Package edu.wpi.first.apriltag

Class AprilTagFieldLayout

java.lang.Object

edu.wpi.first.apriltag.AprilTagFieldLayout

public class AprilTagFieldLayout
extends Object

Class for representing a layout of AprilTags on a field and reading them from a JSON format.

The JSON format contains two top-level objects, "tags" and "field". The "tags" object is a list of all AprilTags contained within a layout. Each AprilTag serializes to a JSON object containing an ID and a Pose3d. The "field" object is a descriptor of the size of the field in meters with "width" and "length" values. This is to account for arbitrary field sizes when transforming the poses.

Pose3ds in the JSON are measured using the normal FRC coordinate system, NWU with the origin at the bottom-right corner of the blue alliance wall. setOrigin(OriginPosition) can be used to change the poses returned from getTagPose(int) to be from the perspective of a specific alliance.

Tag poses represent the center of the tag, with a zero rotation representing a tag that is upright and facing away from the (blue) alliance wall (that is, towards the opposing alliance).

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	AprilTagFieldLayout.OriginPosition

Constructor Summary

Constructors

Constructor	Description
AprilTagFieldLayout(String path)	Construct a new AprilTagFieldLayout with values imported from a JSON file.
AprilTagFieldLayout(Path path)	Construct a new AprilTagFieldLayout with values imported from a JSON file.
AprilTagFieldLayout(List<AprilTag> apriltags, double fieldLength, double fieldWidth)	Construct a new AprilTagFieldLayout from a list of AprilTag objects.

Method Summary

Modifier and Type	Method	Description
boolean	equals(Object obj)
double	getFieldLength()	Returns the length of the field the layout is representing in meters.
double	getFieldWidth()	Returns the length of the field the layout is representing in meters.
Pose3d	getOrigin()	Returns the origin used for tag pose transformation.
Optional<Pose3d>	getTagPose(int ID)	Gets an AprilTag pose by its ID.
List<AprilTag>	getTags()	Returns a List of the AprilTags used in this layout.
int	hashCode()
static AprilTagFieldLayout	loadFromResource(String resourcePath)	Deserializes a field layout from a resource within a internal jar file.
void	serialize(String path)	Serializes a AprilTagFieldLayout to a JSON file.
void	serialize(Path path)	Serializes a AprilTagFieldLayout to a JSON file.
void	setOrigin(AprilTagFieldLayout.OriginPosition origin)	Sets the origin based on a predefined enumeration of coordinate frame origins.
void	setOrigin(Pose3d origin)	Sets the origin for tag pose transformation.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Details

AprilTagFieldLayout

public AprilTagFieldLayout(String path) throws IOException

Construct a new AprilTagFieldLayout with values imported from a JSON file.

Parameters:

path - Path of the JSON file to import from.

Throws:

IOException - If reading from the file fails.

AprilTagFieldLayout

public AprilTagFieldLayout(Path path) throws IOException

Construct a new AprilTagFieldLayout with values imported from a JSON file.

Parameters:

path - Path of the JSON file to import from.

Throws:

IOException - If reading from the file fails.

AprilTagFieldLayout

public AprilTagFieldLayout(List<AprilTag> apriltags, double fieldLength, double fieldWidth)

Construct a new AprilTagFieldLayout from a list of AprilTag objects.

Parameters:

apriltags - List of AprilTag.

fieldLength - Length of the field the layout is representing in meters.

fieldWidth - Width of the field the layout is representing in meters.

Method Details

getTags

public List<AprilTag> getTags()

Returns a List of the AprilTags used in this layout.

Returns:

The AprilTags used in this layout.

getFieldLength

public double getFieldLength()

Returns the length of the field the layout is representing in meters.

Returns:

length, in meters

getFieldWidth

public double getFieldWidth()

Returns the length of the field the layout is representing in meters.

Returns:

width, in meters

setOrigin

public final void setOrigin(AprilTagFieldLayout.OriginPosition origin)

Sets the origin based on a predefined enumeration of coordinate frame origins. The origins are calculated from the field dimensions.

This transforms the Pose3d objects returned by getTagPose(int) to return the correct pose relative to a predefined coordinate frame.

Parameters:

origin - The predefined origin

setOrigin

public final void setOrigin(Pose3d origin)

Sets the origin for tag pose transformation.

This transforms the Pose3d objects returned by getTagPose(int) to return the correct pose relative to the provided origin.

Parameters:

origin - The new origin for tag transformations

getOrigin

public Pose3d getOrigin()

Returns the origin used for tag pose transformation.

Returns:

the origin

getTagPose

public Optional<Pose3d> getTagPose(int ID)

Gets an AprilTag pose by its ID.

Parameters:

ID - The ID of the tag.

Returns:

The pose corresponding to the ID passed in or an empty optional if a tag with that ID was not found.

serialize

public void serialize(String path) throws IOException

Serializes a AprilTagFieldLayout to a JSON file.

Parameters:

path - The path to write to.

Throws:

IOException - If writing to the file fails.

serialize

public void serialize(Path path) throws IOException

Serializes a AprilTagFieldLayout to a JSON file.

Parameters:

path - The path to write to.

Throws:

IOException - If writing to the file fails.

loadFromResource

public static AprilTagFieldLayout loadFromResource(String resourcePath) throws IOException

Deserializes a field layout from a resource within a internal jar file.

Users should use AprilTagFields.loadAprilTagLayoutField() to load official layouts and AprilTagFieldLayout(String) for custom layouts.

Parameters:

resourcePath - The absolute path of the resource

Returns:

The deserialized layout

Throws:

IOException - If the resource could not be loaded

equals

public boolean equals(Object obj)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object