Wrong measurements when background is from a tiled service

[qgib]

Author Name: Paolo Cavallini (@pcav)
Original Redmine Issue: 12143
Affected QGIS version: 2.6.0
Redmine category:projection_support

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The scale gets wrong if one adds a tiled baselayer (e.g. Google or OSM via OpenLayers plugin, or via GDAL XML). E.g. at 1:2257 scale, on the video a 100 m line is 4.8 cm; adding a baselayer it becomes 6.9 cm, without changing the scale.
If I load a EPSG:3003 layer, add an OpenLayers plugin layer, the scale gets wrong and the project projection is set at 3857. Changing the projection back to 3003 makes things right again.
Apparently GDAL does not choose the correct zoom level to display the tiles. It does not seem related to the OL plugin, as it behaves the same on the server (seen through LizMap, with the same baselayer).

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• easy_fix was configured as 0
• regression was configured as 0

[qgib]

Author Name: Paolo Cavallini (@pcav)

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AFAICU this is related to EPSG:3857 being unsuitable for measurements.

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• resolution was changed from to invalid
• status_id was changed from Open to Closed
• description was changed from The scale gets wrong if one adds a tiled baselayer (e.g. Google or OSM via OpenLayers plugin, or via GDAL XML). E.g. at 1:2257 scale, on the video a 100 m line is 4.8 cm; adding a baselayer it becomes 6.9 cm, without changing the scale.
  If I load a EPSG:3003 layer, add an OpenLayers plugin layer, the scale gets wrong and the project projection is set at 3857. Changing the projection back to 3003 makes things right again.
  Apparently GDAL does not choose the correct zoom level to display the tiles. It does not seem related to the OL plugin, as it behaves the same on the server (seen through LizMap, with the same baselayer). to The scale gets wrong if one adds a tiled baselayer (e.g. Google or OSM via OpenLayers plugin, or via GDAL XML). E.g. at 1:2257 scale, on the video a 100 m line is 4.8 cm; adding a baselayer it becomes 6.9 cm, without changing the scale.
  If I load a EPSG:3003 layer, add an OpenLayers plugin layer, the scale gets wrong and the project projection is set at 3857. Changing the projection back to 3003 makes things right again.
  Apparently GDAL does not choose the correct zoom level to display the tiles. It does not seem related to the OL plugin, as it behaves the same on the server (seen through LizMap, with the same baselayer).