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Re: [udig-devel] 'Derived' or 'virtual' map layers / catalog contents
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Adrian Custer ha scritto:
Hey all,
I'm wondering if it's possible to create content that depends in a fixed
way on already existing content. For example, could we have layers which
are ('same as layer xxx but with points shifted 100meters to the
northwest')? Obviously, in that case, we would want to allow full affine
shifts, or even "rubber sheeting" algorithms. One could extend the idea
to be LayerB = buffer(LayerA, 300m) or similar constructs. The basic
idea is that there is a layer that looks to another for its contents.
This could be done either (or both) at the layer or the catalog level.
Do such 'dependent' layers already exist?
Not that I know of. We would need to build a layer as a dynamic result
from a graph of transformations
applied to a set of input layers, which is something I did in the past
with other tools (Grass + Autodesk Map + VB6).
It would be very nice to build something like this with uDig, I believe
what is blocking people
from doing it is:
* other priorities
* lack of a good defined operations models on the geotools side
* scary JTS performance on real world data, at least for boolean
operations between vector layers
(aka too slow to be used in practice...)
Cheers
Andrea Aime
