[GRASS-dev] vector large file support

[Glynn Clements]

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.

Part of the problem is that a driver can generate either raster output
(PPM, PNG, etc) or vector output (PDF, PS, SVG), and the higher levels
don't know which is the case. For vector output, there is no obvious
threshold below which additional detail becomes unnecessary.

The display library has a function, D_set_reduction(), which will
merge adjacent line segments which are below the specified size, but
nothing uses it yet.

-- 
Glynn Clements <glynn at gclements.plus.com>