Re: Mutable Datasets

• To: "P. Tewson" <ptewson@xxxxxxxxxxxxxxxx>
• Subject: Re: Mutable Datasets
• From: Bill Hibbard <billh@xxxxxxxxxxxxx>
• Date: Wed, 10 Jul 2002 14:54:11 -0500 (CDT)

Hi Patrick,

Your approach sounds about right. In addition to
MutableIrregularSet (or MutableIrregularSet*D), you'll
need something like MutableDelaunayCustom (as you add
points you should add triangles or tetrahedra incrementally
to avoid the huge time penalty of re-running Delaunay
algorithms) and MutableFlatField.

You can probably do this by copying code from the existing
classes and carefully modifying a small but carefully
chosen subset of that code.

Of course, you'll also need to be careful about how you
access these objects from multiple Threads. Each CellImpl
and DisplayImpl has a Thread, and without the general Data
imuutability this mailing list would see lots of mysterious
Thread errors (the dog that didn't bark in the night).

Good luck,
Bill
----------------------------------------------------------
Bill Hibbard, SSEC, 1225 W. Dayton St., Madison, WI  53706
hibbard@xxxxxxxxxxxxxxxxx  608-263-4427  fax: 608-263-6738
http://www.ssec.wisc.edu/~billh/vis.html


On Wed, 10 Jul 2002, P. Tewson wrote:

> Hello,
>
> I'm working on a geo-referenced database that stores environmental
> information for ocean environments. As the project progresses, it's
> becomming more and more clear that what we really need is a solid data
> model on which to base the storage and interface. Having to handle each
> data type separately is slowing development.
>
> Since I had used VisAD in the past, I started looking into using the VisAD
> data model as a basis for our database. Since visualizing the data is not
> a priority, we don't need to make use of most of VisAD's visualization
> capability -- just the solid data model. However, I'm running into
> problems with the immutability of the datasets. Since our data is
> geo-referenced but not regular, I was planning on using an IrregularSet to
> store information. However, due to the immutability of all of the Set
> classes, adding a single new entry to the thousands already stored seems
> like it would require creating entirely new domain sample arrays for the
> old points + single new point and creating an entirely new set around that
> new sample array.
>
> So, to finally get to the question, is there anything fundamentally wrong
> with the ideal of rolling our own MutableIrregularSet class that mimics
> the behavior of the IrregularSet class except for allowing dynamic changes
> to the domain samples? We would probably have to start sub-classing fairly
> far back in the hierarchy (around SimpleSet, it looks like) and replace
> the arrays with Vectors or Lists (which will be bad for performance but
> hopefully not critical since we aren't visualizing). Would the visad
> Delaunay class support a more dynamic approach, or would that require
> custom development as well, creating a MutableDelaunay class? I suppose a
> MutableFlatField would also be neccessary
>
> Or are we barking up the wrong tree? Is there an easier solution to this
> problem, or a package with a more suitable data model?
>
> Thanks for your help,
>
> Patrick Tewson
> UW Applied Physics Lab
>
>

• References:
  • Mutable Datasets
    • From: P. Tewson