working with shapefiles in Qwt

[swamyonline]

hi,
im trying to use a map in my Qt/ Qwt application. and im very immature in dealing with this. i would like to know ur suggestions regarding this. how can i use shapefiles (esri) of a perticular region in my application. or which is better, to use a SVG map or a shapefile? how can i use with Qwt Plots where my data is drawn over them in real time.. pls post your suggestions in this regard.. thanks in advance. bye

[Uwe]

AFAIR shapes are simply polygons. I would implement a custom plot item, that maps them into the coordinate system of the plot ( using the scale maps ) and renders them by QwtPainter::drawPolygon().

The more difficult thing about shape files is, when they represent huge data sets ( f.e all streets or all county borders of a country in high resolution ). For those you need some type of spatial index like a R-tree. Also the projection might be a too expensive operation for polygons of many points. So you should try to remove duplicates ( points mapped to the same screen position ) as soon as possible.

But if your shape files are small, the implementation should be no big deal.

Uwe

[swamyonline]

thanks Uwe,
that seems to be of huge labour for the application operating with big shapefiles. im also looking at QGIS implementation of shapefiles or other formats. actually, im trying to make a very simple map application (with Qt + Qwt) with zoom and panning facilities. thank u very much again. bye.