The Laser-Scan DTM software packages provide tools for the production, validation, manipulation and viewing of matrix data, particularly of elevation (height) data. The DTMCREATE package consists of four interlocking software modules for the generation of DTM data from Laser-Scan IFF (Internal Feature Format) vector data.
In most cases the output matrix, or DTM, will be derived from contour, 3D river, 3D ridgeline and spot height information. Other forms of input data can be handled. For instance, 2D seismic line information, random borehole or oil well data. Laser-Scan DTMCREATE software represents an attempt to provide a single mapping system that copes well with all these types.
It is however optimised and extensively used for grid terrain model generation.
Incoming string data usually consists of digitised x,y data locations, each with an associated z or height value. An alternative for isarithmic data are strings of x,y locations with a single implied surface value. Single point (spot height) data can also be used.
Data entering the system may contain information about surface characteristics other then height, as well as defining the location of particular values. The usual case is either implied or specified detail concerning the local slope at the data point. This could be of various types:
All three types are still represented by location and value, but in addition every string must also possess a type identifier corresponding to the classes above.
In addition to data type, individual data points may also be flagged to represent the following geomorphological attributes:
The Laser-Scan DTM creation software uses such data coded with height, type and geomorphological flag attributes to produce a TIN (Triangular Irregular Network). An interactive graphical editor is provided to enable the user to alter and refine the triangulation.
The triangulation is then used to generate a rectangular grid spaced at some geographical interval over the area concerned. It is not possible in such a grid - unless it is very fine - to ensure that the data values themselves are represented at the grid nodes, but the general convenience of using the very simple structure of direct row storage makes grid manipulation and automated comparison of one grid with another quite straightforward.
The blend of triangulation and grid based methods provided by the Laser-Scan DTM software offers economy of execution speed and convenience of use. Once calculated and stored, further editing and revision of a triangular digital terrain model (DTM) can occur at any time. It is a simple process to output a grid DTM based on the triangular structure at the resolution required by the user. The same triangular DTM can then be used, without further calculation, to generate as many rectangular grids as required from all or part of the data area.
This manual attempts to explain the philosophy of the DTMCREATE triangulation approach to DTM production, together with a module by module reference guide to the package.