[Mapserver-users] Recommendations for multiple query of invisible layers.

[Ed McNierney]

Jason -

You should already be using a TILEINDEX to index your orthophotos.
Since your TILEINDEX is a shapefile with a polygon for each ortho, you
can create a separate layer using a DATA statement with the same
shapefile.  Then you can do your spatial query on that layer; you don't
have to display it.

It sounds like you haven't yet discovered TILEINDEX or aren't using it,
however, and you should.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com
-----Original Message-----
From: Jason M. Nielsen [mailto:jnielsen at aero-graphics.com] 
Sent: Friday, February 06, 2004 5:32 PM
To: mapserver-users at lists.gis.umn.edu
Subject: [Mapserver-users] Recommendations for multiple query of
invisible layers.

I have a map currently consisting of mosaiced orthographic imagery
covering an entire region. This is setup and working.

I also have data indicating the centers of photos covering this area. In
addition I have attributes for each photo consisting of scale, flight
angle, etc.

These photos all overlap.

What I would like to do is be able to query an area inside of mapserver
and have it return information about each photo that intersects with the
query region.

First thought was to create a shape file representing the bounding box
of each photo and have all the desired attributes attached to this file.
Then I could simply query that layer (containing that shape file) and
print the returned attributes.

The first issue I thought would occure with this is I do not want these
bounding boxes visible on the map being displayed in mapserver. Is it
possible to perform a query on a layer without having it visible?

The second idea was to put just the center points etc into a postgis db.
At some point the bounding boxes would be automatically calculated based
off of the center photo coordinate, scale, pixel size, x+y pixel size of
imagery, etc.
These pre or post created bounding boxes would then be what are queried
in order to determine intersection. They in turn would have to be linked
back to the center points in order to get the "metadata" sought after.

>From my crude diagram below you can see that a query could result in
either a single photo being returned or quite possibly even if the query
box falls only within one photo it could return two or more as well.
There could be any number of photos in a line overlapping and they would
be overlapping on all four sides with other photos accept the photos on
the very outter edges will normally not have any overlapping imagery to
their outside(direction from center of project).

001 : photo 1
002 : photo 2
--- : edge of photo
|   : edge of photo
+   : photo center point
=== : overlap area of two photos 

      001    002
-------========--------
|      |      |       |
|      |      |       |
|      +      +       |
|      |      |       |
|      |      |       |
-------========--------

Anyhow, the real question here is wether anyone has recommendations on
the basic method for doing this? ie: Are the lines Im thinking along a
decent method by which to accomplish this or am I on the wrong track or
making it more difficult than it really is etc.

Thanks, Jason.


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