Have you noticed this in the measure tool info box part?: - if OTF is off:
The calculations are based on: Project CRS transformation is turned off. Distance is calculated in degrees, based on project CRS (WGS84). Ellipsoidal calculation is not possible with CRS transformation disabled. Distance is roughly converted to degrees by using scale at equator (1 degree = 111319.49 meters). - if OTF is on: The calculations are based on: Project CRS transformation is turned on and ellipsoidal calculation is selected. The coordinates are transformed to the chosen ellipsoid (WGS84), and the distance is calculated in meters. Moreover the User Guide (paragraph 8.8) is more clear: QGIS provides four means of measuring geometries: • the interactive measurement tools , • measuring in the Field Calculator, • derived measures in the Identify Features tool, • and a vector analysis tool: Vector→Geometry Tools→Export/Add Geometry Columns Measuring works within projected coordinate systems (e.g., UTM) and unprojected data. The first three measuring tools behave equally to global project settings: • If “on the fly” CRS transformation (see Define On The Fly (OTF) CRS Transformation) is enabled, the default measurement metric is - different from most other GIS - ellipsoidal, using the ellipsoid defined in File → Project properties → General. This is true both when geographic and projected coordinate systems are defined for the project. • If you want to calculate the projected / planimetric area or distance using cartesian maths, the measurement ellipsoid has to be set to “None / Planimetric” (File → Project properties → CRS). However, with a geographic (= unprojected) CRS defined for the data and project, area and distance measurement will be ellipsoidal. • If “on the fly” CRS transformation is disabled, the measurement metric is planimetric when the project coordinate system is projected and ellipsoidal when the project coordinate system is unprojected / geographic. However, neither the identify tool nor the field calculator will transform your data to the project CRS before measuring. If you want to achieve this, you have to use the vector analysis tool: Vector → Geometry Tools →Export/Add Geometry Columns. Here, measurement is by default planimetric except if you choose the ellipsoidal measure. ----- Andrea Giudiceandrea -- Sent from: http://osgeo-org.1560.x6.nabble.com/QGIS-Developer-f4099106.html _______________________________________________ QGIS-Developer mailing list [email protected] List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
