This article covers 3D scanning with Artec scanners and a special photogrammetry kit.
When to use photogrammetry
Photogrammetry mostly serves to enable extra-precise scanning over large distances (from one to several dozen meters).
- Little or no post processing
- No manual alignment
- Reliable registration during scanning
- Guaranteed 50-micron accuracy regardless of object size
- Artec Studio (version 9.2 or later)
- Artec scanner capable of capturing texture (Eva, MHT, Spider, Space Spider)
- Photogrammetry kit (see sample photo below)
- Make sure you have room to move around the object at a distance of 0.5 – 1 m.
- If the object is tall, check whether you can safely capture it from above (for example, using a chair, stepladder, etc).
- Ensure you have enough lighting in the room to capture photos.
Cross and non-coded targets
- Place non-coded targets such that at least 6 targets always appear in the scanner's field of view.
- Avoid gluing targets to object edges or to the highly curved surfaces.
- Place the cross and coded targets on an even surface.
- Depending on the object size, place the cross somewhere visible from most or all points of view.
- When placing the next coded target, make sure non-coded targets, the cross and other coded targets are near it.
- We highly recommend placing some targets at different heights (so not all of them are on one height).
Take all pictures at a distance of 0,5 – 1,5 meters from the targets, the camera flash should be enabled.
- The entire cross should be visible in the first 10-12 photos.
- Every photo should contain as many targets as possible; the angle is important because the pattern on the coded targets should be visible and easy to detect.
- To keep photos clear, avoid moving while taking them. You can not use blurred photos in further post processing.
- Capture the first two photos form the same place, rotating the camera by 90° for the second one.
- For subsequent photos keep moving around the object in a circle taking pictures of the scene at each step.
- Important: every target should appear at least at 10 photos.
- If the cross is partly or completely hidden from certain points, try to capture as many coded targets as possible in one picture.
- You can finish taking pictures once you have made a full circle around the object and captured all the targets (coded and non-coded).
- Important: do not move the targets or cross during the photo session. If they shift by accident, start the process again from the very beginning.
Post processing captured photos
- Run the AICON Scan Reference software.
- Create a new project.
- Make sure the cross size is entered in the software.
- Insert a memory card, when the software prompts you to do so.
- The software will load and post process your photos automatically.
- When data processing is complete, check the results to ensure software correctly recognized all targets in the photos.
- Export the data in an OBC file.
Dimensions of the cross to enter in ScanReference software:
A higher-res version of this picture appears at the end of the article.
Structure of OBC / CSV files
We use the four first columns in the file, which are the following:
1: Target ID (we use values greater than 1 000 for non-coded targets)
2,3,4: Coordinates of the non-coded target
More information and some sample files are available in this article: Structure of OBC / CSV file for photogrammetry
3D scanning with photogrammetry in Artec Studio
Before proceeding to 3D scanning, remove the coded targets and cross from the object. They are unnecessary when scanning.
- Choose the size of the targets in File - Settings - Scan
- Switch to section "Scan", then choose option "Targets" and load the OBC / CSV file.
- Start scanning. Important: at least 6 targets should appear in the scanner's field of view at all times when scanning.
- You can stop the the scanning process at any time - for example, you can stop the scan, move to any other position and resume capturing from there.
- All captured scans are already aligned in a single coordinate system using the known targets coordinates from your file.
- To measure the distance between two points, you need only scan those two points (no need to scan the whole area between them).
- If you use light-reflective targets, you can scan from a greater distance, as Eva can more easily recognize these targets.
Post processing in Artec Studio
- Fine and global registration are not needed (your scans are already registered in the workspace using the targets coordinates).
- Run fusion to combine your raw scans into a 3D model.
- You can change the Remove_targets option in properties of your fusion to ON. In this case, Artec Studio will remove the small geometry of the target from the surface when building the 3D model.
- Before performing texture mapping, select the option Remove targets to elimitane your non-coded targets from the object texture. This feature is available in Artec Studio 10 and later.
- Export your 3D model to the appropriate format using File → Export mesh option.
Q: Can I use any other software besides ScanReference for photogrammetry?
A: Yes, you can use any other program if it can generate OBC/CSV files in the necessary format.
Q: Can I use photogrammetry with sensors such as ASUS Xtion Pro Live and Microsoft Kinect?
A: Yes, but we do not recommend doing so, as the resolution and accuracy of these sensor are usually rather low.
The video about photogrammetry usage is available here.
Still have questions?