[udig-devel] 'Derived' or 'virtual' map layers / catalog contents

[Bryan Hall]

Quoting Adrian Custer <acuster at gmail.com>:

> In a similar way, would it be possible to 'cache' the content of a WMS
> for a defined extent? Given that WMS's are often images, and that
> network latency is a problem, I'd like to get the data locally, rather
> than getting it remotely for each pan/shift. Would it be relatively
> straight forward to implement a context menu entry that did "if the size
> is reasonable (under 200megs), get the highest resolution image for the
> WMS source for the current extent of the map and cache that as a new, on
> disk, catalog source"?

Adrian,

I think these ideas have merit.

As a start, it would make sense to always bring back an image about 2.5 times
the size of the current display, so that panning at the same resolution 
will be
somewhat transparent.

Next, zooms in or out (within a reasonable range) could re-use what is 
currently
available (local disk cache) to show "something" before the new image is
returned. Zooming in is easy, and just stretches the pixels. Zooming out
shrinks the bitmap, but if the 2.5 area is already available, for a .5x zoom
out it all still covers the current display area.

Of course, most of this goes back to not having a local cache to "mine", which
is something I've discussed previously (and which we've requested as a Google
summer project).

Bryan