[GRASS-user] "Automatic" redraw of map display in 6.4 when underlying raster changes?

Glynn Clements glynn at gclements.plus.com
Thu Oct 6 23:22:21 EDT 2011

Rainer M Krug wrote:

> > Monitoring the filesystem is likely to be unreliable, as there's no
> > straightforward way to determine when files are in a consistent state.
> Thanks for pointing this out and saving me some work - otherwise I might
> have chosen that path...

Also, doing this at the library level would have similar issues,
albeit less severe.

E.g. when a module finishes writing the actual raster data (i.e. 
G_close_cell() or Rast_close()), often the next thing it does is to
write metadata (categories, colour table, history). There is no
specific "event" which signals that the output raster is "complete".

Generating notifications on "close" operations would ensure that
individual files are consistent, but that doesn't mean that the raster
as a whole is consistent.

This is something that has been discussed in the past, but without
resolution. Improvements in this area are certainly desirable; e.g. 
reading a map in another mapset relies upon luck, as there is no
mechanism to ensure that the owner of that mapset isn't modifying the
map in question at the time. Unfortunately, the issues are complex,
making it hard to decide what should be done, let alone doing it.

Glynn Clements <glynn at gclements.plus.com>

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