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.

A full overview of when the LIDAR elevation data in Poland was acquired is available by clicking the gear icon next to an elevation layer, selecting the "Source" tab, and "Show source information".

Bridges, underpasses and hydrological corrections

Major bridges have generally been removed from the model, but for many smaller bridges and underpasses, additional hydrological corrections that allow water to flow through such structures may be necessary. Scalgo Live Poland includes a nationwide hydrological correction set based on layers from the GUGiK BDOT10k dataset. Corrections have been generated at locations where rivers intersect roads or railroads, as well as at river sections that overlap with culverts (przepust). Secondly, corrections have been generated at road overpasses and tunnels. Each correction thus follows a line in the BDOT10k river or road network, with end points adjusted to match the elevation model as well as possible. In places where the elevation model is already hydrologically corrected (e.g. at large bridges), corrections are not generated.

This data set is machine-generated, so some errors should be expected. However, since we only include corrections along known river and road lines, we believe it to be conservative in terms of water flow.

The set of corrections is available under the Hydrological Corrections category in the Library.

The national analyses use these corrections, and workspaces created using the predefined "Flash Flood Map" or "Sea-Level Rise" buttons also include them by default. If you create a workspace through any other means than the predefined buttons (e.g. if you upload your own model), you can include corrections in that workspace through the workspace Actions tab by clicking Import corrections, they will not be included automatically.

Buildings

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 Buildings dataset.

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.

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.

Land cover

The Scalgo land cover map is available in Poland. For more information, please consult the land cover section of this documentation.

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 an aerial photography map in standard resolution for the whole country, or a high-resolution aerial map covering part of the country, provided by GUGiK WMTS servers.