Re: [GRASS-user] Using v.in.ascii to create elevation vector

[José María Michia]

2008/11/16 Kurt Springs [EMAIL PROTECTED]:
 Hi folks,

 I am trying to convert ascii files that I bought from the Irish Ordinance
 Survey in to GRASS vector format.  These are digital terrain models.  I want
 to eventually make a raster surface map and a 3d raster map out
 demonstrating where various archaeological sites are.

 The files the OSI has sent me have a heading set off with # on each line,
 then the data.  There are three columns, eventually x, y, z.  These are
 separated by a space.

I think you should remove the character # for all lines with data.

You must go from lines like these:

# x y z

To lineas like these:

x y z

You can do this, using the linux command sed. You must execute
something like these:

$ sed  's/^#\ *//g' datos_orig.xyz  datos.xyz


 Using v.in.ascii, I checked Create 3D file

 selected the input file, in this case 0834_10.DTM and typed the out put file
 osi0834.  The field separator was set to |.  I erased this, and left it
 blank. Input file format was set to point.

 I clicked on the Columns tab.  I left the SQL blank.  Left x=1 y=2  and set
 Z=3.

 When I hit run I got:

 Scanning input for column types...

 Maximum input row length: 33

 Maximum number of columns: 1

 Minimum number of columns: 1

 y column number  minimum last column number

 (incorrect field separator?)

 I put the | back and got the same error.

 I then set the input file format to standard and got:


 Unexpected data in vector head:

 [#]

 I have a lot of these to convert.  Can anyone give me any advice?

If I understood, you must delete the #. See my previous comment in
this message.

José María

 Kurt
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Re: [GRASS-user] Using v.in.ascii to create elevation vector

[Paul Kelly]

On Sun, 16 Nov 2008, Kurt Springs wrote:


Hi folks,

I am trying to convert ascii files that I bought from the Irish Ordinance 
Survey in to GRASS vector format.  These are digital terrain models.  I want 
to eventually make a raster surface map and a 3d raster map out demonstrating 
where various archaeological sites are.


The files the OSI has sent me have a heading set off with # on each line, 
then the data.  There are three columns, eventually x, y, z.  These are 
separated by a space.


Some years ago I obtained gridded DEM data from the Ordnance Survey of 
Northern Ireland, and I wonder if this was the same format. The two 
Ordnance Surveys in Ireland do seem to do a reasonable amount of 
cross-border co-operation. Anyway (I didn't actually use the gridded DEM 
data; they just sent me a sample to see if it would be useful for our 
purposes) the data I obtained was gridded at 50m resolution, i.e. it was 
already in raster format so as Hamish said could be directly imported as 
a raster. Could you maybe post a short sample of a few lines of the data 
format so that we can see the format exactly? ISTR (this was perhaps 6 
years ago so memory a little hazy) that I wrote a Perl script to process 
the DEM format - if it *is* the same format I could try digging it out for 
you.


What is the resolution of the data? There are global free elevation 
datasets with a better resolution than 50m these days. Also with the OSNI 
data I realised that it had just been interpolated from contours with some 
other GIS, and I decided I was much better interpolating my own DEM 
directly from vector contour maps using one of the superior algorithms in 
GRASS. I got the vector contour maps from OSNI in DXF format and imported 
them into GRASS with v.in.dxf. I would recommend this approach over 
pre-gridded DTM data if possible, as it gives you more control over 
interpolating a DEM that is most useful for your purposes.


Paul

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