Math-problem

artmusicstudio

hi,
i cannot find my mistake

with

@run = 30
@lwidthplus = 20

the formula

angle2 = (Math.tan(@lwidthplus/@run))*180/Math::PI

does not give me the right angle.

as far , as i understand

(Math.tan(@lwidthplus/@run)) gives me the RAD

and

*180/Math::PI should give me the degrees

any idea, where my mistake is?

thanx stan

TIG

The numeric methods:

.degrees
.radians

will do the conversions for you.
No need for PI and convolutions...

AND use floats for length, angles etc, rather than integers [which are OK for 'counting' but not any maths]:
30.0 not 30
180.0 not 180
etc
Because
20 / 30 >> 0
whereas
20.0 / 30.0 >> 0.666666666666667
etc

icehuli

try

@run = 30.0
@lwidthplus = 20.0

p.s. are you sure that you are using Math.tan instead of Math.atan ?

artmusicstudio

hi tig & icehuli,

@tig: yes, the numbers come from another modules and should be float (with direct input "45.degrees" in tr for angle2 the object is turned by 45 degr.)

in the code below i tried the 'simple way', not clear to me, why it still does not work

@icehuli
see the code, the function should be the right one


        new_line = @entities2.add_line pfm1, pfm2 # gives vertical line	
	@vector = new_line.line[1]
	point = [0,0,0]
#
	angle = (Math.tan(@lwidthplus/@run)) # x,y come from another module
	angle2 = angle.degrees # trying to become degrees
#
        puts "@lwidthplus",@lwidthplus #gives >> 7.8740157480315 (equiv. to 20)
	puts "@run",@run #gives >> 11.8110236220472(equiv. to 30)	
        puts angle  #gives >> 1.5574077246549, should be 0,6666666 ( = 20/30 >> about 34 degr.)
	puts angle2  #gives >> 0.0271818925912213
#
	tr = Geom;;Transformation.rotation(point,@vector,angle2) # turnes somehow 
	group.entities.transform_entities(tr, group.entities.to_a)
#        
	@m_pf_l = group.to_component
	defn = @m_pf_l.definition
	defn.name = "@m_pf_l"

it must be something very simple....but i cannot see it!

stan

TIG

You confuse methods...
angle.degrees makes the number into radians - useful of you want to input user-friendly values like 45.degrees >> 0.785398163397449 radians is much more intuitive than Math::PI/4.0 >> 0.785398163397448 radians etc

Then
angle.radians makes the number into degrees - useful if you have calculated an angle in radians but want it displaying in a user-friendly degree format... 0.785398163397448.radians >> 45.0 degrees

artmusicstudio

hi tig, ok. i will make tests and learn.
but anyway:

why does

angle = Math.tan(20.0/30.0)

give (by puts angle)

0.786842889472977

instead of

0.66666666 (normal tangens)

and if 0.786842889472977 = 20/30 in radians,

why does angle.radians then not give 33.69 degrees?

sorry, i am confused, i seem to misunderstand someting totaly...

stan

icehuli

if 20.0 and 30.0 are the edges, 20.0/30.0 is already the tangent value. You should use Math.atan to get the angel out of it.
so in short:

angel = (Math.atan(@lwidthplus/@run)).radians

artmusicstudio

hi icehuli,
that's it! of course, i already had the tanges, so......sometimes it's so clear afterwards...
thanx a lot, the method works now!


new_line = @entities2.add_line @pfm1, @pfm2	
@vector = new_line.line[1]
point = [0,0,0]
angle = (Math.atan(var4/@run)).radians 
angle = 360 - (Math.atan(var4/@run)).radians  if var5 == "right"
tr = Geom;;Transformation.rotation(point,@vector,angle.degrees)
@group.entities.transform_entities(tr, @group.entities.to_a)

stan