Wallace-Simson Line Construction on a Sphere

①This example demonstrates the construction of the Wallace-Simson line on a sphere: from a point on the sphere, perpendiculars are dropped to the three sides (great-circle arcs) of a spherical triangle, and the three feet are collinear. ②Core mathematical concepts include spherical geometry, great circles, perpendicularity, collinearity, and the generalization of the Wallace-Simson theorem to non-Euclidean surfaces. ③Construction details: using GeoGebra commands such as Sphere, PointIn, Plane, IntersectPath, Circle, Point, OrthogonalLine, Intersect, and Sequence, the construction builds multiple objects (A, a, B, C, D, b, c, d, e, f, g, h, E, i, j, k, l, m, n, p, q, r, F, G, H, s, o, t, I, L_1) to create and verify the collinearity. ④This is suitable for high school to university-level geometry teaching, offering an extension of classical theorems to curved surfaces and serving as an advanced GeoGebra construction example.