[Qgis-developer] Re: Problem in shapefiles rendering

bargi john bargi1981 at gmail.com
Mon Jun 23 00:32:28 EDT 2008

Hi Martin,

Thanks for reply......

>But in case you have to transform just of some data, it's possible
>that your data might be incorrect.

What does this mean ??
Actually the shapefiles I am using is downloaded from ibcca.
And over though, how QGIS is rendering it properly ?
Did u mean that I have to do coordinate Transformation on features before
they are drawn ?
Actually I want to know that how QGIS is able to draw the shapefiles
correctly and not my application ?
Is there special code for this since the way QGraphicsView is created is
same in QGIS and in my application.


On Sat, Jun 21, 2008 at 4:34 PM, Martin Dobias <wonder.sk at gmail.com> wrote:

> On Thu, Jun 19, 2008 at 6:43 AM, bargi john <bargi1981 at gmail.com> wrote:
> > Hi Martin,
> >
> > Thanks for reply......
> > Actually the application I am working on is similar to QGIS in which
> > shapefiles are rendered using QT.
> > In between, I researched on the problem and find out that this issue is
> > related to QGraphicsView architecture.
> > In essence, when QGraphicsView is created , it create with origin(0,0) at
> > top left corner. Due to which the positive quadrant is downwards  and
> > negative upwards ( What I think ) due to which when shapefiles are
> rendered
> > according the coordinates position they draw in downward direction(
> because
> > coordinates of shapefiles are positive) and they appear to inverted.I
> found
> > scaling as a clutch which invert the the GraphicsView and line and
> polygon
> > shapefiles are drawn properly but it invert the point shapefile.
> > Due to this I reached to the possible solution that can be applied on
> > application:-
> >
> > --- One way can be that we create the QGraphicsView with origin(0,0) at
> > bottom left corner.Due to this we will get the proper coordinate system
> for
> > rendering. I have tried on it but not able to find the sol. how it will
> be
> > implemented.
> Actually, coordinates can be both positive and negative: with
> unprojected coordinates on earth:
> - x in range [-180, 180]
> - y in range [-90,90]
> northern hemisphere: y positive
> eastern hemisphere: x positive
> But in case you have to transform just of some data, it's possible
> that your data might be incorrect.
> Martin
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