We have some 100+ georeferenced raster's in ecw format. All the rasters are in EPSG:20935 (Arc 1950/UTM 35S) reference system. We have captured the data_footprint of those rasters in the same CRS. But, if the scale level is say 60,000 or 40,000 QGIS is showing a shift between the data_footprint polygon and the respective raster. Once i change the scale to 20,000 or 10,000 the polygon and the raster boundary matches perfectly. Could anyone explain why this happens ?