# Technical Drawing - Interpenetration - Line Penetration

First of all we are going to break Interpenetration down into its most basic element, where we find the point where a line penetrates a flat surface or plane.  Below is the dimensioned diagram you need to draw in order to practice this exercise.

Generally it is important in Technical Drawing to label points of importance, but in Interpenetration it is doubly important.  This will become more noticeable as the drawings become more complicated but it is good practice to start the way you mean to continue.
From the Plan and Elevation you should be able to see that you have a plane surface at an angle to the Vertical Plane (VP).  You are told a line L, 50mm above the Horizontal Plane (HP) and 45mm out from the VP penetrates the plane surface.  You are asked to find where this penetration occurs.

You cannot see where the line penetrates the plane in the Elevation, but in the Plan you can see where the penetration occurs.  This leads us to the solution of the problem.

Remember that when you are setting up this question draw all of your lines very lightly and label the points.  Below you can see how to complete the question.
Set up your drawing according to the given dimensions, remembering to label your points and draw lightly.
In the Plan you can see where the line intersects with the plane.  Project this point onto the line in the Elevation.
You should be able to see from the Elevation and Plan where the line is behind the plane from the direction that you are looking at it.  You do not need to draw in hidden detail unless you are asked to do so in your question, but we do it here for clarity.