Praca Dyplomowa - Photogrammetry and Remote Sensing - AGH

THEORETICAL BACKGROUND
photos are processed in a stereo mode – nowadays usually with 3D glasses connected to the
workstation – to see two photos at once in stereo view. These photos are usually used for
making Digital Elevation Model (DEM) and orthophotomaps.
2.2.2 Close – range photogrammetry
The camera is located close to the object, handheld or on a tripod. Usually this type of
photogrammetry work is non – topographic. It is used usually to model buildings, engineering
structures, vehicles, cultural heritage objects, etc.
To be able to describe an object in 3 dimensions there is a need to be at least two pictures of
the object taken in a proper way. At the beginning of photogrammetry pictures were analogue
and specific instruments were used to match pictures and use them for map making for
instance. Nowadays everything is computerized and there are plenty of cheap, commercial
digital cameras which may be used for this purpose. There are also available metric cameras,
very accurate, with certificates of calibration, made for geodetic measurements. Their
specification is that they have fixed settings like: principle distance, aperture, etc.
Knowing camera parameters and location of the cameras, which is computed during camera
orientation (interior, exterior, relative and absolute orientation – or in one block during bundle
adjustment), which is mainly to coordinate photos in the space, it is possible to compute 3D
point from triangle – rays intersection (using at least two photos). Figure 2.1 shows this
principle. As these parameters are known, rays may be recreated. After the identification of
common points on each image it is possible to gain the position of this point in 3D space,
which is the intersection of the recreated rays.
Figure 2.1 Photogrammetric principle of 3D measurement; example on convergent image
configuration (Luhmann et al., 2006)
Firstly, the object of interest should be examined, if it is big/small and, what kind of features
it contains, etc. In respect to shape of the object, the proper camera with lens (wider angle or
not) should be chosen. If applying lens with wider angle the image scale may be bigger and
more details may be captured. But, it may also lead to bigger error (distortion etc.) and more
photographs needed to cover the entire object.
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