Get the Moment of Inertia, Area and Perimeter using Autocad:

This tutorial will teach you how to get the moment of inertia, area and perimeter of a drawing entity in autocad. Ok, well as you might already know not all kinds of drawing objects or entities can be extracted with moment of inertia, area and perimeter. What we are talking about here are closed figures such as rectangles, squares, trapezoids, circles and any irregular shapes that are closed or closed polygons to be specific. However, before can we can get the properties mentioned above these drawing objects must be first converted into regions.

To convert a drawing object into region, do the following: 1. Type "region" in the command prompt. 2. Select the drawing object and press enter. The drawing object should be an autocad region at this time. 3. However, if your drawing object has a hole inside, say a pipe which must be composed of inner and outer circles, you must convert each circle into a region and then subtract the inner circle region from the outer circle region. To do this, type "subtract" in the command prompt, press enter and select first the outer circle and then the inner circle. By this time, you should already have a pipe region. Now, there is still one more important thing that you need to do. You must verify that you have indeed created the pipe region. Point your cursor into the outer circle. If both the outer and inner circles highlight, then you have successfully created a pipe region otherwise you need to start over.
Now that you already have a region, you are now set to get its moment of inertia, area and perimeter. The magical command here is "massprop" which stands for mass properties. Here are the steps:

1. First, you need to get the centroid of the region and then use that property to set the the User Coordinate System (UCS) to zero. Type in "massprop", press enter and select the region on your autocad screen and press enter again. By this time, Autocad will show the properties Area, Centroid (x, y), Perimeter and Moment of Inertia among others in the command prompt. To get a complete view of these properties scroll down the command prompt or adjust the command prompt window. The Area and Perimeter properties are final however the moment of inertia is not.
2. To get the correct moment of inertia, you need to set the origin of the UCS into the current centroid of the region. To do this, get the value of centroid (x,y) you obtained in step 1. Type "ucs", press enter, type "m", press enter and then type in the centroid values in this format x,y ( say 12233.0230,323.9441 ) and press enter. The origin of the UCS should now be at the centroid of your region. Type "massprop", press enter, select the region and press enter again. Autocad command prompt should now show the correct moment of inertia. As a check, if you have done everything right the centroid values you obtain this time must be 0.00,0.00 otherwise you made a mistake in entering the centroid values from step 1 into step 2. If this happens, just start over from step 2.