Digital Surface Model (DSM)
The Digital Surface Model (DSM) represents terrain surface along with any objects and features protruding over it, such as buildings, trees, bridges, overpasses and other infrastructure. Poland maintains and updates the DSM based on a 0.5×0.5 m mesh for urban areas and on a 1.0×1.0 m mesh for the rest of the territory.
Figure 1. Digital Surface Model
At the moment, there are no services available for viewing the DSM. To obtain a DSM visualization, you have to prepare it on your own based on downloaded source data, e.g. in QGIS.
DSM downloading services
DDSM data is provided free of charge and can be used for any purpose. Data can be downloaded from www.geoportal.gov.pl, section "Data for download", layer group "Digital Surface Model". There are two layers in this group: "NMPT-PL-KRON86-NH" and "NMPT-PL-EVRF2007-NH".
Figure 2. Layers to download DSM data available at www.geoportal.gov.pl
When you enable one of the specified layers and zoom in on the area of interest, you will see rectangles which represent DSM data sections. Click the area of interest to display the option to download the relevant file, as shown in Fig. 3.
Figure 3. DSM data sheet downloading process
As a result, a file containing DSM data will be downloaded to your computer, and depending on your decision, displayed in a default application, as illustrated in Fig. 4.
Figure 4. Fragment of a DSM data file in Arc INFO GRID format
DSM data at www.geoportal.gov.pl are downloaded via WMS, depending on the elevation system:
Specifically, the GetFeatureInfo feature is used for this. It shares a link to download the relevant DSM file as an attribute in the clicked location. If you connect these services to QGIS or other software, you can use such software to download DSM data directly (Fig. 5).
Figure 5. DSM data sheet downloading process in QGIS
An alternative way to download DSM data is to avail yourself of WFS service (Fig. 6) used to present indexes of the Digital Surface Model (DSM) available in the National Geodetic and Cartographic Resources.
- The first one presents the DSM per particular years (from 2000 to 2019) in the PL-KRON86-NH elevation system in every available format.
- The other one presents the DSM per particular years (from 2018 to 2021) in the PL-EVRF2007-NH elevation system in every available format.
Figure 6. WFS for DSM depending on the elevation system
You can download DSM indexes using any software that supports a WFS client feature, such as QGIS. You can easily download each DSM sheet from the displayed sheet index. This operation is supported by the „Informacja o obiekcie” (About object) tool. When you click the selected sheet, it will display its metadata, including „Link do pobrania” (Link for download) that you can use to download DSM measurements.
Figure 7. Application of DSM-related WFS in QGIS
Another way to download DSM is to use WCS services whose URLs are published at www.geoportal.gov.pl:
Figure 8. For information about WCS services concerning DSM, see www.geoportal.gov.pl
The most convenient way to use WCS services is to connect them to QGIS as a data source, as shown in Fig. 9.
Figure 9. Application of DSM-related WCS in QGIS
When the layer is created in a QGIS project, the service generates a DSM image of the viewed area. Use the export option illustrated below to save a fragment of the DSM as a file.
Figure 10. Export of the DSM to GeoTIFF file
As a result, you get a local file consistent with the settings which represents the respective fragment of DSM raw data or rendered image. For technical reasons, in WCS, the area available for a single download is limited, but the service is suitable for downloading fragments corresponding to around a dozen original DSM sheets.
The DSM can be also downloaded via WCS directly from www.geoportal.gov.pl using the „Pobierz dane z usługi WCS” (Download data from the WCS service) tool. You can find this functionality on a toolbar in the left part of the map application user interface, as illustrated below.
Figure 11. Downloading DSM via WCS
To download data click the tool icon, select the data for download in the displayed pane, or select a spatial range on the map (max. 10 km2), as shown in Fig. 12.
Figure 12. Downloading DSM via WCS
Afterwards, all you have to do is download the prepared data file:
Figure 13. DSM file downloaded and uploaded to QGIS
The tool is particularly useful when the area of interest covers e.g. four sheets, and, if downloaded in the conventional manner, would yield four sheets that you would have to put together. By using the functionality provided, you can quickly download a ready-made fragment, no matter what the source data sheet arrangement is.