Maa-57.260 Fotogrammetrian erikoissovellutukset

Chapter 2: Classification of 3-D measuring tasks

TOPICS

• How to choose the reasonable solution for a 3-D measuring problem?
• Aspects to be considered while defining closer the measuring problem
• Activity of the object
• Task of the measurements
• Dimensions of the measurements
• Size of the object
• Measuring principles
• Number of object points to be measured
• Site for the recordings
• Processing site
• Requirements concerning the measuring accuracy
• The flow chart of deductions
• Examples of application classifications

How to choose the reasonable solution for a 3-D measuring problem?

 
• Basic criteria
• Don't forget that:
• First, the decision of using photogrammetry for solving a measuring problem should not be self-evident, although you should eagerly promote it with high priority.
• Second, you should consider thoroughly, at least for every new case, whether there would be any other alternatives to solve the problem in a more reasonable way.
• Third, after having made the right choice you hopefully include simulation for more detailed evaluation of the proposed prodedure.
• Some additional criteria for a reasonable choice
• Be aware of the performing capacity (accuracy, time consumption, costs, etc.) of the photogrammetric measurements in the case of measuring problem at hands. The knowledge about or the experiences upon earlier cases is most helpful. This can be supported by general simulations of some simplified network geometries already. In any new problem, where some new procedures or auxiliary devices should be developed or used, we often do underevaluate the time which will be needed for full execution including possible test measurements. This is usually the very critical part of considering, especially in the cases, where the clients are facing real and actual problems upon which their immediate actions depend, and they primarily want solutions, not always new photogrammetric developments.
• Remember, that with exiting things like photogrammetry, it is often easy to get the first job. But, if you cannot cope with the expectations which you promoted by your inspiring deductions, you will easily loose the client for one generation, or at least until the person you work with, will be retired or will leave the organization.
• Be aware of the realistic alternatives, which are available. It depends on the instrumentation you have, or maybe some colleague at any research organization, or in any consulting company has, and in Finland at least, whether there exists such instrumentation in the country or nearby.
• Be aware of the expected costs. Photogrammetry is a technique where one can measure on different kind of accuracy levels: low, moderate, high and even very high. We should consider which level is the reasonable one for the problem under discussion. The accuracy can be increased by increasing: the number of stations; images per station; the number of object points in the images; the image size or scale, and so forth. Here, finally, the simulation plays the decisive role even for experts. As the costs correlate with the amount of work expected for coping the accuracy requirements, we should really find out what is the real accuracy requirement of the client. This is a kind of procedural optimization problem, and should be solved by considering frankly all other alternatives as well.
• NOTE!
1. The deductions are not thriving to any exclusive choice of some measuring method.
2. The deductions are not developed until the very end in all cases, but can be done as well.
3. For some ends of deductions I have listed measuring examples in order to clarify the procedure.