Parabola Plotting Web Pages

Graphics have become more available on web pages. A web page that can design parabolas can show what is now available. 

Step 1

 Different applications require parabolas having different focal points. A parabola follows the following equation.

Y = X^2/(4*focal)

The old camera flash bulbs appeared to use a short focal length when compared to its radius. When the focal is 0.25, then Y will be unity when X is unity.

The web page to do this is only a text file. Feel free to save it as source on you computer. 

Comments

[joen]

I tried the web page and nothing happened. Did I miss somethihg

[nutsandbolts_64]

 The unit of measurement in the focal point thing is?

[dsauer]

The focal length corresponds to the radius along the x direction being unity. The web page that plots the segments does do an auto-scale to fill a 700x700 canvas.  

Another write up on what things do can be found here...
 www.idea2ic.com/OtherStuff/Web_parabola/Design_A_parabola.html

[nutsandbolts_64]

 Ok, thanks.

[kelseymh]

On Step 5, you say that you only generate 11 X points, and (implicitly) do a linear interpolation between them.  For focal depths far from 1, this is not optimal.  I played with the script, putting in 0.05 and 0.005 respectively.  In both cases, the straight lines and corners in Y are quite apparent (the latter has just two lines!).

To get a smother curve, you may want to consider evaluating the inverse problem to get Xmax (positive) for Ymax at the boundary of the plot, then generate a fixed number of steps from X=0 to X=Xmax.

Otherwise, this is a very clever bit of JavaScript.  Nicely done!

[dsauer]

Well good. Someone did not treat the web page as a black box. The idea is to show what graphic on a web page can do.

[kelseymh]

:-)  When you said it was a "plain text" file, I got curious.  Nice to see simple scripting, rather than some overwritten applet that gets downloaded to do who knows what.

[dsauer]

 I think the people who write instructables could get really turned on with what they could do with web pages. This stuff could be fun if presented right. My best attempt at doing this can be found here.