The toposcope

During the fieldwork photos or video images are taken in a controlled way with a toposcope. This instrument also allows to perform the measurements necessary to link the images accurately to the 2D map used. After the calibration it becomes very easy to measure in the images. Photos, map and database form one interactive 3D system.The standard toposcope is an automatic level with an angle measuring device and a camera attached to it by means of an adapter.The adapter only allows rotations in 2 directions. You can switch between portrait and landscape view and can make a combination of a horizontal and an upward (or downward) photo. Many common analog or digital cameras can be used. However the camera should not have clear distortions of the lens. Lines that are straight in reality should also appear straight in the image. The camera does not have to be lined up with the lens of the automatic level, nor do you need to know in advance the viewing cone. You can even freely zoom in and out.
The toposcopic software consists of a fieldwork program (Topo.exe) and a photogrammetry and visualization program (Scope.exe). The combination Toposcope-Topo can be used to make inventories. The toposcope is very well suited to determine ground heights. To avoid making duplicate measurements an import routine has been written that can read 3D points. In such a case or if there is already an accurate map available with ground heights written on, the toposcope is primarily used as a solid camera-stand.
A the moment we are investigating if we may use a camera with GPS instead of the toposcope as described above. The determination of the camera position may not be accurate enough, but this may be corrected by recalculating the camera position in Scope. This can be done by correlating 3 points in the map to the corresponding points in the photo.
When accuracy is not very important one can also take the photos using a regular tripod. One should take care that the camera is not rotated around the horizontal axis. Furthermore one has to measure the height of the camera in relation to the ground surface. The camera position can be calculated as described above.  This method works well in build-up areas when you have a reliable digital map with some elevation data. However we do not recommend this method when you want to make a large 3D model using many photos taken in different directions.

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