CAD programs

[Oceaneer99]

I've been looking into how you make a 3-view from a photograph of an airplane.  It is of course pretty complex, and involves finding the vanishing points of the image and all other sorts of perspective adjustment.

One program I am looking into right now is Google's free 3D software Sketchup.  I don't particularly have an interest in making a 3D electronic model (I'd much rather work in wood), but Sketchup does have a "match photo" mode that lets you put 2-point perspective axes onto the photo and then draw in that "space".  I'm still trying it out, but it looks like you could make a series of perspective rectangles along the length of the fuselage defining the height and width of the fuselage.  When you are done with this, you can rotate the resulting virtual image and look at the side or top view head-on, which would give you station points for drawing the fuselage.  My first attempt was a miserable failure because I got some reference point wrong.

I know that there are people in the group who have been able to use traditional graphical/drafting techniques to do this (conic projection), which is really amazing.  I have an article from WW I Aero that has a short discussion of the technique, but references another issue (that I don't have) with the full instructions.

I've seen examples of nice drawings that people have done with Sketchup.  I haven't tried it for a normal 2D drawing of airplane plans, as I usually use TurboCAD or a pencil for that.

I'll keep you posted if this work out.

Garet

[dave_t]

Garet, are you planning to draw something in particular? After being told that Sketchup was easy to learn I downloaded it and followed a few tutorials a while back, but didn't get very far. I guess I need to find a fifth-grader to teach me the basics. The kids do incredible stuff with 3D now. Well, so do we at SMM, just with chunks of wood.

[Oceaneer99]

I was trying to figure out the 3-view of the XCG-14 glider that you found a photograph of.  I did some more work tonight with Sketchup and tried to make rectangular cross-sections along the fuselage.  But it turns out the positions of the rectangles are ambiguous when you use the "match photo" option, and you can't rotate the image in 3D space until you are done.

However, you can use Sketchup to draw a box around, say, the side view.  If you can unskew that box in a graphics program, you would have the correct side view.  So far, I haven't made that work.

Garet

[RyanShort1]

Guys, there ARE some ways to draw well in Sketchup - and it is being used for woodworking and more. Here's a link to a blog with some interesting things: http://www.finewoodworking.com//blog/design-click-build
Also, here's some things I've worked on with with Sketchup for the Papermodelers forum: http://www.papermodelers.com/forum/design-threads/3343-playing-around-sketchup.html

Ryan

[Lotus-14]

The technique is called photogrammetry.

It originally was a graphical method used to create maps from aerial photographs.

It was also used to "map" physical objects, eventually being used during wartime as an intelligence tool to determine sizes and shapes of everything from buildings to aircraft.
It can be found now as a program which will build a multiview drawing from digital photos. You can find free programs on the net.
Years ago I had a friend who worked for Revell, and his job was to use photogrammetry to develop drawings of planes they were going to model.  He would go to airshows and take hundreds of photos of a plane, and use the information to develop his drawings.  This was before computers, so it was all done graphically.  You would be surprised at how accurate the drawings would be.

[Paul]

I once spent a winter doing photogrammetry for the Forest Service, that's probably why my glasses are as thick as they are now.