PyXPlot

Examples - Labelled Triangles

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Labelled diagrams of triangles

Script

set unit angle nodimensionless

# Define subroutine for drawing triangles
subroutine TriangleDraw(Bx,By,AB,AC,BC)
 {
  # Use cosine rule to find interior angles
  ABC = acos((AB**2 + BC**2 - AC**2) / (2*AB*BC))
  BCA = acos((BC**2 + AC**2 - AB**2) / (2*BC*AC))
  CAB = acos((AC**2 + AB**2 - BC**2) / (2*AC*AB))

  # Positions of three corners of triangle
  Cx = Bx + BC          ; Cy = By
  Ax = Bx + AB*cos(ABC) ; Ay = By + AB*sin(ABC)

  # Draw triangle
  line from Ax,Ay to Bx,By
  line from Ax,Ay to Cx,Cy
  line from Bx,By to Cx,Cy

  # Draw angle symbols
  ArcRad = 4*unit(mm) # Radius of angle arcs
  arc at Bx,By radius ArcRad from  90*unit(deg)-ABC to  90*unit(deg)
  arc at Cx,Cy radius ArcRad from -90*unit(deg)     to -90*unit(deg)+BCA
  arc at Ax,Ay radius ArcRad from  90*unit(deg)+BCA to 270*unit(deg)-ABC

  # Label lengths of sides
  set unit of length cm # Display lengths in cm
  set numeric sigfig 3 display latex # Correct to 3 significant figure
  TextGap = 1*unit(mm)
  text "%s"%(BC) at (Bx+Cx)/2,(By+Cy)/2 gap TextGap hal c val t
  text "%s"%(AB) at (Ax+Bx)/2,(Ay+By)/2 gap TextGap rot  ABC hal c val b
  text "%s"%(AC) at (Ax+Cx)/2,(Ay+Cy)/2 gap TextGap rot -BCA hal c val b

  # Label angles
  set unit of angle degree # Display angles in degrees
  ArcRad2 = 1.4 * ArcRad # Distance of text from apex of angles
  text "%s"%(CAB) at Ax+ArcRad2*sin(ABC-BCA),Ay-ArcRad2*cos(ABC-BCA) hal c val t
  text "%s"%(ABC) at Bx+ArcRad2*cos(ABC/2),By+ArcRad2*sin(ABC/2) hal l val c
  text "%s"%(BCA) at Cx-ArcRad2*cos(BCA/2),Cy+ArcRad2*sin(BCA/2) hal r val c

  # Label points ABC
  text "A" at Ax,Ay gap TextGap hal c val b
  text "B" at Bx,By gap TextGap hal r val c
  text "C" at Cx,Cy gap TextGap hal l val c
 }

# Display diagram with three triangles
set multiplot ; set nodisplay
call TriangleDraw(2.8*unit(cm),3.2*unit(cm), 3*unit(cm),4*unit(cm),4*unit(cm))
call TriangleDraw(0.0*unit(cm),0.0*unit(cm), 3*unit(cm),4*unit(cm),5*unit(cm))
call TriangleDraw(6.5*unit(cm),0.0*unit(cm), 3*unit(cm),3*unit(cm),3*unit(cm))
set display ; refresh
      

Notes

In this example, we make a subroutine to draw labelled diagrams of the interior angles of triangles, taking as its inputs the lengths of the three sides of the triangle to be drawn and the position of its lower-left corner. The subroutine calculates the positions of the three vertices of the triangle and then labels them. We use PyXPlot's automatic handling of physical units to generate the LaTeX strings required to label the side lengths in centimetres and the angles in degrees. We use PyXPlot's arc command to draw angle symbols in the three corners of a triangle.