• Two figures are perspective from a point provided the lines determined from corresponding points are concurrent. The point is called the center.
   

• Two figures are perspective from a line provided the points of intersection of corresponding sides are collinear. The line is called the axis.
  Examples. The first figure illustrates triangles perspective from a point. The second figure illustrates triangles perspective from a line.

Explore Perspective from a Point

Drag any of the three points determining the two triangles.
Drag the center O and the points determining the lines a, b, and c.

Explore Perspective from a Line

Drag the points  l₁ or l₂  of the line to change the axis l.
Drag the points X, Y, Z, A, A', C, or C' to change the triangles.

Timothy Peil, 4 February 2013, Created with GeoGebra