Unit 15 - Data reprojection

In this unit EU-DEM global dataset provided by Copernicus programme will be used. Jena region is covered by tile E40N30. Be aware that EU-DEM tiles covers large regions (4GB per tile).

Important

Note that a new Copernicus DEM product is available from Copernicus Data Space Ecosystem.

The DEM tile can be imported and automatically reprojected into the target project (jena-region) similarly as other input data used in this course. However, it is unnecessary to import the entire DEM tile into GRASS; only the portion covering the area of interest (AOI) is required. By using the -r flag of the r.in.gdal tool, it is possible to import only a subregion corresponding to the AOI. Unfortunately, the r.import module does not provide this option. For this reason, the data are reprojected manually. The input data are first imported into a new project (ETRS89-extended / LAEA Europe, EPSG:3035) and subsequently reprojected into the target jena-region (WGS 84 / UTM zone 32N, EPSG:32632).

Note

In order to save disk space the original EU-DEM tile was clipped by larger region than Jena AOI. Modified tile is available from eu-dem directory.

Create project for data import

EU-DEM dataset is provided in ETRS89-extended / LAEA Europe (EPSG:3035). Create a new GRASS project jena-eu-dem based on input eu-dem/dem_sample.tif file as described in Unit 02) or from EPSG code.

Important

Skip data import provided by project wizard since only subregion defined by Jena city region is planned to be imported.

Enter new project (PERMANENT mapset) and copy (ie. reproject) jena_boundary into the current project.

../_images/data-reproject.png
../_images/data-reproject-1.png

Fig. 82 Copy jena_boundary vector map from jena-region project (EPSG:32632) to the current project (EPSG:3035).

../_images/data-reproject-dialog.png

Fig. 83 Reprojection and default maximum segment must be confirmed.

Note

The same operation can be done by v.proj:

v.proj project=jena-region mapset=PERMANENT input=jena_boundary

Before importing DEM set computation region extent based on reprojected Jena city region.

../_images/region-extent.png

Fig. 84 Set computational region extent based on Jena city region.

Launch r.in.gdal (File ‣ Import raster data ‣ Import of common raster formats) to import DEM tile, don’t forget to enable -r flag.

r.in.gdal -r input=geodata/eu-dem/dem_sample.tif output=dem
../_images/dem-imported.png

Fig. 85 Imported DEM limited to current region extent. Visualized using elevation color table.

Reproject DEM into target project

Now switch back to jena-region (target) project (PERMANENT mapset).

../_images/switch-project.png

Fig. 86 Switch to jena-region project and PERMANENT mapset from Data tab.

Reproject DEM from jena-eu-dem project by copying in Data tab. Set desired resolution (25m) and choose appropriate resampling method (in our case bilinear).

Note

If a mask is enabled, it’s good idea to remove it before importing.

../_images/data-reproject-raster.png

Fig. 87 Reproject raster data by specifying target resolution and resampling method.

Note

The same operation can be done by r.proj:

r.proj project=jena-eu-dem mapset=PERMANENT input=dem method=bilinear resolution=25
../_images/dem-3d.png

Fig. 88 Imported DEM in 3D view. Jena city region by blue color.