GSD-Elevation data, grid 50+ nh

Transcription

1 1(5) Date: Document version: Product description: GSD-Elevation data, grid 50+ nh

2 LANTMÄTERIET (5) Table of contents 1 General description Contents Geographic coverage Tiles Reference systems Description of quality Data capture and grid production Currency Quality Positional accuracy Metadata Data access and contents Format... 5

3 LANTMÄTERIET (5) 1 General description GSD-Elevation data, grid 50+ from the new national elevation model contains ground height values at the intersections of a 50 m grid. The product can be used for rough analysis and visualization. 1.1 Contents The product consists of height values with two decimals in a raster grid with a resolution of 50 metres. 1.2 Geographic coverage GSD-Elevation data, grid 50+ is nationwide. However, the production of the national elevation model is not yet complete but the grid will be completed as the productions continues. Production of the national elevation model can be followed at Lantmäteriets homepage. See under Höjddata. 1.3 Tiles The elevation data files are in index tiles of 100 x 100 m and they are divided according to Swedish counties. Some files extends over the county border, so if several counties are downloaded, those files will be included more than once. Index tiles of 100 x 100 km.

4 LANTMÄTERIET (5) 1.4 Reference systems In plane: SWEREF 99 TM In height: RH Description of quality For detailed information about data capture, production and quality of data used to produce the 50 m grid, see the document Quality Description of National Elevation Model, available at Data capture and grid production A national elevation model is produced during using airborne laser scanning. A grid with 1 m resolution is produced by linear interpolation in a TIN (Triangulated Irregular Network), constructed from laser points representing ground and water. Grid 50+ is based on this data set. A 5 m grid is interpolated from the 1 m grid, then 10 m from 5 m, 20 m from 10 m, and finally 50 m from 20 m. Bilinear interpolation is used for this interpolation. This chain of interpolations means that every height value is representative for a larger area than if the 50 m grid was produced by selecting heights directly from the 1 m grid. 2.2 Currency Frequency of updating is yet to decide. 2.3 Quality Positional accuracy Standard error in height in a moderate hilly landscape is about 1 m. The maximum error can however be many times larger. Errors increase in strongly hilly landscapes. The stepwise method of creating a more and more sparse grid has the effect that the landscape is smoothed: high peaks will be lower and deep valleys shallower. 2.4 Metadata A shape file with date of laser scanning can be downloaded from the ftp-site, stored in a separate folder (see below).

5 LANTMÄTERIET (5) 3 Data access and contents Data can be downloaded from a ftp-site under Open data on Lantmäteriet s homepage: The data folders are divided according to Swedish counties. There is also a folder with data for the whole country (as far as there are data). Metadata files will be found in a separate folder. This product description can be found at The file name consists of the coordinate of the lower left corner, indicated at 100 km. Example: nh_64_4.tif Below is an example of file names after being downloaded: 3.1 Format GSD-Elevation data, grid 50+ is available in GeoTiff format. More information about GeoTiff can be found at: Height values are represented by floating-point numbers and the files are compressed with Deflate. Height value represents the entire area of the pixel (50 x 50 m, PixelIsArea). The following tags are used for georeferencing and for defining no data values: ModelPixelScaleTag (33550) ModelTiepointTag (33922) GDAL_NODATA (42113)