'ARCore – Session, Frame, Camera and Pose
I'm studying the ARCore References, Develop, make the course from Coursera, and read, understood and learn from the Samples.
But I still missing some definition with some real use examples.
What is a session? Every time that I need a ARCore use I need a session? Session always has a camera connect so I can see and draw/renderer my 3D models in the screen? Can I do this without a Session?
Camera has a getPose and Frame has a GetPose, what are the diferences between they?
I thought about make this questions split but somehow I know that they are all connected. Sessions, CameraAr, Frame and Pose.
Solution 1:[1]
About ArSession
ArSession
is the most crucial element in AR puzzle. Session manages AR system state and handles the session lifecycle. Session class is the main entry point to the ARCore API. This class allows the user to create a session, configure it, start or stop it and, most importantly, receiveArFrames
that allow access toARCamera
image and device Pose.
In order to use ARCore you need an
ArSession
. ARCore doesn't render 3D models (Renderables
). This job is forSceneform
framework.
Code's example:
private Session mSession;
Config config = new Config(mSession);
if (!mSession.isSupported(config)) {
showSnackbarMessage("This phone doesn't support AR", true);
}
mSession.configure(config);
Also Session's configuration can include nested classes:
- Config.AugmentedFaceMode (Selects the behaviour of
Augmented Faces
subsystem) - Config.CloudAnchorMode (The cloud anchor mode in
Config
) - Config.FocusMode (Selects the desired behaviour of the
camera focus
subsystem) - Config.LightEstimationMode (Select the behaviour of the
lighting estimation
subsystem) - Config.PlaneFindingMode (Select the behaviour of the
plane detection
subsystem) - Config.UpdateMode (Selects the behaviour of
update()
)
About Pose
Pose
represents an immutable rigid transformation from one coordinate space to another. As provided from all ARCore APIs, Poses always describe the transformation from object's local coordinate space to the world coordinate space. The transformation is defined using a quaternion rotation about the origin followed by a translation.
Code's example:
float[] position = { 0, 0, -2.2 }; // { x, y, z } position
float[] rotation = { 0, 0, 0, 1 }; // { x, y, z, w } quaternion rotation
Session session = arFragment.getArSceneView().getSession();
Anchor myAnchor = session.createAnchor(new Pose(position, rotation));
About ArCamera
ArCamera
represents a virtual camera, which determines the perspective through which the scene is viewed. If the camera is part of anArSceneView
, then the camera automatically tracks the Camera Pose from ARCore. ArCamera is a long-lived object and the properties of camera are updated every timeSession.update()
is called.Camera
class provides information about the camera that is used to capture images and additional info inside eachArFrame
.
Code's example:
// Shared camera access with ARCore
sharedSession = new Session(this, EnumSet.of(Session.Feature.SHARED_CAMERA))
sharedCamera = sharedSession.getSharedCamera();
cameraId = sharedSession.getCameraConfig().getCameraId();
About ArFrame
When ARCore's understanding of the environment changes, it adjusts its model of the world to keep things consistent. When this happens, the numerical location (coordinates) of the
ARCamera
andARAnchors
can change significantly to maintain appropriate relative positions of the physical locations they represent.These changes mean that everyArFrame
should be considered to be in a completely unique world coordinate space. The numerical coordinates ofARAnchors
and theARCamera
should never be used outside the rendering frame during which they were retrieved.
Every
ArFrame
stores the following info about ARCore's state::
- RGB image itself
- Tracking status
- The pose of the camera relative to the world
- Estimated lighting parameters
- Information on updates to objects (like Point Clouds)
Code's example:
private void onUpdateFrame(FrameTime frameTime) {
Frame frame = arFragment.getArSceneView().getArFrame();
// .............
}
Additionally, you can read this useful post.
Sources
This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.
Source: Stack Overflow
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Solution 1 |