Hello,
Just subscribed to the GRASS List. I installed GRASS yesterday and got pretty far with it, despite not having a GIS or a UNIX background.
Two questions:
(1) Can GRASS's "Build polylines from line segments" join line segments based on a common attribute in a table? For example, if the table has "street name" as a column, can street segments be joined together that share the same name attribute?
(2) Does GRASS have a way of concatenating two columns of data in a table? If one column is FENAME and another is FETYPE, can a new column be built that has both FENAME and FETYPE values (but separated by a space)?
Thanks for you help.
Steven Gordon
On 9/5/05, Steven Gordon <sg@cartagram.com> wrote:
Hello,
Just subscribed to the GRASS List. I installed GRASS yesterday and
got pretty far with it, despite not having a GIS or a UNIX background.
Two questions:
(1) Can GRASS's "Build polylines from line segments" join line
segments based on a common attribute in a table? For example, if the
table has "street name" as a column, can street segments be joined
together that share the same name attribute?
You have to write small script and cycle through all unique attributes, example:
v.in.ascii -e output=viapri_pol
for CODE in `echo "select distinct str_cd from viapri" | db.select -c`
do
v.extract -t input=viapri output=tmp0 where="str_cd = $CODE"
v.build.polylines input=tmp0 output=tmp1
v.category input=tmp1 output=tmp2 option=del
v.category input=tmp2 output=tmp3 layer=2 cat=$CODE step=0
v.patch -a input=tmp3 output=viapri_pol
done
(In this case str_cd is integer so it can be used as cat.)
(2) Does GRASS have a way of concatenating two columns of data in a
table? If one column is FENAME and another is FETYPE, can a new
column be built that has both FENAME and FETYPE values (but separated
by a space)?
Not with DBF driver, with Postgres usualy it is not necessary to
create a new column because you can use directly 'col1 || col2'
as GRASS option.
Radim
Thanks for you help.
Steven Gordon