Rotating line

[nemesest]

Hi, I'm a grade 11 computers student and I'd like to know:


how would I make a line, outside a circle and touching it, go around the circle.

/
O

O--

etc..

So the line would rotate around the circle.

It's for making a radar program that I plan to use for history presentation.

Thanks

[Clayton]

you could use trig to find the angle you want it to move to next, or you could use the equation of a circle somehow to find all points on your circle (x^2+y^2=r^2) and draw lines around your central point to the point on that circle

[Delos]

I would suggest sticking with the Trig concepts. Incorporating loci is just a little too complicated for as simple a task as this.
Base your programme on triangles and the Pythagoras theorem. At any given point, you'll be drawing the hypotenuse of a triangle whose length will be the radius of the circle. Cycle through all 360 degrees of that circle, using Trig to determine the Opp and Adj lengths; which will allow you to calculate coordinates.
You might need these commands:

code:

sind () cosd () tand () Math.Distance ()

If the version of Turing you're using does not have Math.Distance (), it's a sinch to make. It's just Pythagoras theorem, nothing more.

[do_pete]

You could also draw one picture and use Pic.Rotate to rotate it.

[Clayton]

actually Delos, the Math.Distance isnt pythagorean theorem(idk how to spell that lol), its more the distance of a line, if you dont have it you can make it like this

Turing:

fcn Math_Distance (x,y,x2,y2:int):real     result sqrt((x2-x)**2+(y2-y)**2) end Math_Distance

simple enuf right?

[do_pete]

Yes it is...

a^2+b^2=c^2
(a^2+b^2)^0.5=(c^2)^0.5
(a^2+b^2)^0.5=c

[Clayton]

ah but the distance formula is the change in x and y, not just a point you have (which is what you are trying to say in your above eqn) so you have to use the distance formula (or at least it is more handy, and works in exactly the same way as Math.Distance

[zylum]

code:

View.Set ("offscreenonly") const r := 20 const R := 100 const rotationSpeed := 1 var theta : int := 0 loop     Draw.Oval (maxx div 2, maxy div 2, r, r, black)     Draw.Line (round (cosd (theta) * r + maxx div 2), round (sind (theta) * r + maxy div 2), round (cosd (theta) * R + maxx div 2), round (sind (theta) * R + maxy div 2), black)     theta += rotationSpeed     View.Update     delay (20)     cls end loop

just need sin and cos

[do_pete]

SuperFreak82 wrote:

ah but the distance formula is the change in x and y, not just a point you have (which is what you are trying to say in your above eqn) so you have to use the distance formula (or at least it is more handy, and works in exactly the same way as Math.Distance

Um... the distance formula is Pythagorean's Therom, it just uses x1-x2 as a y1-y2 as b. And it is not the change in x and y but the difference between the two values.

[codemage]

How about just doing a Draw.FillArc?

If you make it only a few degrees wide, it'll look like a line, and then all of the trig is done for you, and it's automatically centred on your circle's coordinates. (You just put in the angles, and it draws).

[Albrecd]

Or you could draw the line first from (maxx div 2, maxy div 2) to points that gradually move around the perimeter of the screen (preferably roughly a circle beyond the edges of the screen. [The circle formula as stated by SuperFreak82 would be useful for this]). You could then just draw the circle overtop in the centre of the screen.

[zylum]

or you could do it properly and do it my way. its not like there's anything hard about it.

[Cervantes]

nemesest wrote:

how would I make a line, outside a circle and touching it, go around the circle.
...
It's for making a radar program that I plan to use for history presentation.

I'm confused. The first line suggests to me that you want to draw a line tangent to the circle, and move that line around the circle, keeping it always tangent. But the second line (the word "radar" in particular) suggests to me that you want to draw the line from the centre of the circle to the edge of the circle, and move that point on the edge of the circle around the circle.

[NikG]

codemage wrote:

How about just doing a Draw.FillArc?

If you make it only a few degrees wide, it'll look like a line, and then all of the trig is done for you, and it's automatically centred on your circle's coordinates. (You just put in the angles, and it draws).

I'm not sure how much difference there is between Draw.FillArc and drawfillarc but don't do it that method! It's very unrealiable (sometimes, it fills all angles except the ones you want for no reason).

[jamonathin]

NikG wrote:

don't do it that method! It's very unrealiable (sometimes, it fills all angles except the ones you want for no reason).

I'd like you to show me what you mean. Oh wait here's an example

code:

setscreen ("offscreenonly") var angle1, angle2 : int := 0 angle2 := 2 loop     angle1 += 1     angle2 += 1     if angle1 > 360 then         angle1 := 1     end if     if angle2 > 360 then         angle2 := 1     end if     cls     Draw.FillArc (maxx div 2, maxy div 2, 100, 100, angle1, angle2, black)     View.Update     exit when hasch end loop

Very unreliable . . .