Sketcher ConstrainCoincident/pt

Description
Create a coincident constraint on the selected item

This constraint tool takes two points as its argument and serves to make the two points coincident. (Meaning to make them as-one-point).

In practical terms this constraint tool is useful when there is a break in a profile for example - where two lines end near each other and need to be joined - a coincident constraint on their end-points will close the gap.

Usage
As stated above, this tool takes two arguments - both are points. the command will cause the two points to become coincident and be replaced by a single point.
 * 1) First, it is necessary to highlight two distinct points. ( this will not work if, for example, you attempt to select the start and end point of the same line).
 * 2) Highlighting of a drawing item is achieved by moving the mouse over the item and clicking the left-mouse-button.
 * 3) A highlighted item will change its color to green. (This color can be customized in )
 * 4) Subsequent items can be highlighted by repeating the above procedure(s).  it's unnecessary to hold-down any special key like  to achieve multiple item selection in a drawing.
 * 5) Once you have two points highlighted, you can invoke the command using several methods:
 * 6) * Pressing on the constraint button in the toolbar.
 * 7) * Using the keyboard shortcut.
 * 8) * Using the entry in the top menu.

In order to make two points coincident, FreeCAD must out of necessity move one (or both) of the original points.

General scripting
The constraint can be created from macros and from the python console by using the following command:

where :
 * is a sketch object
 * is the number of the line, that will not move by applying the constraint
 * is the number of the vertex of the line that has to fulfilled the constraint
 * is the number of the line, that will move by applying the constraint
 * is the number of the line, that has to fulfilled the constraint

The main issue by using this function is to identify correctly the line number and the vertex number of the lines you want to process.

The next paragraph will explain you how to identify the numbering of a line and of a vertex of a line.

Identifying the numbering of a line
I have drawn three lines as shown in the following figure.



By moving the cursor of the mouse above the line you can see the line number at the bottom left of the FreeCAD windows, see next figure.



Unfortunately the numbering displayed on the FreeCAD windows start from 1 whereas the numbering of the line used to script start from 0: this means that you have to retrieve one each time you want to refer to a line.

Identifying the numbering of the vertices of a line
The vertices of one line can only have the value 1 or 2. (Note that the vertices numbering does not start from 0, this is because with regards to Constraints 0= Edge hence not a vertex, 1 = starting point vertex, 2 = end point vertex, 3 = midpoint which is not a vertex) The vertices are numbered according to their order of creation. To find out the order of their creation (If you have a lot of lines, you cannot remember which vertex you have created first), you just have to move the cursor of your mouse above the two vertices of one line, see following figure.



If you read e.g. 4 and 5, it means that the vertex 4 will be referenced by using the number 1 in the script command and the vertex 5 will be referenced by using the number 2 in the script command. Etc.

Example
Let us take the previous example of the three lines. The subsequent figure indicates the numbering of each line and their vertices according to the convention for scripting.



The command yields following result:



The command yields following result: