[GRASS-user] using v.to.rast

[Johannes Radinger]

Hi Janet,

if you choose "use=attr" then the value of the
attribute you set with "column=xxx" is used
as the value for the raster pixel. You can check
your attribute  table to find out which attribute values
are assign to each road section.

If you just want a "fix value" for each raster pixel of the road,
 you have to set "use=val" and then
provide a value you want (value=xxx).

So it depends what you're looking for. Which values
do you want to be assigned to you road-pixel in the raster format?

best regards,
Johannes

Am 14.03.2012 um 07:29 schrieb Janet Choate:

> Hi users,
> i've read the help and other posts regarding v.to.rast, but i'm still not piecing it all together and would appreciate some help.
> i have a vector map of roads that i want to convert to a raster, so it is lines.  v.support - fine, but i can not figure out what i need to do with v.digit (and if v.digit is necessary), don't know how to use.  after running v.support, if i just run v.to.rast as:
> 
> v.to.rast input=roads output=roads
> ERROR: Column parameter missing (or use value parameter)
> 
> but if i run as:
> v.to.rast input=roads output=roads5 use=attr column=ROADNR
> (or column=CODE, etc..)
> 
> then i get a raster.  values of the raster differ based on what column i choose.  so my question is, how do i choose the column, and how do i know what to set use= to (attr,cat,val,z,dir)
> 
> running db.describe on the road vector, i get the following info:
> db.describe -c table=roads
> ncols: 14
> nrows: 383
> Column 1: cat:INTEGER:11
> Column 2: UserId:INTEGER:11
> Column 3: FNODE_:INTEGER:11
> Column 4: TNODE_:INTEGER:11
> Column 5: LPOLY_:INTEGER:11
> Column 6: RPOLY_:INTEGER:11
> Column 7: LENGTH:DOUBLE PRECISION:20
> Column 8: GI00701_:INTEGER:11
> Column 9: GI00701_ID:INTEGER:11
> Column 10: YEAR:INTEGER:11
> Column 11: ROADDEC:INTEGER:11
> Column 12: CODE:INTEGER:11
> Column 13: STAT:CHARACTER:1
> Column 14: ROADNR:INTEGER:11
> 
> if anyone can please advise the process of turning a vector into a raster, i.e. what commands are necessary first and how to apply them, i would really appreciate it.
> thank you, 
> Janet
> 
> 
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