Policy vis-a-vis Help
I have verified that this page and applet run on new versions of Explorer and Netscape.
Users have reported success on Macintosh and Linux systems. However, it has also
been verified that the applet in particular will fail on various older and/or less
well-established browsers. My policy is that I will tell people how others got it
to run but I am not going to spend a lot of time and effort helping people to get
it to run under some other OS or browser. I will accept and incorporate
helpful ideas from any tech-minded folks who can make a contribution, but the offer
is "as is, where is."
Some of the material in these notes may be considered arcane. Sorry, but a full,
technical description is more likely to elicit helpful advice from someone who
knows the answer (especially if I have revealed my ignorance).
Stop reading at the point that you don't understand.
version 1.4 (October 1998).
All calculated numbers that appear on the form are rounded to 2 decimal places. Due
to the peculiarity of computer arithmetic, some numbers appear with a string of decimal
zeros and with a final digit in the trillionth place. Sorry. Consider it a reminder that
computer arithmetic is not exact.
2. Mathematical methods.
The calculations of sail area are made by defining a central point by averaging the
coordinates of the corners. Using this point as a common vertex, the sail is divided
into four triangles. The area of each triangle is calculated by Heron's Formula. The
center of each triangle is determined by averaging the vertices. Total area and
center of area of each sail are determined by summing, and taking the weighted average.
Simple experiments indicate that the calculations are correct for normal sail shapes.
However, if a sail is a non-convex shape, e.g. like a boomerang, then the
"central" point may fall outside the permeter of the sail, giving rise to
error. In addition, due to the peculiarities of computer
arithmetic, Heron's Formula may give erroneous answers for very thin triangle shapes,
as might arise if the "gaff" side of the sail was made very short to imitate the
headboard of a bermudan sail.
3. The applet.
I anticipate that many users will have trouble getting the applet to run and draw
the rig shape as desired. Here is a brief summary of possible problems,
If the words "rigDraw Applet here!" appear in the third row of the blue
panel and not a rectagular drawing area, then the applet has not loaded. Alternately,
there may be a blank rectangle and an "Applet not found" message. Either
you are not accessing the Calculator from a proper place or the brower is looking
in the wrong place for it. I got this error using the Star Office browser with the source
on GeoCities; other browsers worked normally.
- Applet fails to load
Browser lacks a Java plug-in
Execution of an applet requires a programming feature called a "Java plug-in."
Most browsers will prompt the user to download one when called for.
Applet fails to start
If the drawing area appears but remains blank when the page is loaded, then
the applet was not successfully started. An error of some kind may be displayed by
the browser. For example, a couple of users have reported the error "Wrong version number"
when using Netscape 4.7. The only solution to this that I know is to get newer browser
software. Upgrading from 4.7 to 6.2 solved the Netscape problems. It is probably only
necessary to upgrade the Java plug-in, but I don't know for sure and that may be a
tricky thing to do.
Applet fails to draw
The applet may start and draw the "three square" initial screen, but then fail
to draw properly when the "Calculate" button is clicked. The likely reason is that
the browser does not support the technology being used.
method of the applet. This functionality is non-standard. In Netscape, it is implemented
by LiveConnect (tm) technology. In Explorer, it is implemented through ActiveX (tm)
technology. Any other-named browser might use one of these, or something else, or
not support the functionality at all. The only fix I can offer is to use a new version
of Netscape or Explorer.
If the applet doesn't run, and the suggestions in these notes don't help, then
I am not going to be able to help either without some more information. In particular,
look for error messages displayed by the browser (usually in the lower left border), and
look in the browser's menus under "Tools", or "Options" for a debugging tool, e.g.
best I am going to be able to do is suggest a fresh install of Netscape or Explorer.
4. Cookie crumbs.
The Save/Recall feature is based on cookies. If the browser has cookies disabled,
this feature obviously won't work. In addition, use of this feature has the
potential for interfering with other cookies, e.g. web site passwords. Netscape,
for example, has a fairly low limit (300) of the total number of cookies allowed
for all sites. Finally, use of the "Delete" feature may delete cookies other than
the ones explicitly targeted. (They would be related to the Calculator page, or the
server from which it was read and would probably have been created by the host
for some record-keeping purpose of its own.)