Exercise: Measuring point coordinates using WMS Google maps

Coordinates are often needed for ground control points (GCP) with the objective to georeference remote sensing data or scanned maps without graticule. Google maps can be used as one source for registering point coordinates.

Import highly accurate DGPS points stored in a ASCII CSV file

1. Click Add delimeted Text File. Select the input file GBData\GNSS\Festpunkte_Forstbotanischer_Garten.csv. Define X field: East and Y field North. OK.
2. Specify the coordinate reference system (CRS) ETRS / UTM zone 32N. Search for the EPSG code: 25832. Three precise geodetic survey points are loaded into the viewer. The current active project CRS is displayed on the lower left frame of the viewer as EPSG:25832.
3. Activate Web --> Openlayers plugin --> Google Maps --> Google Satellite. A high spatial resolution aerial othophoto originally aqcuired in 2009 by GeoBasis-DE/BKG (Bundesamt für Kartographie und Geodäsie, Frankfurt and provided as web map service (WMS) by Google is displayed in the viewer. Note, the active CRS is automatically changed to EPSG:3857 (WGS84 / Pseudo Mercator).