(Henrik Haggrén, 19.1.2001)
Chapter 2: Classification of 3-D measuring tasks
How to choose the reasonable solution for a 3-D measuring problem?
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
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
Third, after having made the right choice you hopefully include simulation
for more detailed evaluation of the proposed prodedure.
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.
The deductions are not thriving to any exclusive choice of some measuring
The deductions are not developed until the very end in all cases, but can
be done as well.
For some ends of deductions I have listed measuring examples in order to
clarify the procedure.