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
- Click Add delimeted Text File. Select the input file GBdata\GBData\GNSS\Festpunkte_Forstbotanischer_Garten.csv. Define X field: East and Y field North. OK.
- 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.
- Activate Web --> Openlayers plugin --> Google Maps --> Google Satellite.
A high spatial resolution aerial othophoto originally aqcuired in 2009 provided by GeoBasis-DE/BKG (Bundesamt für KArtographie und Geodäsie, Frankfurt is loaded in the viewer. Note, the active CRS is automatically changed to EPSG:3857 (WGS84 / Pseudo Mercator).
- Add additional open data sets of the BKG. Click Add WMS Layer. Layers --> New. Fill the connection details. Name: WMS BKG, URL: http://sg.geodatenzentrum.de/wms_dtk250. Connect. Select Layer ID = 01, Name = dtk250. The topographic map 1.250.000 of Germany is loaded. Zoom out to a larger view extent.
Click Add WFS Layer and Server connections New. Fill the connection details. Name: WFS DLM250 BKG, URL: http://sg.geodatenzentrum.de/wms_dlm250. Connect. Mark the row with TITLE = OBJART_43002_f01 (Forest). Check Only request features overlapping the current view extent. Add. , Name = dlm250. The topographic map 1.250.000 of Germany is loaded.
