[Interest] Zooming with QGraphicsView/QGraphicsItem

Israel Brewster ijbrewster at alaska.edu
Wed Aug 7 20:01:09 CEST 2019


I have a QGraphicsScene/QGraphicsView that I am using to display a map (and some data). The map is in the mercator projection, with the x and y coordinates of the scene corresponding to map coordinates, so the background images are rather large. Images are loaded into a QGraphicsObject which is then added to the scene. The object types are defined by a third-party library, so I don’t have the option of using different objects, such as QGraphicsPixmapObject or something.

This works fine when I’m zoomed in to the map. Coastlines are nice and sharp, with no issues:


However, when I zoom out, the coastline becomes quite pixelated, and difficult to see in places:


How can I fix this? My first thought was to change the size of the background image so it could scale better, but that didn’t seem to help. In retrospect, this makes sense: at the end of the day, the background image has to be the correct size for the mercator projection, so while I can certainly change the pixel density, the overall size, and thus how much scaling is needed to display a given area, is fixed.

---
Israel Brewster
Software Engineer
Alaska Volcano Observatory 
Geophysical Institute - UAF 
2156 Koyukuk Drive 
Fairbanks AK 99775-7320
Work: 907-474-5172
cell:  907-328-9145

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