Hcfyk

Based on this tutorial, I understand symbols -| and |- are used to draw perpendicular lines.

But I wish to understand the difference between the two.

There are the following related questions:

1. Insertion of perpendicular symbol at intersection of two perpendicular lines


2. How to add perpendicular symbol at desired location


3. How to Mark Right Angle in Tikz

But none of them seem to use the approach of -| and |-.

Understand it as it looks like:

• 
  

  -| is "horizontal line → vertical line":

  
  
  

  documentclass[tikz]standalone
  begindocument
  begintikzpicture
  draw (0,0) coordinate (1) node[below] $(0,0)$;
  draw (2,2) coordinate (2) node[above] $(2,2)$;
  draw (1) -| (2);
  % -------------
  draw (4,2) coordinate (x) node[above] $(4,2)$;
  draw (6,0) coordinate (y) node[below] $(6,0)$;
  draw (x) -| (y);
  endtikzpicture
  enddocument
  

  
  
  

  

  
  
  

  Mathematically, (x,y) -| (a,b) and (x,y) -- (a,y) -- (a,b) are the same.

  
  


• 
  

  |- is "vertical line → horizontal line":

  
  
  

  documentclass[tikz]standalone
  begindocument
  begintikzpicture
  draw (0,0) coordinate (1) node[below] $(0,0)$;
  draw (2,2) coordinate (2) node[above] $(2,2)$;
  draw (1) |- (2);
  % -------------
  draw (4,2) coordinate (x) node[above] $(4,2)$;
  draw (6,0) coordinate (y) node[below] $(6,0)$;
  draw (x) |- (y);
  endtikzpicture
  enddocument
  

  
  
  

  

  
  
  

  Mathematically, (x,y) |- (a,b) and (x,y) -- (x,b) -- (a,b) are the same.

  
  

They are clearly very different.

I'd like to add to JouleV's answer another use of -| and |-.

Given two nodes, A and B:

• if you use (A |- B) you have a point with the x coordinate of A and the y coordinate of B


• if you use (A -| B) you have a point with the x coordinate of B and the y coordinate of A.

documentclassarticle
usepackageamsmath
usepackagetikz
usetikzlibrarypositioning

begindocument
begintikzpicture
node[draw] (A) A;
node[draw, above right =4cm of A] (B) B;
node[draw] at (A |- B) $x$ of A, $y$ of B;
node[draw] at (A -| B) $x$ of B, $y$ of A;
endtikzpicture
enddocument

PSTricks version for @CarLaTeX's explanation:

• 
  (A|-B) (TikZ) = (A|B) (PSTricks)


• 
  (A-|B) (TikZ) = (B|A) (PSTricks)