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From: Peter Proost on 28 Apr 2010 03:14
Hi group,

I have got a math/drawing question and as the question will show my math
knowledge is of toddler level...

I've got a line going from x1,y1 to x2,y2 then the user inputs an angle
and a length for a second line starting from x2,y2 going to x3,y3
But how do I calculate the value for x3,y3? I think I need to do
something with cosinus and sinus and my angle and length but I don't
know what.

Thanks in advance,


Greetz,

Peter
From: Andrew Morton on 28 Apr 2010 04:28
Peter Proost wrote:
> I've got a line going from x1,y1 to x2,y2 then the user inputs an
> angle and a length for a second line starting from x2,y2 going to
> x3,y3 But how do I calculate the value for x3,y3? I think I need to do
> something with cosinus and sinus and my angle and length but I don't
> know what.

x3=x2+r*cos(t)
y3=y2+r*sin(t)

where r is the length (commonly referred to as the radius in this situation)
and t is the angle in radians (theta, angles are usually called theta for
these things).

(angle in radians)=(angle in degrees)*pi/180

And don't forget that the screen y-axis is upside-down compared to what
you'd draw with pencil and paper.

--
Andrew


From: Peter Proost on 28 Apr 2010 04:40
On 28/04/2010 10:28, Andrew Morton wrote:
> Peter Proost wrote:
>> I've got a line going from x1,y1 to x2,y2 then the user inputs an
>> angle and a length for a second line starting from x2,y2 going to
>> x3,y3 But how do I calculate the value for x3,y3? I think I need to do
>> something with cosinus and sinus and my angle and length but I don't
>> know what.
>
> x3=x2+r*cos(t)
> y3=y2+r*sin(t)
>
> where r is the length (commonly referred to as the radius in this situation)
> and t is the angle in radians (theta, angles are usually called theta for
> these things).
>
> (angle in radians)=(angle in degrees)*pi/180
>
> And don't forget that the screen y-axis is upside-down compared to what
> you'd draw with pencil and paper.
>


Thanks a lot exactly what I needed. I was already aware of the .net y
axis being upside-down

Thanks again
From: Peter Proost on 28 Apr 2010 05:04
Hi,


I've got an extra question which I forgot to mention in my original
post. Thanks to your answer I can calculate x3,y3, but they need to be
calculated with respect to the angle of the x1,y1 - x2,y2 line. I hope
you get what I mean.

Thanks again,

Peter

From: Andrew Morton on 28 Apr 2010 05:44
Peter Proost wrote:
> I've got an extra question which I forgot to mention in my original
> post. Thanks to your answer I can calculate x3,y3, but they need to be
> calculated with respect to the angle of the x1,y1 - x2,y2 line. I hope
> you get what I mean.

Angle of line (p1,p2) in radians=atan2(y2-y1, x2-x1) where p1=(x1,y1) and
p2=(x2,y2).

I recommend that you keep all angles in the code in radians, and only do the
degrees<->radians conversions at the user-interface level.

HTH

--
Andrew


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