[GRASS-user] the performance of displaying vector attributes

[Moritz Lennert]

Hello Zbigniew,
(Cc to Michael and Glynn as they are currently busy reworking
d.vect.thematic)

On Fri, November 10, 2006 17:18, Zbigniew Perski wrote:
> Hi,
>
> I am facing now with following problem:
>
> I have a large databases of points (more 30 000). I would like to
> visualize them in colors according to different attributes using
> d.vect.thematc and also store rgb information in the GRASSRGB column. I
> noticed that both methods are incredibly slow. It is very frustrating
> since you have to zoom and wait ages for refreshing the monitor.

There are several performance issues with d.vect.thematic:

1) It is script-based and so if you have lots of points, it might take
longer to calculate classes and colours than a C-based version might
(although I don't know how much difference this would make).

2) Gis.m seems to consider it as a new command everytime you renew the
display in any way leading to all the calculations and rendering having to
be redone. If you have a lot of points, this takes time.

3) I'm not sure the way the database connections are handled in d.vect are
always the most efficient.

4) d.vect in itself is not the most efficient for plotting.

> My
> database is stored using db engine. I would like to ask you if storing
> the point database using different engine like postgresql or mysql will
> have any impact on the performance in displaying the GRASSRGB column?

As others have said, indexing will probably help you somehwat.

> Is there any other methods to speed-up the display performance in my
> case? I would like to add that I checked point displaying on various
> hardware combinations and I did not noticed any significant difference.
> It is always very slow.

I think the first important element would be to find a way to not rerun
d.vect.thematic at every zoom or refresh...

Moritz