Drawing a circle with small radius

[Martin Mueller]

Dear Statalist members

I like to draw multiple circles with varying radius and centers as part of a more complex graph. Thus, I used the - twoway function - command for creating the upper and lower half circle.

    local r = 0.2
    local x0 = 3
    local y0 = 2
    local x_range_l = (`x0'-`r')
    local x_range_u = (`x0'+`r')

    twoway (function y = `y0' - sqrt(`r'^2 - (x - `x0')^2), n(300) range(`x_range_l' `x_range_u') ) ( function y = `y0' + sqrt(`r'^2 - (x - `x0')^2), n(300) range(`x_range_l' `x_range_u') aspect(1) )

However, in some smaller circles (depending on the radius) the two parts of the half circles are not closed to one circle (see picture).






I assume it is because of the number of evaluated points. Because when I change the number of evaluated points to 300000, building the graph is very very slow, but the results look better.

Do you have any ideas, how to improve my circle without loosing that much speed ?


Thank you in advance.
Martin

[FernandoRios]

Hi Martin,
I think you will be successful if you try to build the circles using polar coordinates:

clear
 
range theta 0 2*_pi 100

gen x = 2*sin(theta)
gen y = 2*cos(theta)

line y x, aspect(1)

HTH

[Martin Mueller]

Dear Fernando

Worked like a charm! Perfect.
Thank you!

Best wishes
Martin