Topic Title

Does anybody have a method (three radius, maybe?) to construct
an approximation of a parabolic arch? I'm talking about the
arches that appear commonly in Spanish style architecture in
the Western US. I'm checking somebody else's work and they've
drawn one incorrectly. Graphic Standards, Google and Wikipedia
have been little help. A portion of an ellipse isn't close
enough. TIA

Hi Steve:

Check out this page:

http://www.sciences.univ-nantes.fr/physique/perso/gtulloue/conics/drawing/para_string.html

A series of radii -- increase one by the same amount as you decrease the other...

[Edit: look at the animation. At any given point, the one radius is from the top of the right triangle, down it's side, and the other is from the fixed point.]

Here's another:

http://www.punahou.edu/acad/sanders/geometrypages/GP19Parabola.html

...and another:

http://www.du.edu/~jcalvert/math/parabola.htm

Neil,
What do you mean by: "A series of radii -- increase one by the same amount as you decrease the other..." ?
Thanks...

It uses the mathematical formula, it finds 3 points, it marks in the DataCAD, and it creates a curve binding these 3 points.