Spatial anchors - Mixed Reality (2023)

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A spatial anchor represents an important point in the world that the system tracks over time. Each anchor has an adjustable coordinate system, based on other anchors or frames of reference, to ensure anchored holograms stay precisely in place. Rendering a hologram in an anchor's coordinate system gives you the most precise positioning for that hologram at any given time. This comes at the cost of small adjustments over time to the hologram's position as the system continually moves it back into place based on the real world.

You can also persist and share spatial anchors across application sessions and across devices:

  • By saving local spatial anchors to disk and loading them back later, your application can calculate the same location in the real world across multiple application sessions on a single HoloLens.
  • By using Azure Spatial Anchors to create a cloud anchor, your application can share a spatial anchor across multiple HoloLens, iOS, and Android devices. By having each device render a hologram using the same spatial anchor, users will see the hologram appear at the same place in the real world. This allows for real-time shared experiences.
  • You can also use Azure Spatial Anchors for asynchronous hologram persistence across HoloLens, iOS, and Android devices. By sharing a durable cloud spatial anchor, multiple devices can observe the same persisted hologram over time, even if those devices aren't present together at the same time.

For standing-scale or room-scale experiences for tethered desktop headsets that will stay within a 5-meter diameter, you can typically use the stage frame of reference instead of spatial anchors, which provides you a single coordinate system in which to render all content. However, if your application lets users wander beyond 5 meters in HoloLens, perhaps operating throughout an entire floor of a building, you'll need spatial anchors to keep content stable.

While spatial anchors are great for holograms that should remain fixed in the world, once an anchor is placed, it can't be moved. There are alternatives to anchors that are more appropriate for dynamic holograms that tag along with the user. It's best to position dynamic holograms using a stationary frame of reference (the foundation for Unity's world coordinates) or an attached frame of reference.

Best practices

These spatial anchor guidelines will help you render stable holograms that accurately track the real world.

Create spatial anchors where users place them

Typically, users are the ones explicitly placing spatial anchors.

For example, on HoloLens, an application can intersect the user's gaze ray with the spatial mapping mesh to let the user decide where to place a hologram. When the user taps to place that hologram, create a spatial anchor at the intersection point, and then place the hologram at the origin of that anchor's coordinate system.

Local spatial anchors are easy and performant to create. The system combines internal data if multiple anchors can share their underlying sensor data. We recommend creating a new local spatial anchor for each hologram that a user explicitly places, except in cases outlined below, such as rigid groups of holograms.

Always render anchored holograms within 3 meters of their anchor

Spatial anchors stabilize their coordinate system near the anchor's origin. If you render holograms more than 3 meters from the origin, the holograms might experience noticeable positional errors in proportion to their distance from that origin because of lever-arm effects. This works if the user stands near the anchor, since the hologram is far away from the user, too. In other words, the angular error of the distant hologram will be small. However, if the user walks up to that distant hologram, it will be large in their view, making the lever-arm effects from the faraway anchor origin obvious.

Group holograms that should form a rigid cluster

Multiple holograms can share the same spatial anchor if the application expects those holograms to maintain fixed relationships with one another.

For example, if you're animating a holographic solar system in a room, it's better to tie all of the solar system objects to a single anchor in the center. That way, they'll move smoothly based on each other. In this case, it's the solar system as a whole that is anchored, even though its component parts are moving dynamically around the anchor.

The key caveat to maintain hologram stability is to follow the 3-meter rule above.

Render highly dynamic holograms using the stationary frame of reference instead of a local spatial anchor

If you have a highly dynamic hologram, such as a character walking around a room or a floating UI that follows along the wall near the user, it's best to skip local spatial anchors, and render those holograms directly in the coordinate system provided by the stationary frame of reference. In Unity, you achieve this by placing holograms directly in world coordinates without a WorldAnchor. Holograms in a stationary frame of reference might experience drift when the user is far from the hologram. But this is less likely to be noticeable for dynamic holograms: either the hologram is constantly moving anyway or its motion constantly keeps it close to the user where drift will be minimized.

One interesting case of dynamic holograms is an object that is animating from one anchored coordinate system to another. For example, you might have two castles 10 meters apart, each on their own spatial anchor with one castle firing a cannonball at the other castle. When the cannonball is fired, you can render it at the appropriate location in the stationary frame of reference to coincide with the cannon in the first castle's anchored coordinate system. It can then follow its trajectory in the stationary frame of reference as it flies 10 meters through the air. As the cannonball reaches the other castle, you can move it into the second castle's anchored coordinate system to allow for physics calculations with that castle's rigid bodies.

If you're sharing a highly dynamic hologram across devices, pick some cloud spatial anchor to act as their parent because stationary frames of reference cannot be shared across devices. However, you should ensure either the dynamic hologram or the devices viewing it stay within the anchor's 3-meter radius so the hologram appears stable on all devices.

Avoid creating a grid of spatial anchors

You may be tempted to have your application drop a regular grid of spatial anchors as the user walks around, transitioning dynamic objects from anchor to anchor as they move around. However, this involves more management for your application, without the benefit of the deep sensor data that the system itself maintains internally. For these cases, you'll achieve better results by placing your holograms in the stationary frame of reference as described in the section above.When you're pre-positioning a set of cloud spatial anchors around a static space, consider placing the spatial anchors at the locations of the key holograms the user comes across per the principle above rather than creating an arbitrary grid of anchors. This ensures that you'll get maximum stability for those key holograms.

Release local spatial anchors you no longer need

While a local spatial anchor is active, the system prioritizes keeping the sensor data that is near that anchor. If you're no longer using a spatial anchor, stop accessing its coordinate system. This allows its underlying sensor data to be removed as necessary.

This is especially important for local anchors you've persisted to the spatial anchor store. The sensor data behind these anchors will be kept around permanently to allow your application to find that anchor in future sessions, which reduces the space available to track other anchors. Only persist local anchors that you need to find again in future sessions. We recommend removing them from the store when they're no longer meaningful to the user.

For cloud spatial anchors, your storage can scale as your scenario requires. You can store as many cloud anchors as you need, releasing them when you know that your users won't need the anchor again.

See also

  • Coordinate systems
  • Shared experiences in mixed reality
  • Azure Spatial Anchors
  • Persistence in Unity
  • Spatial anchors in DirectX
  • Case study - Looking through holes in your reality


What is a spatial anchor? ›

What are spatial anchors? Across augmented reality (AR) platforms, "anchors" are a common frame of reference for enabling multiple users to place digital content in the same physical location, where it can be seen on different devices in the same position and orientation relative to the environment.

How do spatial anchors work? ›

Spatial anchors work with the image recorded by the device's camera, using image features and their relative position in 3D space to recognize a real-world location. For this location a corresponding anchor is created in the AR space.

What are Azure spatial anchors? ›

Azure Spatial Anchors is a managed cloud service and developer platform that enables multi-user, spatially aware mixed reality experiences across HoloLens, iOS, and Android devices.

How does HoloLens spatial mapping work? ›

HoloLens blends holograms with your physical world. To do that, HoloLens has to learn about the physical world around you and remember where you place holograms within that space. Over time, the HoloLens builds up a spatial map of the environment that it has seen. HoloLens updates the map as the environment changes.

What are the 3 types of anchors? ›

Modern anchor designs that are extremely stable and able to easily grip on to surfaces are generally derived from three standard designs that have been used from the 10th century onwards. These are the – Fluked, Admiralty and Stockless anchor designs that are often still in use for small crafts and lightweight boats.

What are the four major types of anchors? ›

Anchors can be divided into four big groups: grapnels, plough anchors, patent anchors and stock anchors. the classic admiralty one, have disappeared from boats because of their encumbrance and low manageability.

What are the three main working principles for anchors? ›

​​​​​​​High load-carrying capacities. No expansion forces (ideal for fastenings near the edge) Suitable for anchoring in solid and hollow building materials (hollow building materials require a mesh sleeve)

How many types of anchor systems are there? ›

There are three basic types of anchor systems for fall protection: Designed Fixed Support—load-rated anchors specifically designed and permanently installed for fall protection purposes as an integral part of the building or structure (ex. Roof anchors on high-rise buildings).

What is a sensory anchor? ›

A sensory anchor is a behaviour or repetitive activity. Children with Autism display these anchors as a way of helping their brains organise, calm, soothe and achieve or maintain a regulated state.

What are the three types of roles in Microsoft Azure? ›

Account Administrator, Service Administrator, and Co-Administrator are the three classic subscription administrator roles in Azure.

What is cloud anchors? ›

Cloud Anchors connect real world locations with digital content that anyone can access from compatible mobile devices. Both Android and iOS users can participate in the same experience and return to them again and again, even weeks or months later.

Is Azure Sentinel a SIEM or soar? ›

Microsoft Sentinel is a cloud-native security information and event manager (SIEM) platform that uses built-in AI to help analyse large volumes of data across an enterprise—fast.

What are 3 main features of HoloLens? ›

The HoloLens features an inertial measurement unit (IMU) (which includes an accelerometer, gyroscope, and a magnetometer) four "environment understanding" sensors (two on each side), an energy-efficient depth camera with a 120°×120° angle of view, a 2.4-megapixel photographic video camera, a four-microphone array, and ...

Is HoloLens AR or mixed reality? ›

The Hololens is Microsoft's take on augmented reality, which they call “mixed reality”. Using multiple sensors, advanced optics, and holographic processing that melds seamlessly with its environment, These holograms can be used to display information, blend with the real world, or even simulate a virtual world.

What does spatial mapping do? ›

Spatial mapping provides a detailed representation of real-world surfaces in the environment around the HoloLens, allowing developers to create a convincing mixed reality experience. By merging the real world with the virtual world, an application can make holograms seem real.

What are the five 5 types of anchor? ›

Types of Anchors. We have sorted most of the common anchors into five major categories: The Hook, Plough, Fluke, Claw and Scoop.

What is an anchor in NLP? ›

In NLP, “anchoring” refers to the process of associating an internal response with some external or internal trigger so that the response may be quickly, and sometimes covertly, re-accessed.

What are the two types of anchor? ›

There are two main types of anchors: temporary and permanent. A permanent anchor is called a mooring block and is not easily moved. A temporary anchor can be moved and is carried on the boat. When people talk about anchors, they are usually thinking about temporary anchors.

What are the 8 types of anchor? ›

  • Edgar Schein's Career Anchors. There are eight career anchors themes and has shown that people identify primarily with one or two. ...
  • Technical/Functional. ...
  • General Managerial. ...
  • Autonomy/Independence. ...
  • Security/Stability. ...
  • Entrepreneurial Creativity. ...
  • Service/Dedication to a Cause. ...
  • Pure Challenge.

What is the most common type of anchor? ›

The Bruce, or Claw, remains one of the most popular anchors among recreational boaters in North America. This is our anchor of choice as well. The Bruce was developed in the 70s by the Bruce Anchor Group.

What are some common types of anchors? ›

Let's explore some of the most popular options available for boaters when it comes to anchors.
  • Mushroom Anchor. Very large mushroom anchors are used for moorings or securing buoys. ...
  • Danforth or Fluke Anchor. ...
  • Plow Anchor. ...
  • Claw Anchor. ...
  • Grapnel Anchor. ...
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What are the four steps to anchoring? ›

The Four Steps to Anchoring:
  1. Have the person recall a past vivid experience.
  2. Provide a specific stimulus at the peak (see chart below)
  3. Change the person's state.
  4. Set off the anchor to test.

What is the proper technique for anchoring? ›

Anchoring Your Boat
  1. Select an area to anchor with plenty of room. ...
  2. Head slowly into the wind or current to a position upwind or upcurrent of where you actually want to end up.
  3. When you are at that position, stop the boat and slowly lower the anchor over the bow to the bottom.

What are good anchoring practices? ›

The availability of adequate sea floor. The safety swinging circle of the vessel: A circle with a minimum radius including length of anchor chain and the vessel's Length Over All. The proximity of navigational hazards. An adequate safety distance to the nearest vessels and navigational facilities.

What does an anchor mean spiritually? ›

For most, it symbolizes constant faith, steadfast belief, hope and love. However, it can also denote salvation, unwavering dedication and a firm hope in Christ. That's why you'll see many Christians expressing their faith by wearing anchor cross jewelry.

How Azure spatial anchors work? ›

Azure Spatial Anchors enables developers to work with mixed reality platforms to perceive spaces, designate precise points of interest, and to recall those points of interest from supported devices. These precise points of interest are referred to as Spatial Anchors.

What are the three types of anchors used by the Navy? ›

Anchors used in the Navy today are grouped according to type. The most common types used are stockless anchors, lightweight (LWT) or stock-in- crown anchors, and two-fluke balanced-fluke anchors.

What are the two types of anchor points? ›

Type of Anchor Point: It's essential to understand the two main types of anchor points: fall arrest anchors and abseil anchors. Fall arrest anchors are suitable for use in both fall arrest and fall restraint systems, while abseil anchors are designed specifically for abseil or rope access work.


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