Hi,
Recent work with Extract Layers by Geometry Type, and improving OpenJump's
support for very large selections, has convinced me that JUMP needs a
mechanism for dealing with subsets of large layers. Although the selection
mechanism is very flexible, it is very expensive in terms of memory and
processing. To seem what I mean, consider Arnd's million point layer
problem. To break the layer into more manageable pieces, he tried to select
some of the points and move them to another layer. When this is done with
such a large selection, the UI must build gigantic data structures. The
result is an extremely slow response or an out of memory error.
An approach that might work for some problems is to use the Fence tool to
indicate a subset of the data that can be used in place of a selection. The
advantage is that no data structures are needed and there are no selection
handles to draw. I was thinking of producing another Layer Extract plugin
that would extract features in the Fence to a new layer. By coding support
methods in a utility class, we could gradually add support for "features in
fence" subsets to the other tools.
What do you think?
regards,
Larry Becker
--
http://amusingprogrammer.blogspot.com/
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