The product called ‘DTM’ indicates the height of the ground compared to the Belgian zero level (fictitious zero-D of Uccle). In other words, it is the orthometric height, commonly known as height.

The source data used to produce this DTM are the DTM at a 1m-resolution from the regions: data from Digitaal Vlaanderen (former AIV and former AGIV) for the Flemish Region, data from the SPW for the Walloon Region and data from Paradigm for the Region of Brussels-Capital. These regional DSM are derived from the clouds of points obtained during the LiDAR campaign (flight of 9 October 2021 for Brussels, from 19 February 2021 to 5 March 2022 for Wallonia and from 20 February 2013 to 20 April 2015 for Flanders).

As the Flemish and Brussels regional bodies deliver their products in Lambert 72, the NGI reprojected those in Lambert 2008 and achieved an interpolation in order to obtain a product with round coordinates, and then gathered them with the product of the Walloon Region (already in Lambert 2008) so that the newly created DTM covers the whole Belgian territory.

These source data are gathered and processed in order to obtain a homogeneous and regular grid with every meter a point in X and Y indicating the height of the ground level.

This grid makes the product DTM 1m, i.e. the DTM at a 1 meter-resolution.

This product comes directly from the regional data and is not updated.

The DTM 1m is resampled by bilinear interpolation in order to obtain the same type of grid at a 5m-resolution. This is also improved and updated in-house using direct photogrammetric surveys of points and structure lines based on the most recent aerial photographs in order to create the product DTM 5m.

The DTM 5m consists of a compilation of the best available data, and these are constantly updated and improved.

The product DTM 20m is obtained by resampling through bilinear interpolation of the DTM 1m in order to obtain a grid with a 20m-resolution. This lower resolution makes it a lighter product and allows it to be more widely distributed for all kinds of applications on a national or regional scale.

During the creation of DTM, the highest priority is to get a complete coverage.

The second priority is that the DTM represents the genuine ground level and no other surface (canopy roofs...).

These two priorities meet an important requirement for internal NGI applications and for most external customers.

Besides, the availability of DTM as a standard product (homogeneous and regular point grid) in a generic format (gdb raster file) that can be used by all the software packages is a remarkable asset for internal and external applications.