[GRASS-user] shapefile, TIGER, or what for a dlg that is stored in .e00 format

Nikos Alexandris nikos.alexandris at felis.uni-freiburg.de
Wed Jul 8 20:38:07 EDT 2009

stephen sefick wrote:

> I am trying to make a DEM from contour lines downloaded from here
> http://csat.er.usgs.gov/statewide/layers/contours.html
> I converted this to a shape file

You don't need to convert it to  Shapefile. You can import vector .e00
files directly in GRASS using v.in.e00. Note that you need to have to
programs installed: "avce00" and "e00compr".

> reprojected it,

why? from what to what CRS? Did you not create a location based on the
coordinate reference system in which the data are referenced? Did you
have any success with the "GRID" data, if of course you tried?

>  and then v.to.rast use=value and got out a raster with a range of 1
> to 1.

That is so because the v.to.rast module expects from the user to define
the "value" incase you use the "use=value" parameter. If the user does
not define the "value" then "value=1" is taken as default. Please read
the respective manual(s) [1].

I suppose that "v.to.rast use=val value=SomeValue" is not what you want.
Giving a fixed value to all of the vector features that will be
rasterized wont be useful if you want to play further with the data
(e.g. create a DEM as you mention above).

> How do I do this?

# I downloaed the data you mention and did the following:
v.in.e00 contours.e00 vect=contours type=line

# check attribute table
v.info -c contours

v.info -c contours
Displaying column types/names for database connection of layer 1:

# match region ## I am unsure about the resolution (=look at the
original data resolution from which the contours derived)
g.region vect=contours res=SomeResolutionValue -pa

# the last column is probably of your interest, so
v.to.rast use=val value=attr col=ELEV

Perhaps you do not even need to rasterise. Have a look at v.surf.rst
[2]. Of course I am no expert with DEM's, v.surf.rst might not be what
you need.

Kind regards, Nikos

[1] http://grass.osgeo.org/grass64/manuals/html64_user/v.to.rast.html

[2] http://grass.osgeo.org/grass64/manuals/html64_user/v.surf.rst.html

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