[OAM-talk] a dramatically simplified technical proposal

[Laurence Penney]

Nothing wrong with using PNG only for (rare) edge tiles. This is the  
approach in Google Earth PhotoOverlay tile pyramids:

http://code.google.com/apis/kml/documentation/photos.html

For (rectangular) photos one might suggest that JPEG tiles of lesser  
dimensions than 256x256 might be better, but orthorectified imagery  
will, in general, have diagonal edges, so a PNG with transparent parts  
seems ideal to me.

- L

On 11 Nov 2009, at 15:42, Keith Jenkins wrote:

>>> Image tiles should be 256x256 pixels in 8- or 24-bit compressed  
>>> PNG format
>>
>> I understand the desire for transparency, but I'm not entirely sure
>> how we see it being used.
>
> I agree that JPEG makes more sense for imagery.  My guess is that the
> transparency info would be needed in order to merge tiles from
> different layers into a global layer.  For example, one layer might
> only cover half the tile.  Maybe there is another way to address this
> problem without depending on PNG transparency... perhaps by using the
> bounding box metadata?
>
> Keith