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Scanning with photogrammetry

This article covers 3D scanning with Artec scanners and a special photogrammetry kit.

Here we employ AICON ScanReference when describing the workflow, but you can instead use LINEARIS or any other photogrammetry package that supports non-coded targets.

When to use photogrammetry

Photogrammetry mostly serves to enable extra-precise scanning over large distances (from one to several dozen meters).

Main features:

  • Little or no post processing
  • No manual alignment
  • Reliable registration during scanning
  • Guaranteed 50-micron accuracy regardless of object size

Equipment

  • Artec Studio (version 9.2 or later)
  • Artec scanner capable of capturing texture (Eva, MHT, Spider, Space Spider)
  • Photogrammetry kit (see sample photo below)

Initial preparations

  • 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).

Capturing photos
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

  1. Run the AICON Scan Reference software.
  2. Create a new project.
  3. Make sure the cross size is entered in the software.
  4. Insert a memory card, when the software prompts you to do so.
  5. The software will load and post process your photos automatically.
  6. When data processing is complete, check the results to ensure software correctly recognized all targets in the photos.
  7. Export the data in an OBC file.

Dimensions of the cross to enter in ScanReference software:

Entered values:



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.

  1. Choose the size of the targets in File - Settings - Scan
  2. Switch to section "Scan", then choose option "Targets" and load the OBC / CSV file.
  3. Start scanning. Important: at least 6 targets should appear in the scanner's field of view at all times when scanning.
  4. 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.
  5. All captured scans are already aligned in a single coordinate system using the known targets coordinates from your file.
  6. To measure the distance between two points, you need only scan those two points (no need to scan the whole area between them).
  7. 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

  1. Fine and global registration are not needed (your scans are already registered in the workspace using the targets coordinates).
  2. Run fusion to combine your raw scans into a 3D model.
  3. 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.
  4. 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.
  5. Export your 3D model to the appropriate format using File → Export mesh option.

FAQ

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.

Video

The video about photogrammetry usage is available here.

Still have questions?

We are here to help! If you have any questions or issues, please do not hesitate to contact our team by emailing support@artec-group.com or by clicking on "Ask Support" button on the upper part of the screen. We will always be happy to assist you and will get back to you as soon as we can.