[Qgis-user] QGIS performance problem

[Andreas Neumann]

Hi Brent,

I have similar behaviour. It happens if polygons with lots of vertices 
are involved. Things get even worse if you try to print this data with 
high resolution.

Marco Hugentobler and Jürgen Fischer are already working on this issue 
these days. They can also better explain the issues we are running into 
- seems to be qt and clipping related when bounding boxes of big 
polygons are touched when zooming in or printing on high resolutions.

I am glad to hear that I am not the only person experiencing these 
problems - seems to be a real issue.

Andreas

pcreso at pcreso.com wrote:
> Hi,
>
> I have a PostGIS table & shapefile of the New Zealand coast (1:50,000)
>
> If I open this table it plots in a fraction of a second, pretty much as expected, with similar speeds for both the shapefile & table.
>
> However, if I zoom in, the redraw takes three minutes or more. 
>
> While I'm waiting for the refresh, Qgis is showing 100% cpu load, postgres isn't showing at all (top). On an AMD dual core 3.2Ghz cpu with 8Gb ram it should not take anything like this long, and with earlier versions of Qgis (pre 1.0) it was much faster.
>
> Performance is similar with both table & shapefile data sources, so it does not seem Postgres related.
>
> However, plotting lines, points or polygons with tens of thousands of features rendered works well, it seems to primarily be polygons with many vertices (not even any holes) that are the problem.
>
> OpenSuse 11.1, Qgis 1.2.0, Postgis table described below, only 3 features/records, indexed & vacuumed.
>
>
> Does anyone have any idea what may be the issue?
>
> I can provide an ssh login if anyone wants to test this for themselves.
>
>
> Thanks,
>
>    Brent Wood 
>
>
>
>
>
>
>                                  Table "public.coast_poly"
>  Column  |         Type          |                        Modifiers                         
> ---------+-----------------------+----------------------------------------------------------
>  gid     | integer               | not null default nextval('coast_poly_gid_seq'::regclass)
>  id      | bigint                |
>  fid     | bigint                |
>  name    | character varying(42) |
>  geom_ll | geometry              |
> Indexes:
>     "coast_poly_pkey" PRIMARY KEY, btree (gid)
>     "coast_poly_geom_ll_gist" gist (geom_ll)
> Check constraints:
>     "enforce_dims_geom_ll" CHECK (ndims(geom_ll) = 2)
>     "enforce_geotype_geom_ll" CHECK (geometrytype(geom_ll) = 'MULTIPOLYGON'::text OR geom_ll IS NULL)
>     "enforce_srid_geom_ll" CHECK (srid(geom_ll) = 4326)
>
>
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