I'm ashamed to have to ask this, but I just can not remember how to
calculate an angle in degrees if I know the opposite and adjacent side of a
right-angled triangle.

My only excuse is that I'm an OAP and school was just years ago and then
radians were not taught!

Help!

Thanks
Zog

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TheMightyZog schrieb:
> I'm ashamed to have to ask this, but I just can not remember how to
> calculate an angle in degrees if I know the opposite and adjacent side of a
> right-angled triangle.
> 
> My only excuse is that I'm an OAP and school was just years ago and then
> radians were not taught!
> 
> Help!
> 
> Thanks
> Zog
> 
> 

If it looks like this

        alpha
      /|
   h /=|
    /  | o
   /  .|
   -----
     a

alpha = atan (a/o)
alpha = acot (o/a)
alpha = asin (a/h)


Is this what you wanted ... POVCODE?

Marc

Post a reply to this message

Marc Schimmler <mar### [at] webde> wrote:
> TheMightyZog schrieb:
> > I'm ashamed to have to ask this, but I just can not remember how to
> > calculate an angle in degrees if I know the opposite and adjacent side of a
> > right-angled triangle.
> >
> > My only excuse is that I'm an OAP and school was just years ago and then
> > radians were not taught!
> >
> > Help!
> >
> > Thanks
> > Zog
> >
> >
>
> If it looks like this
>
>         alpha
>       /|
>    h /=|
>     /  | o
>    /  .|
>    -----
>      a
>
> alpha = atan (a/o)
> alpha = acot (o/a)
> alpha = asin (a/h)
>
>
> Is this what you wanted ... POVCODE?
>
> Marc

Better to use atan2(a,o).  Handles situation where o is zero.
Also note the results of these is in radians to convert to degrees use
degrees(A) in POV (or A*180/pi by hand).

-tgq

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Thank you Marc, but I tried that the following
   rotate<atan(1/2),0,0>
should be the same as
  rotate<30,0,0>
but it is not and atan(1/1) does virtually nothing.
- or am I doing something wrong?

"Marc Schimmler" <mar### [at] webde> wrote in message
news:46703a71$1@news.povray.org...
> TheMightyZog schrieb:
> > I'm ashamed to have to ask this, but I just can not remember how to
> > calculate an angle in degrees if I know the opposite and adjacent side
of a
> > right-angled triangle.
> >
> > My only excuse is that I'm an OAP and school was just years ago and then
> > radians were not taught!
> >
> > Help!
> >
> > Thanks
> > Zog
> >
> >
>
> If it looks like this
>
>         alpha
>       /|
>    h /=|
>     /  | o
>    /  .|
>    -----
>      a
>
> alpha = atan (a/o)
> alpha = acot (o/a)
> alpha = asin (a/h)
>
>
> Is this what you wanted ... POVCODE?
>
> Marc
>

Post a reply to this message

TheMightyZog <Chr### [at] hotpopcom> wrote:
> Thank you Marc, but I tried that the following
>    rotate<atan(1/2),0,0>
> should be the same as
>   rotate<30,0,0>

  It shouldn't because atan() returns radians while rotate takes degrees.

  Besides, you should really use atan2().

-- 
                                                          - Warp

Post a reply to this message

Trevor G Quayle schrieb:

> 
> Better to use atan2(a,o).  Handles situation where o is zero.
> Also note the results of these is in radians to convert to degrees use
> degrees(A) in POV (or A*180/pi by hand).
> 
> -tgq
> 

You are right with regrad to POV, I explained it more the mathematical 
way ...

Marc

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Thanks tgq, but
   rotate<(degrees(atan2(1,2))),0,0>
is not exactly the same as
  rotate<30,0,0>
 - it is a little off as I suspect it is using the arc of a radian circle
instead of straight lines


"Trevor G Quayle" <Tin### [at] hotmailcom> wrote in message
news:web.46703ec3f87630f4c150d4c10@news.povray.org...
> Marc Schimmler <mar### [at] webde> wrote:
> > TheMightyZog schrieb:
> > > I'm ashamed to have to ask this, but I just can not remember how to
> > > calculate an angle in degrees if I know the opposite and adjacent side
of a
> > > right-angled triangle.
> > >
> > > My only excuse is that I'm an OAP and school was just years ago and
then
> > > radians were not taught!
> > >
> > > Help!
> > >
> > > Thanks
> > > Zog
> > >
> > >
> >
> > If it looks like this
> >
> >         alpha
> >       /|
> >    h /=|
> >     /  | o
> >    /  .|
> >    -----
> >      a
> >
> > alpha = atan (a/o)
> > alpha = acot (o/a)
> > alpha = asin (a/h)
> >
> >
> > Is this what you wanted ... POVCODE?
> >
> > Marc
>
> Better to use atan2(a,o).  Handles situation where o is zero.
> Also note the results of these is in radians to convert to degrees use
> degrees(A) in POV (or A*180/pi by hand).
>
> -tgq
>
>
>

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Thanks Warp, but
   rotate<(degrees(atan2(1,2))),0,0>
or
   rotate<(atan2(1,2)),0,0>
is not the same as
  rotate<30,0,0>

- 'tis a real puzzle!

"Warp" <war### [at] tagpovrayorg> wrote in message
news:4670424a@news.povray.org...
> TheMightyZog <Chr### [at] hotpopcom> wrote:
> > Thank you Marc, but I tried that the following
> >    rotate<atan(1/2),0,0>
> > should be the same as
> >   rotate<30,0,0>
>
>   It shouldn't because atan() returns radians while rotate takes degrees.
>
>   Besides, you should really use atan2().
>
> -- 
>                                                           - Warp

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"TheMightyZog" <Chr### [at] HotPOPcom> wrote:
> Thanks tgq, but
>    rotate<(degrees(atan2(1,2))),0,0>
> is not exactly the same as
>   rotate<30,0,0>
>  - it is a little off as I suspect it is using the arc of a radian circle
> instead of straight lines

Of course this isn't the same.  the arctan of 1/2 is ~28.6 degrees not 30.
I.e., the tan of 30 is not 1/2, it's 0.577, you are thinking of sin(30)
which is O/H not O/A:

rotate<(degrees(asin(1/2))),0,0> = rotate<30,0,0>


-tgq

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TheMightyZog <Chr### [at] hotpopcom> wrote:
>  - it is a little off as I suspect it is using the arc of a radian circle
> instead of straight lines

  What does that even mean?

-- 
                                                          - Warp

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