Not accurate extent frame in map overview

[gislab]

If map overview is turned on and docked, the red extent frame is usually not accurate, i.e. either top/bottom bounds are missing until you start resizing.

Minor issue of course, but still.

Example: ​http://gis-lab.info/images/screenshots/20091205-kn6-11kb.jpg

[lutra]

Are you sure that are "missing"? It seems to me that if enlarge width/height of the overview box than the lines do show in the right place.

By the way, other overview issues are: #2181 #2166 #1449

[smizuno]

I believe the extent frame is operating correctly. The main intent of the frame is to show what area in the full map data is currently being displayed on the main map when zoomed in.

These are some factors that affect the display position of the rectangle:

1. Aspect ratio of the Overview vs. main map canvas.

2. the Overview shows the full extent exactly for all active layers (within its aspect ratio), but the zoom full extent actually puts a 5% additional buffer so the data are not right on the edge of the map. This will cause the rectangle to be outside the overview if both canvases have the same aspect ratio.

3. The small matter of + or - one pixel due to conversion of floating point values to integer.

A better test is to zoom in until the rectangle is the smallest size it can be, then positioning the rectangle over a feature on the map. That feature will be displayed on the main map.

[mayeulk]

wrong overview (using OSM data: monaco.osm)

[mayeulk]

In the example ​http://trac.osgeo.org/qgis/attachment/ticket/2243/wrong_overview.png, the overview is almost correct if I pan near the North of the areao of interest (Monaca). The more I go in the south, the more it is wrong. Having the pane docked or floating does not change anything.