Author : Garry Curtis
Exporting X-Y-Z Data
Autocad is a very powerful , complex and versatile computer program that quickly became an industry standard almost 20 years ago . Today we will very briefly touch on one particular aspect of it's current advanced capabilities , importing data in order to build a virtual 3D object directly inside Autocad for visualization purposes .
Obviously the many intricate steps involved in a process this complex and elaborate are far beyond the scope of this simple example overview . However , we can easily walk through the basic steps required to create these virtual objects , starting with the data gathering .
Typically a Laser Scanner Such As These, or , the FARO would be used to gather this type of field data . Laser scanners are incredible machines with abilities to scan and log hundreds of thousands , even millions of data points . The data can then be transferred to a laptop or office computer for visualization and scrutiny .
This technology is used in industrial applications when standard measuring techniques are not possible because of object shape or location . For instance , they are used in the film industry for creating elaborate costumes or makeup that will fit each actor's face or body precisely . A face is scanned and the data sent to the maker of the custom Latex Facial prostheticso that the custom device will fit precisely and comfortably for all actors .
However , for field applications such as Accident Reconstruction a Laser Scanner would be overkill and so Total Stations are the tools of choice . The purpose of this example is simply to show how a person can gather and import field data into Autocad for visualizations . The Total Station we'll use is one of the Leica Reflectorless models . Normally a reflecting prism is required for Total Station usage , but this model has the ability to also shoot fairly accurately without requiring a prism .
The Object - A Hardhat
We'll choose a simple object for this example , a shiny hardhat . The T.S. is stationary of course , and the hardhat will be placed on a table in such a position that we will be able to see it's shape most easily . It will also be 'leveled' so that we are able to scan it one single line pass at a time in a side-to-side sweeping manner .
We'll scan it with parallel lines , from front to back at point intervals of 1/4 inch and lines spaced apart at 1 inch . Because the hardhat is perfectly symmetrical at it's middle point we will not scan both sides (left & right) but will simply mirror one side in Autocad in order to simplify the process .
Each parallel line will be given a label name inside the Leica , such as pass-1 , pass-2 , pass-3 etc . Technically this is not required for object assembly in Autocad but constant labelling is always a good habit in case we need to backtrack and check the data for errors or confirmation .
For instance , we can see in the animation above that part of the hardhat's lower side is missing . Back checking the data clearly revealed that the angle of the beam was a little too steep in that particular area for the Reflectorless Leica . Such shiny and steep areas should be covered with a duller surface such as masking or adhesive tape etc , or simply use a prism to get precise numbers .
Point Cloud Data Gathered - 400 points
Data is gathered and the hundreds of points resides inside the T.S. on it's flashcard in an x-y-z format . We'll turn off the Leica and plug the card into our office workstation . We'll open Autocad and simply import the data points , and save the file to the hard drive in the proper Autocad format . We'll also save the raw Leica data to the drive in a .txt format for backup . Close Autocad and replace the flashcard back to the Leica .
Fire Autocad up and load the points file as a 'Point Cloud' , telling Autocad to make the points visible with markers . The object is difficult to visualize at this point , but select all the points and instruct Autocad to build a 'Mesh' from these data points . Wait a few seconds for that task to complete , then reselect the data points and turn off their visibility in order to clean up our work screen .
Select the 3D mesh and instruct Autocad to smooth the surface . The jagged looking mesh will now look much better , using spline interpolation to smooth any roughness . We are using OpenGL to visualize the hardhat mesh to this point so now let's do a 3D render using lights and shadows to allow our 3D object to look much more realistic .
Autocad allows us to move our screen camera around or rotate the object for easy visualization . If we desire we can also animate the virtual Autocad camera , creating a series of .BMP/.TGA frames and then assemble those frames into a flash animation that can be attached to an e-mail for distribution or uploaded to a web server for remote linking .