Added catenary curves.

tests/catenary.scad

@@ -0,0 +1,56 @@
+//
+// NopSCADlib Copyright Chris Palmer 2020
+// nop.head@gmail.com
+// hydraraptor.blogspot.com
+//
+// This file is part of NopSCADlib.
+//
+// NopSCADlib is free software: you can redistribute it and/or modify it under the terms of the
+// GNU General Public License as published by the Free Software Foundation, either version 3 of
+// the License, or (at your option) any later version.
+//
+// NopSCADlib is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+// without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along with NopSCADlib.
+// If not, see <https://www.gnu.org/licenses/>.
+//
+l = 250; // [1: 1000]
+x = 200; // [1: 1000]
+y = 50; //[-500 : 500]
+
+include <../utils/core/core.scad>
+use <../utils/catenary.scad>
+use <../utils/sweep.scad>
+use <../utils/annotation.scad>
+
+module catenaries() {
+    //
+    // catenary curve path from control points
+    //
+    curve = [for(p = catenary_points(l, x, y)) [p.x, p.y, 0]];
+    //
+    // Draw the curve
+    //
+    r = 0.5;
+    sweep(curve, circle_points(r, $fn = 64));
+    //
+    // Minimum Z
+    //
+    min_z = catenary_points(l, x, y, 0);
+
+    color("blue") {
+        translate([min_z.x, min_z.y + r])
+            rotate([-90, 0, 0])
+                arrow();
+
+        translate([min_z.x, min_z.y - r])
+            rotate([90, 0, 0])
+                arrow();
+    }
+}
+
+if($preview)
+    rotate(is_undef($bom) ? 0 : [70, 0, 315])
+        catenaries();