[Tilecache] tiles for no-data areas

Stephen Woodbridge woodbri at swoodbridge.com
Wed Dec 1 20:15:12 EST 2010

On 12/1/2010 8:08 PM, Richard Greenwood wrote:
> I am not sure of the correct term for my question (which may be why my
> searches haven't been successful) so my apologies if this has been
> discussed previously.
> I have 8 layers of historic aerial photography from different years
> for a region. Unfortunately not all of the years cover all of the
> region. So a user might zoom into their area of interest viewing the
> 1945 imagery, then select the 1967 imagery which does not cover the
> area they are looking at, and see nothing but white. I'd like to
> notify the user that 1967 imagery is not available for the area that
> they are zoomed into. Something like Google Maps' notice that imagery
> is not available at the scale you are viewing.
> One idea I have is to create a vector layer for the no-data areas of
> each layer/year and label it appropriately. If I tilecache the layer I
> would eventually end up with many tiles that said the same thing, e.g.
> "1967 imagery is not available in this area". Which seems rather a
> waste. I could not run the vector layer thru tilecache and avoid that
> problem.
> I wondering if there is a more elegant solution to my problem.
> Thanks for reading.
> Rich

This is typically done by setting up an apache 404 handler that returns 
a single custom images. I'm not sure if tilecache has something similar 
built into it.

-Steve W

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