SCALGO Live Documentation

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Country Specific - Poland

Our elevation model of Poland is based primarily on the Digital Terrain Model (pl. Numeryczny Model Terenu) made available by the Head Office of Geodesy and Cartography (pl. GUGiK). We strive to keep our model up to date with the latest sources.

Elevation measurements in Poland generally use either the Kronsztadt 86 (PL-KRON86-NH) or European Vertical Reference Frame (PL-EVRF2007-NH) system. Since the elevation model from GUGiK is published in a mixture of PL-KRON86-NH and PL-EVRF2007-NH, SCALGO has applied a correction so that all data is in the same vertical reference system, namely PL-EVRF2007-NH.

In order to use an elevation model for hydrological analysis such as watershed and flow accumulation computations, two primary conditions need to be met:

  • The upstream area of any river should be covered by the elevation model.
  • Structures on top of the terrain should only be present in case they actually block water from flowing under or through them.

Below, we discuss how we process the model to fulfill these conditions as well as possible.

Extensions

In order to cover all of Poland including upstream areas of all rivers, we have extended the open LIDAR data from the government of Poland with the SRTM v3 1-arc-second DEM, which has a resolution of approximately 30 meter per pixel.

Bridges and underpasses

Major bridges have generally been removed from the model delivered by GUGiK, making most bigger rivers able to flow freely to the sea. However, for many smaller bridges and underpasses, additional "hydrological corrections" may be necessary. These can e.g. be made through workspaces in SCALGO Live.

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Major bridges have been removed from the model.

Apart from vegetation and major bridges, also buildings have been removed from the terrain model during construction. When computing water flow paths, more realistic results are generally obtained when the elevation model does include buildings so water can be simulated to flow around them. In SCALGO Live, we accomplish this by adding buildings back into the model using a dataset of building footprints, where we raise all grid cells covered by a building to a height 10 meters above the highest terrain point within the building footprint. This model is called "Terrain/Buildings" and is the basis for all nationwide hydrological computations.

The building footprints are taken from the BDOT10k LoD1 Buildings dataset.

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Flow paths routed around buildings.

Converting between vertical reference systems

In SCALGO Live, all elevation measurements are shown in the modern PL-EVRF2007-NH vertical reference system.

To convert from the older PL-KRON86-NH vertical reference system to PL-EVRF2007-NH, we have used a model of height differences published by GUGiK.

We have made the model of height differences available in SCALGO Live to make it possible to do conversions between the two systems as needed. To convert from PL-KRON86-NH to PL-EVRF2007-NH in a given location, use the Point Info tool to read the model difference at the location you are interested in. A measurement in PL-KRON86-NH generally gains between 13 cm and 21 cm when converted to PL-EVRF2007-NH.

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Example of location where the elevation in PL-EVRF2007-NH is 81.46 m, and the model difference is 19 cm, so that the equivalent value in PL-KRON86-NH would be 81.46 - 0.19 = 81.27 m.

Coastline

We have removed parts of the LIDAR model that are off the coast, as the data is generally unreliable. The coastline is taken from the BDOT10k "woda powierzchniowa" vector dataset.

Base map and aerial photography

The default map view when you go to SCALGO Live shows an overview map from Mapbox. The street names and place labels are sourced from OpenStreetMap. You also have the option of viewing Aerial photography provided by Mapbox.