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home    |    Machine Geometry Applications      Photogrammetry

Application

Using ProGeo 3D

For 20 years it has been Status Pro’s central goal to make equipment which can be used by machine builders on-site. Typically our customers have a multi- tude of responsibilities on-site and “measurement” is just one of these functions. Therefore we strive to keep it simple. How many reference points are required and where to place them requires some training and experience.

However if the measurement-object remains similar in shape and form this can be learned quickly. Taking the photos is quite straight forward and this is supported by the software. The question is always “Was that suf- ficient?”.

Having taken the photos we automatically end up with a cloud of points. What happens next depends on what information we require from these measured points. Measuring surfaces is usually very straight forward and a report can be generated immediately.

The Point Monitor software supports the measurement of much more complex application. We can group points together and make best fit geometrical forms. We can call up the characteristics of these forms.

We can also compare the nmeasured forms with CAD diagrams. Point monitor is a very versatile geoetriuc package which is available in 3 steps.

Software Point Monitor – vollautomatische Auswertung

Software Point Monitor

Basic functionality:

  • Fully automatic point cloud analysis and reporting is possible.
  • DIY Analysis is fully supported.
  • Export of pointcloud in most current fiormats.
  • Practically unlimited projet size 64bit-Technologiesupported
  • Standard- und extened calibration models• Point quality monitoring
  • On the job and integrated calibration
  • System specified according to VDI 2634

Geometrical functionality

  • Flexible co-ordinate system definition
  • Best fit surfaces, circles, cylinders, lines etc
  • Characteristics of geometrical forms and there orientation in the point cloud.
    For example. Cylinder axis projection w.r.t center of circle.
  • Automatic recognition of Point adapters, bores, sharp edges corners and many other characteristics.

The Issue of Accuracy

The guide lines VDI 2634 is currently the best help we have in the search for a universally agreed definition of procedures and criteria with which the accuracy of photogrammetric systems should be judged.

The VDI 2634 defines a cube containing 7 reference rods. As illustrated in Fig 1. This cube has the dimensions 2 m x 2 m x 1.5 m. Each Reference Rod has 4 or 5 referenced points. The distance separating the points should be known an “contstant” with a precision above and beyond that achievable by photometric methods (ideally within a few Microns).

At the end of the day:
The accuracy of a photogrammetric system is then defined by the accuracy with which the systems locate these reference points in this reference cube. Typically the results are presented as deviations (Y Axis) with reference to the reference length as depicted in Fig 2.

In fact the achievable accuracy for any given application of this technology is dependent on a great deal of details.

For example: The object form, the camera’s resolution. The camera’s optical mechanical und thermal stability. The number of photos taken, the orientation of the photos. The position and accuracy of the reference rods.
Etc etc ...

In particular the visibility of the points from various incident angles can have significant influence on the achievable accuracy for a specific measurement.

For those who want to know more we recommend reading "Informationen zur Genauigkeit von photogrammetrischen Systemen“ you will find at Luhman, page 111 (http://dgk.badw.de/fileadmin/docs/c-645).

It is worth remembering that the size and accessibility of the object to be photographed has a significant impact on the achievable accuracy. Therefore when measuring large objects it is often using to introduce a few points of know position into the image. These reference socalled external reference points can be measured using alternative technologies.

Kalbrierwürfel
Fig. 1: Certified "Calibration cube"
Fig. 2: Evaluation of the measurements done with
the ProGeo 3D 30 System related to the VDI 2634
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