D45 Data Modelling
Prepared by : Karl Soar, Machine Automation, Leica Geosystems AG +41 71 727 3010 firstname.lastname@example.org Introduction Leica Geosystems’ LMGS-S and LMGS-P 3D systems employ an open-standard format called D45 for surface modelling. The chosen coordinate system can be state-based, or any locallygenerated project coordinate system, but it is necessarythat both the site’s control network (reference points) and the D45 model files are in the same coordinate system. A D45 is somewhat similar to, say, a DXF ‘wiremesh’ 3D Digital Terrain (TIN) Model, but with one key difference: Surface elements are described as rectangles, not triangles. This ensures accurate position, height, cross-slope, long-slope and, most importantly, steering information,within each element of the terrain model. (See diagrams below). A D45 file contains only Point IDs, Eastings, Northings and Elevations of points relating to, for example, the four corners of a rectangular concrete slab (e.g. joint positions and elevations. Crossfall, mainfall, stationing/chainage etc., are not listed in the file itself, and are calculated ‘on-the-fly’ when the D45 file is loadedinto the system. The simplest way to visualise a D45 file is as a series of cross-sections, cut left-to-right, along an “alignment”, e.g. a runway centreline, road centreline etc. Cross-sections must always be generated left-to-right (with respect to the ‘ design direction ’ of the alignment. Typically the designer might extract the cross-section points working left-to-right, in an ‘Up Chainage’direction.
The D45 internal file format is plain space- or tab-delimited ASCII, so allowing virtually any CAD system to be configured to output in D45 directly, or failing that, output as cross-section reports and re-formatted as a D45 via any ASCII text editor or Excel spreadsheet. To minimise the amount of D45 data that needs to be generated from your CAD system, consider the following : •Data only needs to be generated for ‘change points’ or ‘breakpoints’ , i.e. where changes in crossfall, mainfall or direction are required to be constructed. A ‘constant’ design, e.g. a rectangular car park with, say, a constant cross-slope would therefore require only 4 points, and could be ‘designed’ in Excel. A complex road alignment might require cross-sections to be cut at, say 1m, 2.5m, 5mor 10m intervals; you may need to consult your CAD system vendor to obtain information on
how to generate customised cross-section reports with the point data in the necessary order. Alternatively, consider using Liscad (sold through Leica) or Leica Site Manager, an AutoCAD-based CAD system, both capable of generating D45 format outputs natively. • Remember that the siteengineer (or machine operator) can choose the desired vertical offset from the model ‘on-the-fly’, so where construction design permits, consider generating simply a ‘finished surface’ model, from which, for example, a grader or dozer operator could place and fine-trim subbase materials at a constant vertical offset below FRL (e.g. -275mm).
DXF Format Digital Terrain Model (TIN) vs D45 Format •Ideal for earthworks, bad for paving! Commonly referred to as a TIN (Triangular Irregular Network). Elements are typically triangular, described by the Easting, Northing and Height of each vertex to form a closed 3DFACE element type, with their order within the file not important.
This format is supported by Leica’s DTM Stakeout application (Article Numbers : 664410 for TPS1000, 667333for TPS1100) and is ideal for making as-built checks for Machine Automation systems.
Leica D45 Format Digital Terrain Model The same two-lane road in D45 would look like this:
Point numbers are listed in a fixed order, always left-to-right, in cross-sections at desired intervals, with respect to a design direction (in the case of roads/rail, often the centre-line in the direction of...