Some time ago there was some discussion of modeling everything FWF and 3D
digitizers to accurately measure the complex dimensions of some of the
pieces that must go under the cowl. I vaguely remembered a process involving
photography to accomplish that end. That process involves taking a picture
or a series of pictures and then computing whichever coordinates you are
interested in. At that time I couldn't bring up the technical word. Today,
that word popped into my mind. It is photogrammetry.

Has anyone any information on the mathematics involved?

The motivation for all this is as follows. It seems to me that modeling the
bits and pieces that go under an aircraft cowl would be made much simpler if
we could simply take a series of pictures of the gadget to be modeled, feed
the resulting pictures to the computer and get accurate coordinates of the
said gadget, preferably in a machine readable form.

Doc Custer
Retired software engineer and sometime Audiologist Building RV9-A. Fuselage

You can do that in Rhino Doc. Under "View" move down to "Background Bitmap"
and select "Place". Choose a jpg as your back ground. You can then scale it
to the proper size knowing only one dimension. That is exactly what I did
here using the dimensions Mark sent me.

You then have to make the other measurements you are seeking manually.

Paul Lamar ...No rotor no motor.


Dr. Custer,

Photogrammetry is used to measure more than digitize.   We use it to align
large radio telescope surfaces.

We have a MetricVision MV-200 laser radar which can digitize.   This
technology is faster and more accurate than photogrammetry but not good for
outdoor applications.  We have digitized objects up to 60m on a side.

http://www.metris.com/products/laser_radar/laser_radar/

-Ben

Thanks Ben. Very Impressive. Probably out of my price range. :)

I was hoping that my posting would jog someone's memory and point us
to some references. I was hoping we could gin up a PC application that
would apply the appropriate transformations and give us reasonably
accurate results. The process would go something like this. Take a
photo of the subject with the necessary photogrammetry objects in it.
Feed the result to a visualization or modeling program. Select the
points of interest, pass these points to the transformation program
and get the transformed coordinates back. All of this is just hopeful
speculation. I know nothing of the complexities of photogrammetry.

One of the local land surveyors has a program with the ability to
input aerial photographs and produce accurate maps that meet legal
requirements. His program uses landmarks that have known coordinates
to derive the transformation coefficients necessary to produce
accurate maps from aerial photos. Maybe we can make use of his
programs. I will go talk to him about it.

The motivation for all this is to be able to model a FWF installation
with sufficient accuracy in order to:

1. determine the proper location for all the necessary gadgets that
need to fit under the cowl with no interferences,

2. design a cowl that will fit the first time,

3. calculate weight and balance so as to determine the proper
location for the engine, and

4. design a mount for the engine.
All this without the need for a FWF mockup.

Doc

We have accurate 3D Rhino models of many of the parts Doc.
Just let me know what you need.

Paul Lamar



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