3D Scanning Basics: Merging Scans
Welcome back! So you’ve definitely read my other posts and know the basics of what 3D scanners do and how to get around the need for targeting parts if they’re too small, have too many curved surfaces or features, or you have a large amount of parts so you’ve set up a fixture to help expedite the scanning process. Awesome! Except there’s one big problem to scanning a stationary object without targets on the part which VXelements luckily has a solution for. The problem is you usually can’t scan the entire surface, missing the bottom of the part and maybe some undersides. In this situation, we’ll need to make multiple scans of the same part and merge them together using the aptly named ‘Merge Scans’ tool located in the VXscan module of VX elements.
Lets take this project I worked on for one of my coworkers as an example.
On the left is a picture of the completed and cleaned scan of a knight chess piece. It’s full of detail yet only a few inches tall. Getting targets on this part would be difficult and will cover up a lot of the detail we want to capture.
This means I’ll have to use some alternative targeting techniques as described in my previous blog post here or my coworker Tim’s post here. This can limit what parts of the item my scanner can see and thus what it can measure/digitize. If I had a nice symmetrical part, I could just scan half, trim it up, and then mirror it. However, this part has complex geometry that is asymmetrical. This means I’ll have to get a little creative with my scans. I took scans with the part in three different positions: upright, laying on the left side, and laying on the right as pictured below.
Luckily for us, VXscan can easily merge these scans together. By utilizing the Merge Scans tool we can overlay and combine two or more scans.
Once you have started the tool the toolbar appears on the left side of your screen. At the top there are the alignment options: targets, surface best fit, and global registration. Surface best fit is what I’ve found to be easiest and what I’ll use here. In the item selection it shows the fixed mesh (blue) which is the active scan when you select the Merge Scans tool and the mobile mesh which can be selected from one of the other meshes, in this case the right side (pink) of my knight. You have options to keep the original (fixed) scan or have the merge overwrite this scan and the ending resolution as well as how to perform the pre-alignment. In most cases automatic will work just fine. If you have a lot of repeated geometry it could confuse the software so the very simple manual alignment mode will be necessary. In this mode, all you need is to select three corresponding points on the two meshes so that the algorithm has a good starting point.
Once you hit best fit at the bottom it will give you a preview of your merge. When you hit merge it will actually merge the two together to create a new mesh. This first preview isn’t quite enough because it’s still missing some features on the left side, so before hitting merge I can add another scan and hit best fit again for my final preview that features some of our upright (blue), right (pink), and left (yellow) meshes all overlaying.
All that is left now is to hit merge and TA-DA! We now have a merged scan with the best of our three initial scans.
Just remember, you’ll still need to finalize and clean the mesh in VXmodel.
Application Engineer – 3D Scanners & SOLIDWORKS
Computer Aided Technology, Inc.