Calculate the distance between two 3D objects (Camera, Axis) in Nuke. 3D distance needs the two objects, 2D distance also needs a Camera input and an optional format when different from the root format.

CS_DistanceBetween.tcl

set cut_paste_input [stack 0]
version 10.5 v3
push $cut_paste_input
Group {
 name CS_DistanceBetween1
 tile_color 0x9c0000ff
 label "Distance2D: \[value Distance2D]\nDistance3D: \[value Distance3D]"
 selected true
 xpos 290
 ypos -95
 addUserKnob {20 CS_DistanceBetween}
 addUserKnob {41 ObjectAPosition l "Object A Position" T Reconcile3DA.output}
 addUserKnob {41 ObjectBPosition l "Object B Position" T Reconcile3DB.output}
 addUserKnob {7 Distance2D t "Distance between ObjectA and ObjectB in 2D space (X and Y)." R 0 100}
 Distance2D {{"sqrt( pow2( Reconcile3DB.output.x - Reconcile3DA.output.x ) + pow2( Reconcile3DB.output.y - Reconcile3DA.output.y ) )"}}
 addUserKnob {7 Distance3D t "Distance between ObjectA and ObjectB in 3D space (X, Y and Z)." R 0 100}
 Distance3D {{"sqrt( pow2( AxisB.world_matrix.3 - AxisA.world_matrix.3 ) + pow2( AxisB.world_matrix.7 - AxisA.world_matrix.7 ) + pow2( AxisB.world_matrix.11 - AxisA.world_matrix.11 ) )"}}
 addUserKnob {22 UpdateLabel t "Updates the label of this node in the Node Graph. This could be necessary when values are linked via expressions. The update is executed automatically on frame changes." T nuke.updateUI() +STARTLINE}
 addUserKnob {26 ""}
 addUserKnob {26 Creator l "" +STARTLINE T "CS_DistanceBetween v1.1 by Christian Schulze - www.christian-schulze.eu"}
}
 Output {
  inputs 0
  name Output1
  xpos -40
  ypos 302
 }
 Input {
  inputs 0
  name ObjectA
  xpos -260
  ypos 86
  number 1
 }
 Axis2 {
  name AxisA
  xpos -250
  ypos 162
 }
 Input {
  inputs 0
  name InputCam
  xpos -150
  ypos 86
  number 2
 }
set Ndce4f800 [stack 0]
 Input {
  inputs 0
  name InputFormat
  xpos 70
  ypos 86
  number 3
 }
set Ndce4f400 [stack 0]
 Reconcile3D {
  inputs 3
  calc_output true
  name Reconcile3DA
  xpos -150
  ypos 176
 }
 Input {
  inputs 0
  name ObjectB
  xpos 180
  ypos 86
 }
 Axis2 {
  name AxisB
  xpos 190
  ypos 162
 }
push $Ndce4f800
push $Ndce4f400
 Reconcile3D {
  inputs 3
  calc_output true
  name Reconcile3DB
  selected true
  xpos 70
  ypos 176
 }
end_group