Hi,
1. Transfering attributes from embedded points to the
thiessen polygons, is already possible, in two steps,
and have been using it.
Step one: Create thiessen polygons from points
Step two: Tools --> Analysis --> Spatial join of
geometries
This results in the polygons aquiring the attributes
from inscribed points.
2. UNION
UNION of two polygon layers is what is requested.( not
one polygon layer and a point layer)
A+B= C
the resulting C polygon layer to have
(a) both A and B's attributes, where they intersect
(b) Only A or B's attribute where they do not.
Similar function in GRASS GIS (pasted from its help)
'v.overlay allows the user to overlay two vector area
maps. The resulting output map has a merged
attribute-table. The origin column-names have a prefix
(a_ and b_) which results from the ainput- and
binput-map.'
***************************************
YOUR CAUTION
"what do you do if several feartures (i.e. points) are
contained within one polygon? which point do you
chose?"
I appreciate this problem. This involves a polygon
layer and a point layer not two polygon layers
***************************************
Cheers
Ravi KUmar
Hei Ravi,
> 3. Please consider making UNION of two layers by
adding
> both layer's attribute tables in the resulting
file.
> A + B = C (C contains a table with attributes of
both A and B
> where there is no intersection,
attributes are
not
> populated)
> Been trying to make an exercise on Mineral
prognostication,
> but is held up at this point as there is no
UNION.
this function should not be called union, but rather
merging as the
term
union in the manner we use it is derived from the OGC
simple features
standard. Further what you want is not that easy..
For instance: what do you do if several feartures
(i.e. points) are
contained within one polygon? which point do you
chose? The feature
works only if there is a one-to-one relation.
Basically I have programmed a similar function right
now for the
thiessen polygons.. but I am not sure if people are
aware of the
problems when using it...
what do others think..
Should I implement it despite my reservations?
Should I extend the "Transfer Attributes" function for
"intersection"?
Should we also rename Overlay.. to intersection?
PS: please move on with this discussion
[EMAIL PROTECTED]
Stefan
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