[GRASS-dev] vector large file support

[Markus Metz]

Glynn Clements wrote:
> Markus Metz wrote:
>
>   
>> BTW, display of grass7 with cairo appears to be half the speed of 
>> grass65, I think it was faster last week (can't remember the revision). 
>> Not sure if this justifies a complaint.
>>     
>
> Almost everything related to display has changed between 6.x and 7.0.
>
> One relatively recent change that may cause a slow-down is that the
> display library no longer tries to automatically simplify vectors
> (reduce consecutive short line segments with a single segment). This
> could have a significant impact when viewing detailed vectors at low
> zoom.
>   
OK. It does have a significant impact when viewing detailed vectors at 
low zoom (relatively detailed: 25MB coor, 31MB topo, not that large but 
complicated topology). I can't see a speed difference with small 
vectors. That just got me by surprise because I was used to a 7.0 
display that's faster, better, nicer than the 6.x display. Usually, the 
screen resolution can't represent that detail (same for raster map 
display), but I guess it is more correct to try to display all detail.

BTW, I'm testing LFS enabled vector libs in 7.0. So far it compiles as 
good or bad as before on Linux 32bit with and without --enable-largefile 
and on Linux 64bit with --enable-largefile. The test in 
lib/vector/diglib is not passed when compiling on Linux64bit without 
--enable-largefile, but the libs work anyway. I did not have to increase 
any of the version numbers, the vectors are fully backwards compatible, 
tested with 6.4.0RC3. It would be safer to change that though, and 
change the layout of the topo and cidx file.

IMHO LFS support for vector libs is not necessarily good, currently. In 
order to manipulate large vectors, a very fast CPU, fast hard drives and 
lots of RAM is needed, or a lot of patience, because it can take days or 
weeks to run modules with large vectors as input. That speed issue may 
change in the future, and I would regard LFS support in the vector libs 
as an investment in the future. Maybe I should rather try to fix bugs 
than to add new features...