by Tommy H. Thomason

Monday, December 10, 2012

Are You Going to Believe Me or Your Lying Eyes?

I've tried to make three-view drawings from photographs and failed. Photography experts can tell you why; all I want to do is illustrate the pitfalls.

This is an example of a pretty-good drawing compared to a pretty-good picture, which means it was taken from the side at pretty much a right angle. (Hopefully, the height versus width of the picture, which I took off the interweb as-is, wasn't changed in the process of getting it out of the camera and onto the web.)

What I did was match the tip of the radome and the bottom aft edge of the rudder of the picture with the outline drawing (traced very closely on Illustrator from a McDonnell lines drawing that might not be "exact" in shape but should be very close in terms of the locations of significant features like the position of the wing leading edge versus the tip of the radome and the trailing edge of the rudder).

Note that details on the forward fuselage in the picture shift aft including the location of the wing leading edge. The fuselage appears to be deeper in the photo with the length matched to the drawing but that sort of makes sense to me and can be corrected for to some extent by increasing the length to height ratio of the picture in the middle but keeping it the same at the right side. (Otherwise the vertical fin would not be tall enough.) Note that this slightly affects the angles of non-vertical and non-horizontal lines.

Another problem not illustrated above is that objects closer to the camera appear bigger than they really are with respect to those farther away, the difference being dependent on the camera lens used and the distance from the subject.

These effects are minimized but not eliminated by taking a picture from far, far away using a telephoto lenses.

The good news is that you can rely on the shape and relationship of small areas that are the same distance from the camera. For example, whereas the inlet ramp is way out of position in the full side view as shown above, if you zoom in on just it and resize the picture slightly, the ramp matches the pretty-good drawing very closely. Another trick is to locate something with respect to the centerline of the airplane that is way off to one side of the picture like the tips of the stabilators by drawing a line between them and finding its midpoint. Of course, that means that both the left and right side of the something in question has to be visible.

My conclusion is that you can refine a pretty-good drawing with the judicious use of pictures but you have to start with a pretty-good drawing in the first place or be able to make measurements of the key features of the subject, which is not as easy as it sound, also speaking from experience...

1 comment:

  1. You can also use trigonometry to correct the apparent shortening of the aircraft caused by the airplane's angle to the focal plane of the camera. Notice how the right landing gear appears to be forward of the left. This apparent distance on the photograph can be used to determine this angle, and the angle can then be used to calculate the correct length of the fuselage. The photo can then be stretched in Photoshop by the correct amount and location of key features determined from this stretched photo.

    This process takes more math than is practical to explain here, but it's not hard.