[Tilesathome] Lowzoom approaches. Feedback appreciated.

[Alan Millar]

As 80n mentioned, the current lowzoom process is a combination of two
steps: rendering captions and then stitching and compositing tiles.

>> 1) Turn off automatic lowzooms. This is trivial and you will have to
>> upload the lowzoom 'tiles','captionless', and 'caption' tiles just as
>> before, with the only change that a lowzoom tileset spans z6-11. All
>> the existing tools will continue to work.

I think this is OK to do.  I see it as a short-term fix until we get
choice 2 working.  I think I have done most of the z8 generating lately. 
I probably will not bother adapting my local scripts and tile lists to z6,
but spend my time figuring out choice number 2:

>> 2) Live with the suboptimal lowzoom stitching until I have fixed up
>> things and found better ways to create nice looking low zoom tiles and
>> to combine them with the caption layer. This could easily take a week
>> or 2.

I think this is OK.  Either way it should not be too long until the
server-side stitching is fixed.  We lived with messy lowzoom layers for
months; another week or two probably won't hurt anything.

>> 3) Somebody (not me) modifies the tah client to be able to process
>> lowzoom requests (integrating the existing lowzoom generation
>> tool). The server, knowing which lowzoom tiles need to be updated can
>> then simply issue lowzoom requests. These would be processed by the
>> clients and uploaded as rgular lowzoom tilesets. I actually favor this
>> solution, but don't vote for it, if you aren't prepared to code it :-).

I don't think the client should do everything, but I think the client
should do the caption layer.  The client already works in loop mode for
handling z8 requests, if you have it configured for lowzoom.  It will just
render the caption layer but not do the compositing.  There weren't many
server-side requests for z8 renders, and since they didn't do the
stitching they weren't much good, so it has been pretty much ignored.  But
now that we will have server-side stitching, this will become useful once
again.  Changing from z8 to z6 should not be difficult, I expect.

- Alan