Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Field Coordinate System page - add image descriptions and other readability fixes #325

Open
wants to merge 4 commits into
base: main
Choose a base branch
from
Open

Field Coordinate System page - add image descriptions and other readability fixes #325

Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
5798bdc
add image descriptions and other readability fixes
acharraggi Nov 12, 2024
b63b782
fix text descriptions of one image, add Glossary, adjust capitalized …
acharraggi Nov 15, 2024
f4d45a2
more changes and I think a better approach to long descriptions
acharraggi Nov 23, 2024
5f58c35
fix spelling mistake
acharraggi Nov 23, 2024
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
226 changes: 166 additions & 60 deletions ...rce/game_specific_resources/field_coordinate_system/field-coordinate-system.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,117 +1,223 @@
*FIRST* Tech Challenge Field “Coordinate System" Definition
===========================================================
*FIRST* Tech Challenge Field Coordinate System Definition
=========================================================

.. meta::
:description: This document defines the Field Coordinate System which can be used to specify position on the playing field.


Summary: The *FIRST* Tech Challenge Field Coordinate System is a Cartesian Coordinate System of three dimensions.
The X and Y axes will refer to a position on the Field and the Z axis a height above the Field.

.. contents:: In This Article:
:local:
:depth: 1
:backlinks: none

Scope
-----

This document defines the “standard” Coordinate System (orthogonal axes)
definition for a *FIRST* Tech Challenge playing field. This definition can be
This document defines the Field Coordinate System
for a *FIRST* Tech Challenge playing Field. This definition can be
used for consistent field-centric navigation, target localization and path
planning.

Reference frame
Reference Frame
---------------

The reference frame for this definition is the field perimeter wall, adjacent
to the RED Alliance Station (known here as the: RED WALL). The definition is
from the perspective of a person, standing outside the field, in the center of
RED WALL, looking towards the center of the field.

Caveat: If the Red Alliance Station is ever adjacent to two perimeter walls,
the RED WALL will be the one with *most* contact with the Alliance Station. If
the red Alliance Station is ever adjacent to two perimeter walls EQUALLY, then
the most clockwise of the two walls will be considered to be the RED WALL.
The reference frame for this definition is the Field perimeter wall, adjacent
to the red Alliance Area, known here after as the Red Wall. The definition is
from the perspective of a person, standing outside the Field, in the center of
Red Wall, looking towards the center of the Field.

.. note::
If the red Alliance Area is ever adjacent to two perimeter walls,
the Red Wall will be the one with *most* contact with the Alliance Area. If
the red Alliance Area is ever adjacent to two perimeter walls *equally*, then
the most clockwise of the two walls will be considered to be the Red Wall.

Coordinate System
-----------------

The Field Coordinate System is a Cartesian Coordinate System of three dimensions.
X and Y will refer to a position on the field.
Z will refer to a height above the field.
You may use any length measure as long as the same measure is used for all three axes.
The coordinates are ordered (X, Y, Z).
Example: coordinate position (10, -10, 0) has X = 10, Y = -10 and Z = 0.

Origin
^^^^^^

The 0,0,0 origin of the *FIRST* Tech Challenge coordinate system is the point
in the center of the field, equidistant from all 4 perimeter walls (where the
in the center of the Field, equidistant from all 4 perimeter walls (where the
four center tiles meet). The origin point rests on the top surface of the floor
mat.

X Axis
^^^^^^

Looking at the origin from the RED WALL, the X axis extends through the origin
point and runs to the right and left, parallel with the RED WALL. The X axis
Looking at the origin from the Red Wall, the X axis extends through the origin
point and runs to the right and left, parallel with the Red Wall. The X axis
values increase to the right.

Y Axis
^^^^^^

Looking at the origin from the RED WALL, the Y axis extends through the origin
point and runs out and in, perpendicular to the RED WALL. Increasing Y values
run out (away) from the RED WALL.
Looking at the origin from the Red Wall, the Y axis extends through the origin
point and runs out and in, perpendicular to the Red Wall. Increasing Y values
run out (away) from the Red Wall.

Z Axis
^^^^^^

Looking at the origin from the RED WALL, the Z axis extends through the origin
Looking at the origin from the Red Wall, the Z axis extends through the origin
point and runs up and down in a vertical line. Increasing Z values extend
upwards.

Rotation about Axes
Rotation About Axes
^^^^^^^^^^^^^^^^^^^

When considering rotations about an axis, consider yourself looking down the
(positive) axis of rotation from the positive towards the origin. Positive
rotations are then CCW, and negative rotations CW.

axis from the positive end towards the origin. Positive
rotations are then counterclockwise and negative rotations clockwise.
.. figure:: images/image1.jpg
:width: 35%
:align: center
:alt: Coordinate Axes

Figure 1: Coordinate Axes
:alt:

Rotations about each axis.

An example: consider looking down the positive Z axis towards the origin. This
would be like standing in the middle of the field, looking down. A positive
rotation about Z (i.e. a rotation parallel to the X-Y plane) is then CCW, as
one would normally expect from the usual classic 2D geometry.
Imagine looking down the positive Z axis towards the origin.
This would be like standing in the middle of the Field
looking down at the intersection of the tiles in the very center of the Field.
A positive rotation about the Z axis is then counterclockwise.

Examples
--------

Below are two examples illustrating this Axes definition.
Example: a robot spinning clockwise on the Field is making a negative rotation about the Z axis.

.. note::
Note that in both cases the Red Alliance members are facing out,
along the positive Y axis.
Field Configuration Examples
----------------------------

However, in the “Diamond” field configuration, the X axis is pointing
towards the Blue Alliance, but in the “Square” field configuration
the Y axis is pointing towards the Blue Alliance.
Below are two examples illustrating the Field Coordinate System for different
*FIRST* Tech Challenge Field configurations.

Diamond Field
^^^^^^^^^^^^^

.. figure:: images/image2.jpg
:width: 75%
:align: center
:alt: RES-Q

Figure 2: FIRST Tech Challenge RES-Q game field orientation
:alt:

The *FIRST* RES-Q game Field with X, Y and Z axes shown.

In a diamond Field configuration the two Alliance walls are adjacent.
The Field is rotated 45 degrees such that both Alliances face the audience.
From the audience perspective the Field forms a diamond shape.
The Red Wall will be on the right as seen from the audience,
and the blue wall will be on the left.
The Y axis points across the Field as seen from the Red Wall.
The X axis points to the blue wall.

Square Field
^^^^^^^^^^^^

.. figure:: images/image3.jpg
:width: 75%
:align: center
:alt: Cascade Effect
:alt:

The Cascade Effect game Field with X, Y and Z axes shown.

Figure 3: FIRST Tech Challenge Cascade Effect game field orientation
In a square Field configuration the two Alliances face each other across the Field.
The Field is oriented such that the Red Wall is on the right as seen
from the audience, and the blue wall will be on the left.
The Y axis points across the Field from the Red Wall to the blue wall.
The X axis points away from the audience to the rear of the Field.

.. note::
In both Field configurations the red Alliance is facing out along the positive Y axis,
and the Z axis points up from the center of the Field.

In the diamond Field configuration the X axis is pointing
towards the blue Alliance. In the square Field configuration
the Y axis is pointing towards the blue Alliance.

Coordinate Position Example
---------------------------

Let's consider a robot on the Cascade Effect Field at coordinates
(60, -60, 10) in inches. So X = 60, y = -60, and Z = 10.
Measured in inches, the walls would be about 72 inches from the origin.
Cascade Effect was a Square Field configuration, so
the X axis value of positive 60 would be located close to the rear field wall, away from the audience.
The Y axis value of negative 60 would be located close to the Red Wall, away from the origin.
Together the X and Y values (60, -60) indicate a position in the corner of the Field.
That corner is adjacent to the Red Wall and furthest from the audience.
The Z axis value of 10 places the robot on top of the red
ramp that is in that corner in the Cascade Effect game.

Measured Values
---------------

The following values have been measured from a 2016 competition field. They are
The following metric values have been measured from a 2016 competition Field. They are
representative only, and should not be assumed to be exact, or guaranteed.

- Distance between opposite inside faces of panels: 3580 mm
(if field assembled well: the straps give some adjustment tolerance)
- Distance between opposite inside faces of panels: 3580 mm,
(if the Field is assembled well: the straps give some adjustment tolerance)
- Polycarbonate transparencies have a visible opening height of 255 mm
- The top edge of transparencies is 30 mm from the top of the perimeter
- Total perimeter height is 313 mm
- Tiles are 13mm thick
- Tiles are 13 mm thick

So, for a diamond field configuration, the corner of the field closest to the
So, for a diamond Field configuration, the corner of the Field closest to the
audience, at a height equal to the top of the perimeter wall, would have a
coordinate position of: (-1790, 1790, 300).
coordinate position of: (-1790, 1790, 300) in millimeters.

Additional Information
----------------------

See this Wikipedia article on `Cartesian coordinate system
<https://en.wikipedia.org/wiki/Cartesian_coordinate_system#Three_dimensions>`__
in three dimensions.
The Field Coordinate System rotation convention comes from the
`right hand rule <https://en.wikipedia.org/wiki/Right-hand_rule>`__
of classic geometry.

Robots with a webcam can use :ref:`AprilTags <apriltag/vision_portal/apriltag_intro/apriltag-intro:apriltag introduction>`
to determine where an :ref:`AprilTag is located
<apriltag/understanding_apriltag_detection_values/understanding-apriltag-detection-values:introduction>`
with respect to the robot.
Since AprilTags are in known locations on the field, you can also determine the
:ref:`location of the robot <apriltag/vision_portal/apriltag_localization/apriltag-localization:apriltag localization>`
on the field.

Robots can use an inertial measurement unit (IMU) to measure rotations about axes
with respect to the robot. See :ref:`IMU axes definition. <programming_resources/imu/imu:axes definition>`
The yaw value from the IMU, also known the heading, measures rotation about the Z axis
which points up from the robot.
You can use the IMU to determine which direction a robot is facing.

Glossary
--------

.. glossary::

Alliance
An Alliance is a cooperative of two *FIRST* Tech Challenge teams.
An Alliance in the red Alliance Area is known as the red Alliance,
and an Alliance in the blue Alliance Area is known as the blue Alliance.

Alliance Area
A 120 inch wide by 42 inch deep (304.8 cm by 106.7 cm) by infinitely tall volume
formed by placing Alliance colored tape onto the flooring surface outside of the Field.
The red Alliance Area will have red tape, the blue Alliance Area will have blue tape.
The Alliance Area includes the taped lines.

Cartesian Coordinate System
A Cartesian coordinate system for three-dimensional space consists of an ordered triplet of lines
(the axes) that go through a common point (the origin). The axes are pair-wise perpendicular
(at right-angles to each other). A single unit of measure applies to all three axes.
A point P in space can then be referenced by three numbers which correspond to the three axes.
The Cartesian coordinates of P are those three numbers, in the chosen order.

Field
A square area with walls approximately 12 feet (3.66 meters) long bounded by the
outside edge of the extrusion that frames the walls of the Field perimeter.
The flooring surface of the Field is made of 36 interlocking soft foam tiles.
The nominal size of a tile is 24 inches by 24 inches by 5/8 of an inch.

Loading