.

hope this help.

ivan


Il giorno sab, 10/12/2011 alle 13.43 -0600, Stephen Sefick ha scritto:
> I think I would look into GRASS GIS.  There are some very good 
> interpolation algorithms that are implemented there already.  Likely, 
> you can do this with either R or GRASS, whether it is sensible is up to 
> you.
> 
> It sounds like the survey data and the DEM data are referenced to 
> different elevation datums.  How far off are the elevation values?
> 
> On Sat 10 Dec 2011 08:24:38 AM CST, Wongwatana Sombunying wrote:
> > Dear all
> >
> >            I have two data elevation sources which are DEM grid file and
> > river cross-section surveyed data. DEM data is grid file covering the whole
> > watershed area. Surveying data is 500-m interval cross sections along a
> > river reach in the watershed area. However, these are much difference in
> > elevation value at the same coordinate points. I want to generate a new
> > grid file from surveyed data along the river reach to be input of
> > hydrodynamic model.  Can I solve this problem with any R packages?  or  Can
> > I use R to  interpolate river cross section between upstream and downstream
> > river cross sections?
> >
> > The example of 2 cross section data are as following :
> >
> > Cross section No- 1
> > chainage,x,y,z
> > 0,537545.1,2219340,452.11
> > 4,537541.1,2219340,452.05
> > 12,537533.2,2219339,451.54
> > 14,537531.2,2219338,451.6
> > 16,537529.2,2219338,451.39
> > 24,537521.3,2219337,450.13
> > 34,537511.4,2219336,450.32
> > 39,537506.5,2219335,448.55
> > 44,537501.5,2219334,447.05
> > 49,537496.6,2219333,446.15
> > 54,537491.6,2219333,445.58
> > 59,537486.7,2219332,445.11
> > 64,537481.7,2219331,445
> > 69,537476.8,2219331,444.83
> > 74,537471.8,2219330,444.94
> > 79,537466.9,2219329,444.69
> > 84,537461.9,2219329,444.76
> > 89,537456.9,2219328,444.8
> > 94,537452,2219327,444.94
> > 99,537447,2219326,445.04
> > 104,537442.1,2219326,445.94
> > 110,537436.2,2219325,446.89
> > 114,537432.2,2219324,450.51
> > 124,537422.3,2219323,457.19
> > 134,537412.4,2219322,464.5
> > 144,537402.5,2219320,471.79
> > 154,537392.6,2219319,478.5
> >
> > Cross section No- 2
> >
> > chainage,x,y,z
> > 0,537545.1,2219340,452.11
> > 4,537541.1,2219340,452.05
> > 12,537533.2,2219339,451.54
> > 14,537531.2,2219338,451.6
> > 16,537529.2,2219338,451.39
> > 24,537521.3,2219337,450.13
> > 34,537511.4,2219336,450.32
> > 39,537506.5,2219335,448.55
> > 44,537501.5,2219334,447.05
> > 49,537496.6,2219333,446.15
> > 54,537491.6,2219333,445.58
> > 59,537486.7,2219332,445.11
> > 64,537481.7,2219331,445
> > 69,537476.8,2219331,444.83
> > 74,537471.8,2219330,444.94
> > 79,537466.9,2219329,444.69
> > 84,537461.9,2219329,444.76
> > 89,537456.9,2219328,444.8
> > 94,537452,2219327,444.94
> > 99,537447,2219326,445.04
> > 104,537442.1,2219326,445.94
> > 110,537436.2,2219325,446.89
> > 114,537432.2,2219324,450.51
> > 124,537422.3,2219323,457.19
> > 134,537412.4,2219322,464.5
> > 144,537402.5,2219320,471.79
> > 154,537392.6,2219319,478.5
> >
> >      Thank you for your help.
> >
> 

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Ivan Marchesini
Perugia (Italy)
Socio fondatore GFOSS "Geospatial Free and Open Source Software" http://www.gfoss.it
e-mail: ivan.marchesini at irpi.cnr.it
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