Calculating angles

I am using the PolarPoint method:

endPoint = ThisDrawing.Utility.PolarPoint( _
objCoord, dPolarRotate, dPolarDistance)

I have come to the situation where I know the 3 lengths of my triangle (90 degrees triange) and want to work out the longest sides angle so that I can use it with PolarPoint. How do I calculate the angle? The arcsin derived idea on the VBA help is not foolproof and crashes for certain angles.

Thanks.

 

I decided to use two PolrPoint methods to mimic the lines of the rectangle. I end up with the coordinate I need.

This is good enough for me.

 

Just to tie up a loose thread, the derived function in the help file is:
Arcsin(X) = Atn(X / Sqr(-X * X + 1))

It will crash when X=1 or X=-1. To make it work you would wrap it in an
IF-THEN to catch these cases, such as:

Dim asin as double
const PI = 3.1415 'approximate
If X = 1 then
asin = PI / 2 '90 degrees
elseif X = -1 then
asin = 3 * PI / 2 '270 degrees or -90deg
else
asin = Atn(X / Sqr(-X * X + 1))
endif

James

degrees triange) and want to work out the longest sides angle so that I can
use it with PolarPoint. How do I calculate the angle? The arcsin derived
idea on the VBA help is not foolproof and crashes for certain angles.

 

In addition, Arcsin is undefined for any values of X outside ±1, so you may want an extra clause such as:

ElseIf X < -1 Or X > 1 Then
MsgBox X & " is outside the pure mathematical definition of Arcsin"

Regards

Wayne Ivory
IT Analyst Programmer
Wespine Industries Pty Ltd

 

Why doesn't someone just define some decent derived methods, like a good working arcsin and make them available for users to download?

Andrew

 

Hi Andrew,

I've been on a large number of sites on the web where this type of data is
published for free download. Maths text books are full of it and when I
went to school you would have been locked at about year 10 maths until such
time as you could do it yourself.

Before complaining you should have done a web search.

--


Laurie Comerford
CADApps
www.cadapps.com.au

working arcsin and make them available for users to download?

 

I was not complainign as such. And please trust me, I did a websearch about asin.

You must appreciate I am not a mathematical wizard and I did not do trigonometry at school. The webpages that I found showed stuff I did not understand.

What I was getting at is this:

Autodesk go to the trouble of providing a help topic showing a derived method for arcsin (as I already find myself by doing searching through help topics ). But it would have been nice to show a fully working derivation and not just a snippet that by itself is not good enough.

That was all.

But please, I check websites alot and serach engines, so don't mis-construe what I was saying.

 

In fairness to Autodesk, if you're going to blame anyone then blame Microsoft because they provided the Visual Basic engine used in AutoCAD along with the half-baked arcsin example.

Regards

Wayne Ivory
IT Analyst Programmer
Wespine Industries Pty Ltd