[GRASS-user] Re: How to best access hundreds of orthophotos -- mapserver as WMS server?

[Hamish]

Hamish:
> > an idea: write a little script to make a vector coversheet index.
> > maybe output that with the HTMLMAP driver for an interactive web
> > browser pull up.
> >
> > I am not sure, but I think v.patch does not clean topology so
> > overlap may be ok.

Ivan:
> Wouldn't it be better to save non-overlapping parts and an
> intersection as separate polygons?  A separate attribute will be
> needed to store the list of IDs of the covering images.

see overlapping polygon example at:
  http://grass.ibiblio.org/screenshots/vector.php


>  > # store current region
>  > g.region save=old_region
> 
> 	It makes me wonder each time I see such a fragile construct like
> 	this, will GRASS ever support overriding the region
> 	``temporarily''?  (E. g., via a command line argument, or an
> 	environment variable.)

there is, see GRASS_REGION and WIND_OVERRIDE shell variables:
  http://grass.ibiblio.org/grass63/manuals/html63_user/variables.html

but saving & restoring g.region isn't need for this task, it is just
being nice leaving the place as you found it. The script is not
dependent on the starting region. And I fail to see how that's fragile?
No more fragile than trusting anything else written to the disk.

> >   v.in.region out="${MAP}_box"
> 
> Oh, perhaps `v.in.region' could be patched to print the category
> of the vector feature it creates (if requested)?

ie have a new cat= option added to set the cat number. (default "1")
right now it always creates as cat 1.

> I guess, this usage pattern is quite common for `v.in.region'?

no idea. I've used the module a lot and this is first time I've had to
worry about that.


> And, could there be something a bit more clever than storing the
> region of the image as a vector feature?

the user can get as complicated as they like..

> A combination of downsampling, `r.mapcalc' (to obtain the fill mask),
> and `r.contour', may be?

r.contour is not so good for ortho photos or high resolution land use
map with many small areas. But again, up to the user....


> >   v.patch in=map_index_old,"${MAP}_box" out=map_index
> 
> May there `v.patch -a' be used instead?  Like:
> 
> v.patch -a in="${MAP}_box" output=map_index

yes, that's the correct way.


Hamish




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