Datums coordinate systems and map projections 5 Coordinate

Datums, coordinate systems and map projections 5. Coordinate reference systems in GIS Lennert Schepers lennert. schepers@vliz. be Britt Lonneville britt. lonneville@vliz. be

GIS terminology • Different GIS systems (QGIS, Arc. GIS, …) use different CRS terminology • GIS software works with projects/data frames – A project/data frame has a CRS • Can contain different data layers with their own CRS – On-the-fly reprojection: • All the layers are automatically reprojected to the project/data frame CRS • In QGIS < 3. 0, you have to enable OTF reprojection – If a layer has coordinates, but no coordinate reference system: • • • Set layer CRS Raster: Assign projection Define projection Catalog → properties → edit spatial reference/coordinate system This will not change the coordinates, only the CRS!

GIS terminology II QGIS / Arc. GIS • To transform the layer from one CRS to another CRS: – – – Save as… > select CRS Raster: Warp (reproject) Vector: Project Raster This will transform the coordinates from one CRS to the other CRS • Georeferencing: – Assign a coordinate system to raster data by using the coordinates of control points • Scanned map/raster data without CRS • Control points on map with known coordinates (CRS? ) • Project raster to CRS of control points – Georeferencer / Georeferencing toolbar

Time for some action! GIS practical exercise: OTGA website