[GRASS-user] DEM with bathymetric contour lines

[Markus Neteler]

On Mon, May 18, 2015 at 4:47 PM, Irantzu Alvarez <irantzu.alvarez at gmail.com>
wrote:
>
> I am trying to create a DEM from a bathymetric contour lines.

To replicate, I have downloaded a bathymetric DEM portion from
http://www.marine-geo.org/tools/maps_grids.php
(downloaded as GeoTIFF, LatLong, imported with r.in.gdal).

I am using GRASS GIS 7.0.svn here.

> Contours are
> in vector format and the elevation value is negative (integers).

ok, in my test case I have run

r.contour GMRTv2_7_bathy_mediterranean step=100 min=-4000 max=3500
output=GMRTv2_7_bathy_mediterranean_contours_100m

> To create
> the surface I have converted the contours in raster (v.to rast)

Yes:
v.to.rast input=GMRTv2_7_bathy_mediterranean_contours_100m
output=GMRTv2_7_bathy_mediterranean_contours_100m use=attr
attribute_column=level

> and then I
> have used r.surf.contour, but It doesn't work (there is no error but the
> resulting output raster is exactly the same as the previous one, without
any
> interpolation).

Strange. Here, with

r.surf.contour input=GMRTv2_7_bathy_mediterranean_contours_100m
output=GMRTv2_7_bathy_mediterranean_interpol

... I got back a nice bathymetric DEM (naturally, the "differences" map
generated with r.mapcalc shows some differences to the original map I
derived the contour lines from given the oversimplification done with the
vectorization).

> This are my region settings:
>
> g.region -p -a raster=contours at iiaa nsres=1 ewres=1
> projection: 1 (UTM)
> zone:       30
...
> rows:       27443
> cols:       114763
> cells:      3149441009

Which GRASS GIS version are you using?

> I need a DEM of very high resolution of a wide area. I am using a computer
> with large capacities for it.

Yes, but which operating system?

My full procedure below.

HTH,
Markus

-- 
http://consulting.neteler.org
http://courses.neteler.org/next-training/
http://gis.cri.fmach.it/neteler/


######## Test case procedure (GRASS GIS 7)
# import bathymetric map, downloaded from
http://www.marine-geo.org/tools/maps_grids.php
r.in.gdal /home/neteler/data/GMRTv2_7_20150525topo.tif
out=GMRTv2_7_bathy_mediterranean -o
g.region raster=GMRTv2_7_bathy_mediterranean
r.colors GMRTv2_7_bathy_mediterranean color=srtm_plus

# visualize imported map
d.mon wx0
d.rast GMRTv2_7_bathy_mediterranean

# generate contour lines (for our test case)
r.info GMRTv2_7_bathy_mediterranean
r.contour GMRTv2_7_bathy_mediterranean step=100 min=-4000 max=3500
output=GMRTv2_7_bathy_mediterranean_contours_100m
d.vect GMRTv2_7_bathy_mediterranean_contours_100m

# rasterize contour lines
v.to.rast input=GMRTv2_7_bathy_mediterranean_contours_100m
output=GMRTv2_7_bathy_mediterranean_contours_100m use=attr
attribute_column=level

# visualize colorized contour lines
d.mon wx1
r.colors GMRTv2_7_bathy_mediterranean_contours_100m color=srtm_plus
d.rast GMRTv2_7_bathy_mediterranean_contours_100m

# interpolate DEM from contour lines
r.surf.contour input=GMRTv2_7_bathy_mediterranean_contours_100m
output=GMRTv2_7_bathy_mediterranean_interpol
r.colors GMRTv2_7_bathy_mediterranean_interpol color=srtm_plus
r.info GMRTv2_7_bathy_mediterranean_interpol

# visualize new resulting map
d.mon wx2
d.rast GMRTv2_7_bathy_mediterranean_interpol

# generate differences map for validation
r.mapcalc "GMRTv2_7_bathy_mediterranean_diff = GMRTv2_7_bathy_mediterranean
- GMRTv2_7_bathy_mediterranean_interpol"
r.colors GMRTv2_7_bathy_mediterranean_diff color=differences

# visualize differences map
d.mon wx3
d.rast GMRTv2_7_bathy_mediterranean_diff

# optionally generate histogram or profiles via wxGUI
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