[GRASS-user] Intersections on World Map

[Martin Bley]

Hi Ivan,
hi folks,

On Sun, Nov 04, 2007 at 03:25:17PM +0100, ivan marchesini wrote:
> [...]
> this to explain the results of v.build...
thanks a lot for your detailed explanation.

> but this doesn't explain the reason of the strange overlay...
I suspect, v.overlay using operator "AND" is buggy. I found a bug report
(ID #5427) describing this behavior, which has still open status. Using 
operator "NOT", v.overlay will work properly. In my case that solves the
issue. 

> why did you try to do all the intersection line for line...
> why didn't you create a single "lines map" that contain all the
> latitudes and then perform the overlay?
Well, I'm new to GRASS and I did it this way, because don't know to do 
better this time - I'll work on it ;) 
My task is the following: I would like to figure out for every single 
latitude, how much of it is covered by ocean surface and how much is
covered by a continent. So, I want a table like this

Lat|Ocean length (meters)|total length (meters)
[...]
10N|???|39470.171
[...]

Total length I calculated using a perl script. To get the "Ocean
Length", I export the vector maps with the intersections (using points),
afterwards I use another perl script, to calc length of the segments and
finally the sum of all segments. 

That's why I didn't use a single "lines map" - just to keep things
clearly arranged. 

My next excercise will be connection those segments lengths to the GRASS
database. 

Regards,
Martin