Using multiple QR placement markers in Fologram

If you’re trying to use Fologram for a large scale fabrication or assembly task, it’s important to understand the limitations of the HoloLens accuracy. You can see a video here outlining the accuracy of the HoloLens. Fologram provides ways to compensate for drift in the HoloLens using multiple QR placement markers that you can setup and customize for your own fabrication workflow. The following provides a guide for multiple QR placement markers with Fologram.

Preparing your devices and workspace:

In terms of using Fologram for larger construction tasks like this, there are a few things to consider first to improve the accuracy of the holograms streaming from your HoloLens headset. Most of these you’ll be aware of but just double check to be sure:

  • Prepare your workspace environment. This can have a huge effect on how accurate your holograms are in your headset, and we’ve got a nice checklist on the forum about things to consider, which you can find here. The main takeaways are to avoid moving objects, reflective materials and large open spaces, have some distinguishable features in the environment and remove all Holograms in your device and create a fresh scan of your surroundings (by spending 5 minutes just walking around a space and building up environment data)
  • Wearing the HoloLens correctly. It seems a little silly, but the way you wear your HoloLens can actually have a large effect on what you’re seeing through the glasses.
  • Calibrate the headset for your eyes. The HoloLens 2 automatically asks you to re-calibrate, but if you’re on a HL1 you’ll need to do it manually. Once you’ve calibrated your headset will be assigned an ‘IPD’ value that is related to your own eyes. You can find it in the Device Portal under System > Preferences, and adjust this manually to avoid repeating the calibration app in the future.

How multiple QR placement markers work:

When working on larger scale projects in mixed reality you will quickly notice the HoloLens experiences drift and scaling inaccuracies as you move further away from your anchored origin point. Fologram lets you use multiple QR placement markers over large distances to account for these inaccuracies.

  • Snapping to one Fologram QR placement marker aligns the location, rotation and plane of your hologram to your physical space. This works great for local alignments (no more than 3m), however as you move further from your marker, you will notice drift from the HoloLens and rotational error from your marker being slightly misaligned (a 1 degree misalignment can have huge effects over larger distances)
  • Snapping to multiple Fologram QR placement markers aligns rotation of your model between the last two markers. Fologram draws a vector between the last two markers scanned to align the rotation of your model IF there is no rotational data embedded in the marker (see ‘Creating custom QR placement markers’). This automatically accounts for any slight rotational error from your marker being slightly misaligned.
  • The current location is always aligned to the most recently scanned placement marker. If you move away from the most recently scanned marker, you will begin to experience drift and inaccuracy, in which case you should snap to another close by marker. Always work within 3m of a snapped QR placement marker to minimize drift and inaccuracy.

Creating custom QR placement markers:

Once you’re confident you’ve got these things calibrated nicely, then we can start working through a few methods to get the hologram accurately aligning with multiple QR placement markers. First there are a few things to note when producing and setting up the QR marker in your space:

  • To create a custom QR placement marker in Rhino, use the ‘-FologramQR’ command in Rhino. Choose an origin for your marker and align an X and Y axis. The dash at the start of the command is important, as it will give you two extra options: Axis Correction and Include Rotation.
  • Axis correction automatically detects if your QR marker is on a flat surface (ie. the ground or a wall) and accounts for this by snapping to the vector that sets out this alignment. This means you don’t need to worry about creating completely levelled surfaces for your QR markers to sit on - Fologram automatically accounts for this and levels your QR marker on a plane.
  • Include Rotation gives you the ability to embed or remove rotational data. When working with multiple QR markers, it is recommended you turn this OFF to avoid rotational error resulting from human error when laying out the markers. Your model will automatically align rotation after scanning two QR markers.
  • Larger QR markers are easier to accurately align and are detected more accurately than smaller QR markers. If you are able to, make sure you’re creating and then printing your QR markers on at least an A4 sheet, and preferably A3 if possible. The HoloLens camera will have an easier time taking in the information if it is more visible (ie larger) to the camera, and aligning your QR markers will be significantly more accurate with larger sizes.
  • Space your QR placement markers based on the HoloLens drift. You’ll begin to notice drift in your headset after a couple of meters, so it’s important to have QR markers incrementally spaced to accommodate for this. We recommend having QR markers placed every 3 meters to ensure your holograms are accurate across your workspace.
  • Measure up your site and align your markers to static objects in physical space. Try to place your markers somewhere that allows you to align to a wall/edge (this way you’ll know they’re aligned in physical space correctly).

Using Scale Compensation

As you move away from a snapped QR code, your HoloLens will become less accurate. One way to account for this inaccuracy is to use Fologram’s Scale Compensation tool, which allows you to incrementally adjust the size of your model.

  • Scale Compensation is a slider that can be found at the bottom of the Settings menu in Fologram. Increasing/decreasing the value will adjust the overall scale of your model in Fologram. If you are experiencing inaccuracies over larger distances, you can scale your model accordingly to account for this.

Hints and tips:

Once everything is nicely set up, you can put on the HoloLens and start aligning your model. Here are a few tips for usage:

  • Always snap to the QR placement marker nearest to where you’re currently working/viewing your hologram. If you’re snapped to the origin point of a model and you move 20 meters away, you’ll experience a lot of drift from your headset, so try to constantly be re-snapping to the nearest QR placement marker.