'field' option is used as layer identifier in 5.7. Each
vector can contain more layers, for example
field=1 : forests
field=2 : lakes
Unfortunately the name 'field' is commonly used for table
columns, so it is quite confusing. My suggestion is
to use option key 'layer' instead of 'field'.
Radim
Radim,
I'm glad you brought this up. It took me awhile to even figure out what
"field" meant, given my long association with databases. I agree that the
name should be changed. But let me ask to make sure exactly how 'field'
works to make sure I do understand it correctly now.
A set of vectors (i.e., shapes in a single vector map) can be associated
with more than one attribute table. 'Field' makes the connection between the
vectors and each of the the attribute tables. Field1 connects to the default
table, while field2, field3... connect the same vectors to other tables.
If this is correct, I suggest using the term connection or link rather than
layers. Layer can often imply a different set of vector shapes.
However, if I still don't understand how this works I hope you can set me
straight.
Thanks.
On 11/13/04 4:09 AM, "Radim Blazek" <blazek@itc.it> wrote:
'field' option is used as layer identifier in 5.7. Each
vector can contain more layers, for example
field=1 : forests
field=2 : lakesUnfortunately the name 'field' is commonly used for table
columns, so it is quite confusing. My suggestion is
to use option key 'layer' instead of 'field'.Radim
____________________
C. Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
PO Box 872402
Arizona State University
Tempe, AZ 85287-2402
USA
Phone: 480-965-6262
Fax: 480-965-7671
www: <www.public.asu.edu/~cmbarton>
Michael Barton wrote:
Radim,
I'm glad you brought this up. It took me awhile to even figure out what
"field" meant, given my long association with databases. I agree that the
name should be changed. But let me ask to make sure exactly how 'field'
works to make sure I do understand it correctly now.A set of vectors (i.e., shapes in a single vector map) can be associated
with more than one attribute table. 'Field' makes the connection between the
vectors and each of the the attribute tables. Field1 connects to the default
table, while field2, field3... connect the same vectors to other tables.If this is correct, I suggest using the term connection or link rather than
layers. Layer can often imply a different set of vector shapes.However, if I still don't understand how this works I hope you can set me
straight.
It is possible to link one geometry to more tables, it is not
the typical case however. Usually, if more fields are used,
the different elements are linked to different tables.
For example, if a landcover map contains forests, lakes and
fields, each centroid is linked only to one table,
using one link. The tables have different structure.
That vector in GRASS is equivalent to for example 3 shapefiles,
3 layers: forests, lakes, field.
Export to simple feature results in 3 layers.
In QGIS (simple feature model), all GRASS features with the
same field are put to one layer.
The name link is not appropriate, because the field can be
a link, but it can be also used in the vector, but there
are no connected tables.
Have you evere played with?: http://mpa.itc.it/radim/g51/g51test-12-multi.tar.gz
Radim