Calculate rotated ellipse position given two points on it's circumference

[dinther]

How can anyone not prefer this over the "wall of text" even though, I understand ownership issues as I don't trust big tech myself anymore. But currently you have participation issues. Maybe the wall off text method should continue to be used for openSCAD developers while making access to openSCAD users more friendly? Because currently they are all over the place from thingyverse to reddit.

$fa = 6;

module polyline(pts, w = 1, c=false) {
    pts=c? concat(pts,[pts[0]]) : pts;
    for(i = [0:len(pts)-2]) hull(){ translate(pts[i]) circle(d=w,$fn=16); translate(pts[i+1]) circle(d=w); }
}

function ellipse(rx, ry) = let( s = $fn>0?($fn>=3?$fn:3):ceil(max(min(360/$fa,abs((rx+ry)/2)*2*PI/$fs),5)), step = 360/s)
[for (i=[0:s]) [cos(i*step)*rx, sin(i*step)*ry]];

function ellipseCenter(last=[0,0], p2=[], rx, ry, fA, fS, angle)= let(
P = [[cos(angle), sin(angle)], [-sin(angle), cos(angle)]] * ((last-p2)*0.5),
x1p = P[0], y1p = P[1],
lambda =  ((x1p * x1p) / (rx * rx) ) + ( (y1p * y1p) / (ry * ry) ),
rx = lambda > 1? (sqrt(lambda) * abs(rx)) : abs(rx),
ry = lambda > 1? (sqrt(lambda) * abs(ry)) : abs(ry),
flip = fA == fS? -1 : 1,
co = (fA == fS? 1 : -1) * sqrt(( (rx*rx*ry*ry) - (rx*rx*y1p*y1p) - (ry*ry*x1p*x1p) ) / ( (rx*rx*y1p*y1p) + (ry*ry*x1p*x1p) )),
Cp = [rx*y1p/ry, -ry*x1p/rx] * co,
C = ([[ cos(angle), -sin(angle)],[sin(angle), cos(angle)]] * Cp) + ((last+p2)*0.5)) C;

rx = 100;
ry = 150;
p_g = [-10,200];
p_r = [100,50];
angle = 30;

center = ellipseCenter(p_g,p_r,rx, ry, 1, 1, angle);
pts = ellipse(rx,ry);
translate([center[0],center[1],0]) rotate(angle) polyline(pts);
translate(p_g) color("green") circle(r=3);
translate(p_r) color("red") circle(r=3);

ellipse_rotate.mp4

[dinther]

Reply with video after delete reply..

Editor.mp4

[jordanbrown0]

Forum vs e-mail seems to be a religious matter. It's been established that, for whatever reason, a large majority of the participants on the OpenSCAD mailing list prefer e-mail.

I can't imagine trying to track N independent topics (OpenSCAD, OpenSSL, OpenLDAP, my Scout troop, blogs, et cetera) using N different web pages with N different user interfaces, that I must individually visit.

Even within one topic - say, OpenSCAD - I can't imagine tracking N conversations each of which must be individually visited to find new leaves in the conversation tree.

The solution to both of those is for the conversations to be fed to me in a single linear feed, and indeed most forums do that by sending notifications... at which point they act a lot like mailing lists, just with awkward user interfaces and poor addressing semantics.

Note, for instance, that I cannot send you a private message using this mechanism. If I want to tell you about an embarrassing mistake in your program, or I want to scold you for misbehavior, it must be done in public. "Praise in public, criticize in private.".

[jordanbrown0]

BTW, when the "why isn't this a forum" topic comes up, one of the replies is usually "if you like a forum UI better, why don't you use Reddit or Facebook or the Thingiverse group?", and and answer is "but this is where the cool kids hang out". Since the majority of the users on the mailing list prefer e-mail, it seems that sometimes you must choose which is more important to you: the group of people, or the user interface.

[jordanbrown0]

Also, I haven't done a survey recently but I think the volume on the mailing list is a couple of times larger than all of the other venues combined.