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
