Fwd: [GRASS-user] Creation of a DEM

[Edward Tomlinson]

Hi,

I am also trying to create a DEM from a shapefile.

Once again i have some questions about the cell resolution and the
interpolation.

The use of this is for precision agriculture.

The shapefile was generated from a 2cm accuracy RTK GPS. Height variation is
about 1 metre (over 1200metres). The shapefile isn't exactly what you would
call a contour map. The resulting shapefile is made up of rectangles of
equal height. Each rectangle is 8m wide (always as this is the swath width
used). The length varies as it keeps ~equal heights together. Technically i
suppose this is a contour map, however equal height rectangles are not
connected and are not part of the same shape...

My other problem is trying to work out what gradient splits should be used.
As in i beleive i should use the standard deviation of height as the
gradient step value. Does this sound correct??

Also i need to restrict the boudary of the DEM to another shapefile. It is
just a single shape of the boundary of the field. Mostly all the data is
there, however some interpolation will be needed.


Currently i am having trouble reading the file in using v.in.ogr.
command:
v.in.ogr 'dsn=shapefile name' output=elevation09 'layer=Elevation Map 9'
Result:
GRASS_INFO_WARNING Area size 9e..., area not imported
....
0 areas imported

THere are many columns in the .df file. How can i only import the ones i
want? Clearly i have missed something.

Any help would be greatly appreciated.

THanks,
Ed


---------- Forwarded message ----------
From: quinonero juan manuel <jumaqu at yahoo.es>
Date: 25-Mar-2007 02:45
Subject: [GRASS-user] Creation of a DEM
To: grassuser at grass.itc.it


1.- You have to transform the vector information to a rast layer, you can do
it using the comand v.to.rast, baut before you have to determine the cell
resolution using for example g.region res=meters

2.- If you wsnt to create a good DEM you have to change the units of the
rast layer created, Only have to convert this layer from meter to centimeter
using r,mapcalc 'cm_layer=rast_meter*100.00'. That's for obtain a good
relation betwen horizontal and vertical resolution.

3.- Now you have to use an interpolatión method to create a DEM continous
surface. There are several methods, the commonest is r.surf.contour tat use
a lineal interpolation. If you use this command you must use the option -f
and it'll build faster, dont forget this point!!!!

4.- Finally you have to transform the results to the correct units usin
r.mapcalc 'final_DEM=cm_DEM/100.00'


If you want to generate a DEM usin another interpolation methods please
ask!!

Sorry for my english

Juanma

*megha shyam <capt_lms at yahoo.co.in>* escribió:

Please help me in creation of DEM.i have a vector layer contaning contour
information.How to create a DEM model  of this.Can you tell me the
stpes tobe followed

shyam

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