[GRASS-dev] v.what and spatial index

[Moritz Lennert]

Glynn Clements wrote:
> Moritz Lennert wrote:
> 
>>>> However, v.what does not have an interactive mode (that's the whole idea 
>>>> of v.what so it fits better into the GUI). This means that since it 
>>>> builds the spatial index everytime you call it, everytime you use the 
>>>> query tool you get the building of the spatial index.
>>>>
>>>> Now, I see several options from here:
>>>> - Change the query tool in the GUI so that it collects points and then 
>>>> sends the whole series to v.what. This has the big disadvantage that you 
>>>> don't see the results of your clicks immediately (i.e. you "blindly" 
>>>> click on a series of points and then push "go" to see the results for 
>>>> all of these points). It still means that whenever you resuse the query 
>>>> tool spatial index gets rebuilt which can be very annoying if you have 
>>>> to query information out of a map. So, even though this might be a 
>>>> temporary "solution", I don't find it very satisfactory.
>>>>
>>>> - Reimplement an interactive version of v.what, or rather make it 
>>>> possible to use d.what.vect from the GUI. This would probably mean 
>>>> recoding d.what.vect in whatever the GUI language and call GRASS library 
>>>> functions from there.
>>> The obvious approach is to extend v.what to allow coordinates to be
>>> read from stdin.
>> How would this change from the first approach (if v.what could easily be 
>> made to accept multiple coordinates) ? This would again mean 'blindly' 
>> collecting points before seeing the results, or having to call v.what 
>> multiple times.
> 
> v.what would read one coordinate pair, perform the lookup, write out
> the result(s), repeat until EOF.
> 
> gis.m would start one v.what process; each time you click the mouse
> button, it would send the coordinates to the v.what process, read the
> result, then display it. It would need to restart v.what if the set of
> maps changed, but could use a single process to look up multiple
> points.
> 

Here's my attempt at applying what you suggest. It's not very 
complicated, and seems to work fine here, but I'd appreciate if someone 
could check that I didn't do anything wrong before committing.

Now we will have to change the query function in the gis manager (from 
line 1474 of gui/tcltk/gis.m/mapcanvas.tcl) to use v.what with the -s 
flag and to provide continuous flow of coordinates and an EOF at the 
end. Michael, can you do this ? Or could someone tell me in rough lines 
how this can be done ?

Moritz
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