This article covers 3D scanning with Artec scanners and a special photogrammetry kit.
A video, illustrating the main processes, while using a photogrammetry kit, is available here.
When to use photogrammetry
Photogrammetry mostly serves to enable extra-precise scanning over large distances (from one to several dozen meters). Its main features are:
- Little or no post-processing
- No manual alignment
- Reliable registration during a 3D-scanning session
- Guaranteed accuracy over big distance (for example, for AICON it is ± (0.05 mm + 0.05 mm/m)
- Artec Studio (version 9.2 or later)
- Artec 3D scanner capable of capturing texture (Eva, MHT, Spider, Space Spider)
- Photogrammetry kit (see a 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.
The 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 glueing 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 from 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 of the captured photos
- Run the AICON Scan Reference software.
- Create a new project.
- Make sure the cross size is entered into 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.
The 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.
3D scanning with photogrammetry in Artec Studio
Before proceeding to 3D scanning, remove the coded targets and the 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 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 eliminate 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 3D-sensors, such as ASUS Xtion Pro Live and Microsoft Kinect?
A: This option is available in Artec Studio 9 and 10, however, in later versions (Artec Studio 11 and 12) "Targets" scanning mode was disabled for 3rd-party sensors, since there might be issues with the 3D accuracy of the sensor itself spoiling the accurate results, provided by the photogrammetry solution.
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