Extending lines

In many CAD programs the extending function is wrapped up in the trimming function and the CAD draughter supplies an extra parameter to the function. In AutoCAD it is a separate function.

To convert the first drawing into the second drawing. Two lines need to be extended.
         

You have to take note of a few things.
Each CAD program you use has been written by a team of programmers. A different team!! This causes each program to have a different feel about it, use different words and provide different facilities.
One thing they all have in common. The programmers make judgements as to what is an efficient way of achieving a particular outcome. Some on one team think one thing and some on another team think another think. BUT, at the end of the day the outcome is the same. The object is drawn and both programs hold the same information.

To extend the two lines, the extend function is selected then the two lines are picked.

Any single line has two portions to it one left or below its centre and one to the right or above its centre. The CAD program needs to know which portion of the line to extend. The next clip shows the nodes on a line, indicating the two portions.

The vertical line extends ok because the pick box was placed past midway toward the extendable end.
         

This horizontal attempt fails because the pick box was placed in the wrong portion of the line.
         

Now it extends because the pick box was placed in the correct portion of the line.
         

NOTE: Take care and think about what you are asking the computer to do. Try and give the programmer a chance!! Don't forget, the programmer completed this code a while ago and has never seen what you are attempting to draw. It's just a load of numbers to the computer.