by Frank BOOCHS, Anja GEHRHOFF, Markus NEIFER
i3mainz, Institute for Spatial Information and Surveying Technology
FH Mainz, University of Applied Sciences
Holzstrasse 36, D-55116 Mainz, Germany
A precise and true geometrical description of the objects of interest is a fundamental base of most applications and is a must in the field of CAD. Such a geometry is in general expressed by a large number of individual points placed on the geo-object in consideration. The total quantity of these object points is called digital object model and is generated by a data collection process. Several different techniques are known for the collection of points and a very common one is the use of metric stereo images. Then special equipment like stereo plotters have to be used. The technology of such instruments has been developed permanently and has led to very productive and flexible computer assisted plotting systems. Recently, the big technological step to pure digital systems has been undertaken. However, the need of having the image information digitally available is a very demanding constraint for digital plotting systems. In many geo-applications images with a size of 23 by 23 cm 2 have to be used, what results in very huge data sets. Therefore most digital plotting systems have special hard- and software components for the handling and display of such large images.
The lack of these systems is, that they are very expensive and that their software depends on the hardware used. This hardware is very special, why the customer may not use his own one and the producer additionally has to invest great effort to keep track with his software to the progress in hardware technology. In parallel a great technological progress can be observed in the field of 3D applications, which is driven by the market of 3D animated and graphic oriented computer games. This market is dominated by PC systems, which are well equipped giving the power needed for multimedia applications. Furthermore companies like Elsa, Diamond or Evans & Sutherland offer high end graphic boards providing refresh rates up to 230 Hz per frame, true colour, special chips optimised for graphics and the opportunity to use stereo images. Some of the boards come already with connectors compatible to the VESA standard for the use of stereo glasses. Such boards are very useful for stereo systems, because there is no further need for special controllers, they are already onboard and the customer only needs to connect to an appropriate viewing system. This may consist of LCD glasses and a high quality monitor. All these parts together form a powerful platform for stereo applications at a moderate price.
Looking at the potential of these PC-systems it is of interest to have the possibility to use them for stereo measuring process. This can be achieved with software designed under the aspects of photogrammetry but without any constraints coming from an adoption to special hardware features. This guarantees portability and the advantage to use the software on different platforms. With respect to CAD applications this software needs to have an interface to standard program packages like AUTOCAD, for example, allowing to use the whole functionality of such data collection and construction tools. The generation of such an interface is simplified, if an object-oriented programming technique is chosen. This makes it possible to build individual interfaces for different CAD packages and provides a high degree of flexibility. Furthermore it makes it easier to build complex software packages and speeds up the process of development.
The object-oriented approach is also supported from the side of graphical interfaces, and various solutions are offered. Comparing MFC, Troll Tech’s Qt and the free wxWindows the latter one seems an optimal choice, because it supports most of the common platforms (Windows, Unix, Linux, OS/2 with modifications), is free available and has a very good assistance with mailing lists. Taking all these considerations in account, we propose a solution for a stereo system, which is based on standard graphic software tools, has an object-oriented design of the application software and is realised on a powerful PC-hardware configuration. The design of soft- and hardware and the integration into the CAD world will be presented and first results with the prototype will be shown.