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implementing Spatial Indexing in VB yogi 04-25-2005
Posted by yogi on April 25, 2005, 2:11 am
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 hi,

i am working on a GIS project which is composed of n number of data.

i have organised the spatial objects like point,line,polygon into my
proprietory data structure and used binary files for storing these
spatial objects.

Example : A single line object is a collection of several points which
can be ahighway or some other type of road. I have used an array to
hold the different line objects which get stored in binary files in
the line object structure(with no spatial indexing).

I am stucked with the situation in which i have to load only those
records which falls under my current viewport becoz no point in
loading all of the records which are not inside my current viewport
definition.i have researched on the net and came to know about the
spatial indexing and its types like quad tree, Rtree.I do not have
much idea about these data structures and its implementation in VB.

I need to create the spatial indexes based on Quad tree spatial
indexing while reading it from the binary file (so that i can organize
my data accordingly and read it through spatial indexes the next time
i fetch out the records from file) and therefore finally loading only
those data which falls under my current viewport into an array .My
proprietory structure of line object does not have any bounding
rectangle(MBR).

If any one has an idea about its implementation please write to me as
soon as possible. Would be keenly waiting for replies from u guys

Thanks

Yogi


Posted by Marc Pelletier on April 25, 2005, 4:45 pm
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 yogender_garg@hotmail.com (yogi) wrote in

> My
> proprietory structure of line object does not have any bounding
> rectangle(MBR).
>
>

Well... it seems to me that each object, and each node in the quadtree
needs an MBR. For a working example take a look at the shplib code.
Building quadtrees is implemented there, but last time I looked they
weren't being saved to disk.

This is fun stuff, good luck.

Marc Pelletier
Goldak Airborne Surveys


Posted by yogi on April 26, 2005, 5:53 am
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> yogender_garg@hotmail.com (yogi) wrote in
>
> > My
> > proprietory structure of line object does not have any bounding
> > rectangle(MBR).
> >
> >
>
> Well... it seems to me that each object, and each node in the quadtree
> needs an MBR. For a working example take a look at the shplib code.
> Building quadtrees is implemented there, but last time I looked they
> weren't being saved to disk.
>
> This is fun stuff, good luck.
>
> Marc Pelletier
> Goldak Airborne Surveys

hi Marc,

Thanks for ur reply.

I got ur point but the next tip i need from u is how to create the
MBR's for each and every record of spatial types(point,line,polygon)
or can spatial indexing be implemented without using MBR???

Is there any algorithm for creating the MBR.

Thanks

Yogi


Posted by Jatin on April 26, 2005, 7:06 am
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yogi wrote:
> hi Marc,
>
> Thanks for ur reply.
>
> I got ur point but the next tip i need from u is how to create the
> MBR's for each and every record of spatial types(point,line,polygon)
> or can spatial indexing be implemented without using MBR???
>
> Is there any algorithm for creating the MBR.
>
> Thanks
>
> Yogi

MBR is an axis aligned minumum bounding rectangle within which a given
geometry fits. So, given a geometry, scan its coordinates and determine
minX, minY, maxX amd maxY. That would define the MBR for that geometry.

Jatin
===============



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