Laser-Scan Ltd.

Software Product Specification


Issue 4.0 8-May-1992
Copyright (C) $$year Laser-Scan Ltd
Science Park, Milton Road, Cambridge, England CB4 4FY  tel: (0223) 420414
Document "DTMPREPARE SPS"                               Category "SALES - Spec"
Document Issue 1.0   Tim Hartnall                       14-Jan-1987
  Issue 1.1   Tim Hartnall                       25-Jun-1987
  Issue 1.2   Tim Hartnall                       21-Oct-1987
  Issue 2.0   Tim Hartnall                       20-Jan-1988
  Issue 3.0   Dave Catlow                        10-Jun-1988
  Issue 4.0   Jon Barber                         08-May-1992



DTMPREPARE is an advanced data preparation package for vector data which is to be used for DTM generation. It is recommended for use with the Laser-Scan "DTMCREATE" DTM creation package.

The DTMPREPARE package is one of 3 Laser-Scan DTM production and manipulation packages:

All three packages are supplied with a background package "MATRIX". Package MATRIX contains Laser-Scan DTI (*Digital *Terrain *Image) format DTM management programs, a basic DTM viewing program and a DTI manipulation subroutine library for applications programmers. (See separate SPS for MATRIX package)

DTMPREPARE - input/output

Data input to the DTMPREPARE package is from Laser-Scan IFF (*Internal *Feature *Format) vector files. Input vector data may consist of contour strings and/or spot heights, and two dimensional river and ridgeline strings. Modules within DTMPREPARE enable the user to select automatic contour data validation options, and options to derive three dimensional river and ridgeline strings from two dimensional input by reference to relevant contours. Data output is in IFF format.


DTMPREPARE offers the following features:


The following computer hardware requirements are needed to run DTMPREPARE.


DTMPREPARE modules run under VAX VMS Version 5.4-3 (or later version, assuming continued upward compatibility by DEC), concurrently with other interactive and batch processes.

A minimum working set of 4000 pages is recommended.

Laser-Scan's *IFF *Map *Processing package (IMP) is essential. Laser-Scan STRUCTURE package is a prerequisite for the module I3D. Laser-Scan's LITES2 interactive digitising and editing software is recommended for digitising and editing vector input data. LASERTRAK automated digitising is recommended for large numbers of input documents.


The minimum hardware and software requirements for any future version of this product may be different from the minimum hardware requirements for the current version.


DTMPREPARE is a fully supported Laser-Scan standard software product.


DTMPREPARE consists of the following component modules:


The module I3D is a 3D string generator. Its purpose is to generate heighted river or ridgeline 3D strings by overlaying unheighted strings with contour data.

The 3D strings output by I3D may be input to the Laser-Scan DTMCREATE package as rivers, ridgelines or 3D breaklines to control valley floors, hill tops and complex geomorphic areas disturbed by mining or other human activity.

The module must be used in conjunction with the STRUCTURE package module ILINK, and the LITES2 interactive cartographic editor.

ILINK is used to ensure that the unheighted river and ridgeline data has exact junctions suitable for link-node structuring within I3D. In the case of river strings, the link-node data structure is used to derive network relationships to enable accurate heighting of river confluences and to ensure consistent down hill flow.

The LITES2 cartographic editor is used to generate supplementary heighted features for areas of the map where the contour information alone provides insufficient control. I3D produces a LITES2 guidance file that will allow the creation of supplementary features to be automatically driven.

I3D offers the following features:


The module ITCHECK detects and tabulates errors in IFF vector data. It is used to validate a height value associated with a map feature, and to check for errors in the form of a feature.

Typically, the data input for checking will consist of heighted contours and spot heights, and map features such as rivers and ridge lines. These features are used in the generation of a DTM by modules in the package DTMCREATE.

Errors in height or form may arise from data capture or data editing operations. Validating the map data using ITCHECK is an important aid to controlling the quality and accuracy of the output DTM, and in a production situation may avoid expensive and time-consuming problems resulting from the input into the terrain modelling process of incorrectly heighted or malformed data.

Features found in error are reported in a text file and may be optionally copied to a separate IFF file for subsequent plotting or interrogation. Optionally also a LITES2 guidance file may be produced to assist correction or investigation of the features that have been detected in error.

The checks performed by ITCHECK are grouped into six categories. A single category or a number of categories of checks, may be selected at run time. The following checks are performed in each category:

Category 1 Height checks

Category 2 Link checks

Category 3 Intersection checks

Category 4 Profile height checks

Category 5 Loop, duplicate points and spot height single coordinate checks.

Category 6 Validity of spot heights checks

The user may select which group of features are input into the checks. For example, checking may be restricted to just index contours. Feature codes are used to define which features belong to a given group.

All parameters controlling the check operations may be defined by the user at run time.