AprilTag Map Specification
Limelight's field-space localization feature uses .fmap files to compute a robot pose for use by WPILIB's pose estimators. Our fmap files support maps comprised of different target sizes and different families.
You can use fmaps to define "environments" such as FRC fields, or "objects" such as objects that have several attached AprilTags. To use an fmap, all you need to do is upload it to your Limelight using the interface or the REST upload API
The .fmap file is a JSON file containing a single "fiducial" array. Each entry in the fiducial array has the following structure:
| family | AprilTag/Fiducial family |
| id | Tag ID |
| size | Tag size in mm |
| transform | 4x4 Matrix Transform of the target. Row-Major, SI units. |
| unique | Specifies whether the target is unique in this map or featured multiple times |
In addition, the top-level object has a "type" string specifiying the map type.
| type | Field type e.g. frc, ftc, ftcd (ftc diamond) |
AprilTag Map for FRC 2024 Crescendo - Credit to Kevin Hjelstrom
{
"type": "frc",
"fiducials": [
{
"family": "apriltag3_36h11_classic",
"id": 1,
"size": 165.1,
"transform": [
-0.5,
-0.866025,
0,
6.808597,
0.866025,
-0.5,
0,
-3.859403,
0,
0,
1,
1.355852,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 2,
"size": 165.1,
"transform": [
-0.5,
-0.866025,
0,
7.914259,
0.866025,
-0.5,
0,
-3.221609,
0,
0,
1,
1.355852,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 3,
"size": 165.1,
"transform": [
-1.0,
0,
0,
8.308467,
0,
-1.0,
0,
0.877443,
0,
0,
1,
1.451102,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 4,
"size": 165.1,
"transform": [
-1.0,
0,
0,
8.308467,
0,
-1.0,
0,
1.442593,
0,
0,
1,
1.451102,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 5,
"size": 165.1,
"transform": [
0,
1.0,
0,
6.429883,
-1.0,
0,
0,
4.098925,
0,
0,
1,
1.355852,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 6,
"size": 165.1,
"transform": [
0,
1.0,
0,
-6.429375,
-1.0,
0,
0,
4.098925,
0,
0,
1,
1.355852,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 7,
"size": 165.1,
"transform": [
1.0,
-0.0,
0,
-8.308975,
0.0,
1.0,
0,
1.442593,
0,
0,
1,
1.451102,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 8,
"size": 165.1,
"transform": [
1.0,
-0.0,
0,
-8.308975,
0.0,
1.0,
0,
0.877443,
0,
0,
1,
1.451102,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 9,
"size": 165.1,
"transform": [
0.5,
-0.866025,
0,
-7.914767,
0.866025,
0.5,
0,
-3.221609,
0,
0,
1,
1.355852,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 10,
"size": 165.1,
"transform": [
0.5,
-0.866025,
0,
-6.809359,
0.866025,
0.5,
0,
-3.859403,
0,
0,
1,
1.355852,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 11,
"size": 165.1,
"transform": [
0.5,
0.8660254,
0,
3.633851,
-0.8660254,
0.5,
0,
-0.392049,
0,
0,
1,
1.3208,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 12,
"size": 165.1,
"transform": [
0.5,
-0.866025,
0,
3.633851,
0.866025,
0.5,
0,
0.393065,
0,
0,
1,
1.3208,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 13,
"size": 165.1,
"transform": [
-1.0,
0,
0,
2.949321,
0,
-1.0,
0,
-0.000127,
0,
0,
1,
1.3208,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 14,
"size": 165.1,
"transform": [
1.0,
-0.0,
0,
-2.950083,
0.0,
1.0,
0,
-0.000127,
0,
0,
1,
1.3208,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 15,
"size": 165.1,
"transform": [
-0.5,
-0.866025,
0,
-3.629533,
0.866025,
-0.5,
0,
0.393065,
0,
0,
1,
1.3208,
0,
0,
0,
1
],
"unique": 1
},
{
"family": "apriltag3_36h11_classic",
"id": 16,
"size": 165.1,
"transform": [
-0.5,
0.866025,
0,
-3.629533,
-0.866025,
-0.5,
0,
-0.392049,
0,
0,
1,
1.3208,
0,
0,
0,
1
],
"unique": 1
}
]
}