Hi all,
I have tried to make topology building in grass7 a bit faster, with
limited success. Some functions are now a bit faster, but there are no
drastic changes. Some other functions are now a bit slower, and there I
would like to know if there are objections against these changes.
The first change causing a little slow down is in diglib: memory of no
longer used structures is freed. That was mentioned as a TODO in the
source code, probably by Radim. All I can see now is that cleaning time,
e.g. v.in.ogr of a polygon vector, increases from e.g. 15m30s to 15m35s,
IOW speed loss is in this case about 0.5%, but memory consumption is not
really lower, even when cleaning large vectors with many areas (>
50,000) where many structures should be freed. The new functions
dig_free_node(), dig_free_line(), dig_free_area(), and dig_free_isle()
in diglib/struct_alloc.c are called from within plus_line.c and
plus_area.c. Maybe someone can have a look at the new functions in
struct_alloc.c to check if I made a mistake? AFAIKT, there is no obvious
mistake, resulting vectors are identical in my cleaning tests, no
warnings or errors.
Another similar slow down (about 0.5%) is caused by G_percent which I
added to all cleaning functions. The reasoning is that users may wonder
if anything is happening at all when importing a large polygon vector
with v.in.ogr or cleaning a large vector, and G_percent shows that there
is something happening. I find that reassuring to know.
In short, grass7 is still about as fast as grass6 with regard to
cleaning vectors (should be a bit faster with building topology, only
noticeable with really large vectors), but gives a bit more feedback on
the progress. The vector API as well as the vector format is unchanged.
If there are objections against these changes, I will revert them.
Regards,
Markus M
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