Some months ago, MESA was asked to do some as-built drawings for a customer that had us do the original assembly modeling in Inventor. I saw this as a great opportunity to bring together the original model with a ReCap point cloud. Through the process, I learned a few valuable lessons about the process and feel this is a good opportunity to share those lessons.
The first step in the process was to take the photos of the equipment. From all my previous work with ReCap I knew that we wanted to take pictures from around the model, making a ring around the equipment, and pictures from different elevations. One of my co-workers, Mike has a nice camera, so we got a ladder and started photographing the model. We knew that ReCap has a limitation of 250 photos per model, and by chance, Mike took exactly 250 photos.
I took the photos and began creating the model. I used a few measurements to ensure that the model would be scaled properly. Looking at the point cloud from my first attempt, I was surprised that it seemed to have an issue with the back of the machine. After thinking about it for a while, I realized why. The decal on the front and back of the tank are the same, and since the tank is symmetrical, ReCap interpreted some of the photos of the back of the tank as being from the front.
My remedy to this was to split the photos into two groups, Group #1 was photos from the front and the two ends. Group #2 was photos of the back and two ends. So, then I was able to create point clouds for both portions of the equipment. At that point, I had two options, create one ReCap project bringing in both the front and back point clouds, or bring both into the Inventor model. I chose to bring them both into ReCap because that gave me the ability to create regions of points, which can be used to turn off unnecessary points.
Once all of that was done, I was ready to bring the point cloud into an Inventor assembly I created for the purpose of comparing the Inventor model to the point cloud. I discovered something when I did this that I did not anticipate. Even though, I had the model scaled properly and had the origin where I wanted, my point cloud was not flush to the origin the way I had hoped. There are ways to tweak the point clouds orientation in Inventor, but the method of doing this was tedious to say the least. I could perform some measurements to see how many degrees I needed to rotate the point cloud around its origin, then repeat for another axis, only to find that the previous axis would need adjusted.
The solution to this was to take better control of the orientation of the point cloud when registering points in the photos. Instead of just assigning an origin point, I could give coordinates to the four corners of the equipment. Doing this will improve the orientation of the point cloud and provide the scaling information for the point cloud as well.
With all of these lessons learned, I was able to develop a good workflow for bringing all of this together.
Here is a Screencast that shows how to register the photos with the coordinate points.
Here is a Screencast that shows how to use Regions to clean up the data before bringing it into Inventor.
Here is a Screencast that shows how to bring the Inventor model together with the point cloud.
The workflow to perform the As-Built verification is not difficult, but if you follow this process, it will become easier.
