[Qgis-developer] questions on rendering

[Martin Dobias]

On Tue, Sep 27, 2011 at 4:18 PM, Mohammed Rashad
<mohammedrashadkm at gmail.com> wrote:
> Hi All,
> I am developing tiled vector rendering in OSSIM. I like the Qgis vector
> rendering system
> point.shp contains 9,99,999 points which are generated by grass for using
> v.random and ~27MB in size
> roads.shp contains 2,28,068 linestrings and is ~50MB in size
> these point.shp and roads.shp data gets rendered in ~10 sec
> When I read vector using ogr and parse feature and draw point/linestring my
> application taking about 40 sec to render point.shp
> and
> I am using Qt4 with QPainter not QGraphicsView
> How came this time gap?

Most likely you have some inefficiencies in your implementation.

> i see Rtree and pal libs in src/core source code
> Does they have any role in rendering?

No - unless you also draw labels.

> Does QGIS Rendering uses threading?

No - only in threading branch which has not yet been integrated.

> How to get a minimal of QGIS code to hack it and build a new vector
> rendering because I need it to make it tiled rendering vectors?

You can use qgis_core library to do tiled drawing.

> How to improve performance in rendering without qgis?

Learn how to profile programs - i.e. get time spent in individual
functions, analyze the results and fix the places where most of the
time is spent.

Martin