Convert rise and run (slope) to degrees using simple formulas

[Alaskan Son]

I'm looking for a little help here. I'm just a relatively regular Joe here though, so any complicated formulas are likely to go right over my head. What I'm trying to do is use the Ruby programming language to convert rise and run (slope) to degrees. See the attached screenshot...

View attachment 8617

Assume x and y-axis are constant and that point a is always at 0,0. I want to use dimension d and e to obtain an angle in degrees. In this example:

d = 334.385384
e = 187.413131

I happen to know that angle c = approx. e° due to some tools I have available in my CAD program, but I really want to be able to plug d and e into a formula so I can get some automated feedback using some Ruby scripting. Ruby has an Arc Tangent function...

View attachment 8618

...but I'm really not sure how to use it. I tried using atan(e/d) but that results in 0.5108463979434283

I'd love if someone could help me understand what I'm doing wrong. Thanks.

 

[I like Serena]

I'm looking for a little help here. I'm just a relatively regular Joe here though, so any complicated formulas are likely to go right over my head. What I'm trying to do is use the Ruby programming language to convert rise and run (slope) to degrees. See the attached screenshot...
Assume x and y-axis are constant and that point a is always at 0,0. I want to use dimension d and e to obtain an angle in degrees. In this example:

d = 334.385384
e = 187.413131

I happen to know that angle c = approx. e° due to some tools I have available in my CAD program, but I really want to be able to plug d and e into a formula so I can get some automated feedback using some Ruby scripting. Ruby has an Arc Tangent function...
...but I'm really not sure how to use it. I tried using atan(e/d) but that results in 0.5108463979434283

I'd love if someone could help me understand what I'm doing wrong. Thanks.

Hi Alaskan Son,

I presume your problem is that you want the angle in degrees?

You are getting the result in so called radians.
To get degrees you need to multiply by [m]180 / Math::PI[/m].
So for instance [m]atan2(1,1) * 180 / Math::PI[/m] = 45.

 

[Joppy]

Just as an aside, I recommend that you be consistent with the way you label your axis. For instance, moving counter clockwise from axis labelled 0 degrees in your diagram, we go to +90, +180, +270 (not -90) and then +360 = 0. This might not be an issue now, but later on it might make things a little awkward. In general, it's good to fix any conventions/rules from the beginning.

I usually go one step further when dealing with this situation and modulo the output of atan2 such that the result is a positive angle measured counterclockwise.

 

[Alaskan Son]

Hi Alaskan Son,

I presume your problem is that you want the angle in degrees?

You are getting the result in so called radians.
To get degrees you need to multiply by [m]180 / Math::PI[/m].
So for instance [m]atan2(1,1) * 180 / Math::PI[/m] = 45.

Awesome! Thanks : )

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Just as an aside, I recommend that you be consistent with the way you label your axis. For instance, moving counter clockwise from axis labelled 0 degrees in your diagram, we go to +90, +180, +270 (not -90) and then +360 = 0. This might not be an issue now, but later on it might make things a little awkward. In general, it's good to fix any conventions/rules from the beginning.

I usually go one step further when dealing with this situation and modulo the output of atan2 such that the result is a positive angle measured counterclockwise.

Thanks you, but I purposely labeled them like that. Those are the way angles are used in my drafting program and my goal is to have angles that report in those exact formats. Now that I have the proper formula, I think I can make it work.

Actually, upon further investigation, the following formula results in exactly what I was looking for...

(Math.atan2(y_position,x_position)*180)/Math::PI

Thanks again guys.

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...I happen to know that angle c = approx. e° ...

Just curious. I actually entered a long decimal angle number in my post yesterday. It was automatically changed after I posted it though and I didn't realize it until now. Do you guys happen to know why my number might have been changed to "eÂ"??