[GRASSLIST:4060] direction to nearest...?

[Alex Thorn]

Hi again.

Once again I ask for words of wisdom.

What I'd like to be able to do is to calculate the
direction from a point to the nearest cell that has a
given raster value (raster not important here, I just
assume that it is the best way to implement this). 
I've been looking over the available GRASS commands,
but haven't been able to find something that will do
quite what I want.  The commands dealing with
calculating flow seem related, although they call for
a continuous coverage (e.g. elevation), rather than
discrete data about a particular feature being present
or absent in a given cell.  

It seems that I ought to be able to get something
along the lines of the flow/drainage models to work if
I can generate a coverage in which each cell is
defined by its distance from a cell with the
appropriate raster value (I seem to remember reading
about something like this in one of the tutorials).  I
don't have a clear idea of the steps involved, though,
and was wondering if someone could give me pointers,
so that I don't end up pointlessly rediscovering the
wheel.

Thanks in advance,
Alex

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