Measurement camera
The measuring image camera (or measuring chamber ) is a camera with minor imaging errors or with errors that can be precisely determined by calibration and thus corrected later in the post-processing of the images.
Areas of application
It is mainly used in photogrammetry and remote sensing to
- to reconstruct the shape of objects - e.g. B. for medicine , archeology or monument protection
- Measure architectural facades , buildings or quarries and determine the coordinates of their most important points
- Taking series of photos from the aircraft and using them later in geodesy or cartography to produce maps .
- In the space Details of the planet to measure .
Types
Analog measurement image camera
For analog (= film-based) measuring image cameras, formats of 23 cm and the frame marks that are exposed on each image of the film are typical . They help to determine the internal orientation of the camera (main point of the image and focal length ). The latter is between 8 and 60 cm, depending on the lens, and is calculated or calibrated to 0.001 mm each time because it depends, among other things, on the temperature and air pressure. The evaluation takes place with special evaluation devices , about the size of a desk, which allow accuracies of 0.002 to 0.01 mm in the image scale.
With terrestrial be measured control points is exterior orientation produced. This means the parameters of the location (coordinates x, y, z) and the recording direction (angle of rotation ω, φ, κ) for the transformation of the image coordinates into the national coordinate system (e.g. in Germany and Austria: Gauß-Krüger coordinates ) .
Digital measurement image camera
With digital cameras becoming a place photographic film or more CCD sensors used. A standard analog film for aerial cameras has a negative size of 23 cm × 23 cm with a film length of up to 152 m. Digital sensors of this size are currently not feasible. Therefore, several sensors are often used, which are added together to form a large image. For example, cameras from Intergraph Z / I Imaging (DMC) and Microsoft / Vexcel (UltraCam) use this technology. In contrast, there is still the approach with line sensors, for example from Jena-Optronik (JAS) or Leica Geosystems (ADS40). This makes it possible to achieve almost the same image coverage as with analog cameras with smaller sensors. The measurement accuracy of the digital aerial cameras is somewhat better.
The advantages of digital aerial photography are:
- significantly less noise than with scanned negatives
- Savings in film and development costs
- Better graded exposure areas
- Partly multi-spectral recordings possible ( e.g. infrared images and color images simultaneously)
- Faster further processing
- Thanks to the use of inertial navigation systems , both the internal and external orientation of the image data can be determined with much less effort. Position accuracies of less than 5 cm can be achieved even without control points .
A disadvantage is that correspondingly powerful computers are required, which are still not very common, especially in developing and emerging countries (raw data volumes of several dozen gigabytes per flight hour are not uncommon). The new technology is also associated with high investments. In addition, the manufacturing processes must be changed and the employees familiarized with the new technology. Analog chambers are no longer produced today (2007).
Manufacturer
The best-known manufacturers of measurement cameras are Leica Geosystems (formerly Wild and Kern, together with the Intergraph camera division , formerly Z / I Imaging, which is now also part of the parent company Hexagon AB ), Jena-Optronik GmbH (formerly Carl Zeiss Jena combine ), Carl Zeiss , Vexcel-Imaging GmbH (formerly Microsoft Vexcel Imaging) and Kodak . Another manufacturer with high-precision cameras in this segment is ALPA (ALPA Capaul & Weber AG) from Switzerland.