Pikchr

A position is a point on the SVG canvas. A place is a specific position associated with an object. Every place is a position, but not every position is a place. This page is about position.

• expr , expr
• place
• place + expr , expr
• place - expr , expr
• place + ( expr , expr )
• place - ( expr , expr )
• ( position , position )
• ( position )
• fraction of the way between position and position
• fraction way between position and position
• fraction between position and position
• fraction < position , position >
• distance which-way-from position

Absolute versus Place-relative Positions

One form of a position is an (X,Y) coordinate pair. This works, but its use is discouraged. It is better to use positions that are either a place or are derived from one or more places.

The "( position , position )" Form

A place of the form "(pos1,pos2)" where pos1 and pos2 are other positions means use the X coordinate from pos1 and the Y coordinate from pos2.

leftmargin = 1cm;
P1: dot; text "P1" with .s at 2mm above P1
P2: dot at P1+(2cm,-2cm); text "P2" with .s at 2mm above P2
dot at (P1,P2); text "(P1,P2)" with .s at 2mm above last dot
dot at (P2,P1); text "(P2,P1)" with .s at 2mm above last dot

"fraction of the way between" Forms

All of these syntactic forms of position are the same:

• fraction of the way between position and position
• fraction way between position and position
• fraction between position and position
• fraction < position , position >

The last form is the most cryptic, but it is also the most compact and hence ends up being the most often used.

In all cases fraction is an expression that usually evaluates to between 0.0 and 1.0. The resulting position is that fraction along a line that connects the first position to the second position.

The fraction can be less than 0.0 or greater than 1.0, in which case the point is on the extended line that connects the two positions.

P1: dot; text "P1" with .s at 2mm above P1
P2: dot at P1+(4cm,1.5cm); text "P2" with .s at 2mm above P2
line thin color gray dotted from -.5<P1,P2> to 1.5<P1,P2>
dot at 3/4<P1,P2>; text "3/4<P1,P2>" at (last dot,P1)
   arrow thin color gray from last text.n to 1mm south of last dot
dot at -0.25 of the way between P1 and P2
   text "-0.25 of the way between P1 and P2" at (last dot,P2)
   arrow thin color gray from last text.s to 1mm north of last dot

"position which-way-from position" Forms

It is very common to specify a position as an offset from some other position using this format. Some examples:

• 1cm below Obstacle.s
• 0.5*linewid left of C0.w
• dist(C2,C3) heading 30 from C2