[Tutor] Using trigonometry to draw a circle

[Phil]

On 18/5/21 8:06 pm, David wrote:

>> wxPython's addArc function, for example, works well but I cannot see how
>> I can set points along the arc. If I plot individual points to generate
>> an arc then setting points along the arc is easy.

> Depending on why you are doing this, there are different approaches
> that might or might not be a good idea. So you will get better advice
> if you describe the bigger picture of what you are doing, not the details.

Thanks David,

At the moment I'm playing with wxPython and I'm reluctant to go too 
deeply into wxPython code because this is not a wxPython list. I'm 
trying to simulate an analogue meter and the current approach is to use 
the path.AddArc function to draw the meter arc. Now I'd like to add 
ticks along the arc; I cannot see how to do this.

So now I'm experimenting with drawing the arc with a for loop to 
calculate each point and then setting the points on the frame. So far so 
good, now to add the ticks. The ticks should be short lines centred on 
the arc and extending a little on each side of the arc towards the 
centre of the arc. As I see it, this requires more calculations to 
determine the end points of the ticks. I have the x, y coordinates of 
where the ticks should be centred on the arc, I know the length of the 
ticks and I know the distance to the centre of the arc.

Another approach that I've considered is to draw the meter in a drawing 
application, or use the Python pil library. Then I could display the 
meter and rotate the needle about it's pivot point. I haven't looked 
into the finer points of this approach but it would avoid lots of 
calculations every time the meter has to be updated.

Your matplotlib code is very close to what I have in mind and I've saved it.

-- 

Regards,
Phil