[GRASS-user] Extracting the external boundary of a vector file

[Edward Tomlinson]

Hi list,

I have a whole bunch of data from an RTK GPS. File exists as a MapInfo file.
Imports into grass fine with area and centroids.

My problem is however, i want to create another vector file that contains
the mask or the external (an internal island) boundary.

I have been able to create the external boundary fine through the following.
v.category (delete categories)
v.category (add category as 1 for all)
v.dissolve (combine all boundaries with common category)

This is great and works fine for the external boundary. However there is
meant to be an island in there. Somewhere along the way (i think after the
second call to v.category) it fills that island in.

Has anyone got any hints or ideas?

Essentially i am trying to create this vector to generate a mask for further
interpolation of the point heights. I am assuming that i need this island
removed (as there is no point data for it) otherwise it is going to effect
the interpolation.

Thanks for your time.
Ed
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