Lidar Camera Calibration API

Introduction

The API requires the client to upload the images, PCD (pcap, csv, and bin are also supported), and configuration for camera setup in a zip file (.zip extension) in the format defined below. The contents of the zip file are called a dataset.

1. The client makes an Upload and calibrate API call, which uploads their files and runs the calibration algorithm on the images and lidar files for the given configuration.

2. The calibration process is completed without errors if the Upload and calibrate API call response contains dataset_id, extrinsic_camera_coordinate_system, extrinsic_parameters, error_stats, and projected_images.

3. The client can call the Get Extrinsic Parameters API using the dataset_id obtained from the Upload and calibrate API. This API responds with dataset_id, extrinsic_camera_coordinate_system, extrinsic_parameters, error_stats, and projected_images.

Folder Structure

We require image and lidar frame pairs from the camera and lidar for a given calibration.

1. Place the images captured from the camera in a folder.

2. Place the Lidar data captured from the LiDAR in a folder.

3. config.json contains configuration details of the calibration (intrinsic parameters, calibration name, etc.)

Note: Folder structure is optional. Users can place all files in the main directory and zip it.

All fles in the main direcory

Sub folder structure

Contents of the Camera folder

Contents of the LiDAR folder

Note

1. The names of the folders and the images shown here are for demonstration purposes. Users should avoid using space in the folder, lidar, and image filenames.

2. The name of the JSON file should be config.json (case sensitive)

config.json for checkerboard

{
    "calibration_name": "Lidar camera calibration",
    "calibration_type": "lidar_camera_calibration",
    "calibration_group_id": "xxxxxxxxxxxxxxxxxx",
    "multi_target": false,
    "max_correspondence": 0.05,
    "deep_optimization": false,
    "deep_optimization_approach": "custom_ransac",
    "is_lidar_inverted": false,
    "get_initial_estimates_from_lidar_autodetection": true,
    "mapping_pair_to_use_for_initial_estimates": 0,
    "target_matching_the_chosen_board": "0",
    "board_to_chose_from_left": 0,
    "lidar":
    {
        "name": "lidar"
    },
    "extrinsic_camera_coordinate_system": "OPTICAL",
    "intrinsics":
    {
        "camera_name": "camera name",
        "fx": 4809.13303863791,
        "fy": 4804.6573641098275,
        "cx": 1994.0408528062305,
        "cy": 1441.0395643417517,
        "k1": -0.03563526645635081,
        "k2": 0.2338404159941449,
        "k3": -1.3671429904044254,
        "k4": 0,
        "k5": 0,
        "k6": 0,
        "p1": -0.002478228973939787,
        "p2": -0.0026861612981927407,
        "distortion_enabled": false,
        "lens_model": "pinhole"
    },
    "targets":
    {
        "0":
        {
            "horizontal_corners": 7,
            "vertical_corners": 8,
            "type": "checkerboard",
            "square_size": 0.12,
            "padding_right": 0.343,
            "padding_left": 0.22,
            "padding_top": 0.22,
            "padding_bottom": 0.22,
            "on_ground": false,
            "tilted": true,
            "ignore_top_edge": true
        }
    },
    "data":
    {
        "mappings":
        [
            [
                "camera/1.png",
                "lidar/1.pcd"
            ],
            [
                "camera/2.png",
                "lidar/2.pcd"
            ],
            [
                "camera/3.png",
                "lidar/3.pcd"
            ],
            [
                "camera/4.png",
                "lidar/4.pcd"
            ],
            [
                "camera/5.png",
                "lidar/5.pcd"
            ],
            [
                "camera/6.png",
                "lidar/6.pcd"
            ]
        ]
    },
    "extrinsic_params_initial_estimates":
    {
        "roll": -91.22985012342338,
        "pitch": -1.8101400401363152,
        "yaw": -87.84825901836496,
        "px": 0.06356787067597357,
        "py": -0.28854421270970754,
        "pz": -0.015338954542810408
    }
}

Sample config.json

2KB

config.json

config.json for charucoboard

{
    "calibration_name": "Lidar camera calibration",
    "calibration_type": "lidar_camera_calibration",
    "calibration_group_id": "xxxxxxxxxxxxxxxxxx",
    "multi_target": false,
    "max_correspondence": 0.05,
    "deep_optimization": false,
    "deep_optimization_approach": "custom_ransac",
    "is_lidar_inverted": false,
    "get_initial_estimates_from_lidar_autodetection": true,
    "mapping_pair_to_use_for_initial_estimates": 0,
    "target_matching_the_chosen_board": "0",
    "board_to_chose_from_left": 0,
    "lidar":
    {
        "name": "lidar"
    },
    "extrinsic_camera_coordinate_system": "OPTICAL",
    "intrinsics":
    {
        "camera_name": "camera name",
        "fx": 4809.13303863791,
        "fy": 4804.6573641098275,
        "cx": 1994.0408528062305,
        "cy": 1441.0395643417517,
        "k1": -0.03563526645635081,
        "k2": 0.2338404159941449,
        "k3": -1.3671429904044254,
        "k4": 0,
        "k5": 0,
        "k6": 0,
        "p1": -0.002478228973939787,
        "p2": -0.0026861612981927407,
        "distortion_enabled": false,
        "lens_model": "pinhole"
    },
    "targets":
    {
        "0":
        {
            "rows": 14,
            "columns": 14,
            "type": "charucoboard",
            "square_size": 0.08708571428,
            "marker_size": 0.06966857142,
            "dictionary": "5X5",
            "padding_right": 0,
            "padding_left": 0,
            "padding_top": 0,
            "padding_bottom": 0,
            "on_ground": true,
            "tilted": false,
            "ignore_top_edge": true
        },
        "1":
        {
            "rows": 13,
            "columns": 13,
            "type": "charucoboard",
            "square_size": 0.09378461538,
            "marker_size": 0.0750276923,
            "dictionary": "6X6",
            "padding_right": 0,
            "padding_left": 0,
            "padding_top": 0,
            "padding_bottom": 0,
            "on_ground": true,
            "tilted": false,
            "ignore_top_edge": true
        },
        "2":
        {
            "rows": 12,
            "columns": 12,
            "type": "charucoboard",
            "square_size": 0.1016,
            "marker_size": 0.08128,
            "dictionary": "7X7",
            "padding_right": 0,
            "padding_left": 0,
            "padding_top": 0,
            "padding_bottom": 0,
            "on_ground": true,
            "tilted": false,
            "ignore_top_edge": true
        },
        "3":
        {
            "rows": 13,
            "columns": 13,
            "type": "charucoboard",
            "square_size": 0.09378461538,
            "marker_size": 0.0750276923,
            "dictionary": "original",
            "padding_right": 0,
            "padding_left": 0,
            "padding_top": 0,
            "padding_bottom": 0,
            "on_ground": true,
            "tilted": false,
            "ignore_top_edge": true
        }
    },
    "data":
    {
        "mappings":
        [
            [
                "Images/charuco_2_1.jpg",
                "PCDs/charuco_2_1.pcd"
            ],
            [
                "Images/charuco_2_2.jpg",
                "PCDs/charuco_2_2.pcd"
            ],
            [
                "Images/charuco_2_3.jpg",
                "PCDs/charuco_2_3.pcd"
            ]
        ]
    },
    "extrinsic_params_initial_estimates":
    {
        "roll": -91.22985012342338,
        "pitch": -1.8101400401363152,
        "yaw": -87.84825901836496,
        "px": 0.06356787067597357,
        "py": -0.28854421270970754,
        "pz": -0.015338954542810408
    }
}

Sample config.json

4KB

config.json

config.json key description

Key	Type	Description
calibration_name	string	Name of the calibration
calibration_type	string	Non-editable field. Value should be lidar_camera_calibration
calibration_group_id	string	This is an optional key. Provide valid calibration_group_id to add the dataset to calibration group.
get_initial_estimates_from_lidar_autodetection	Boolean	parameter to specify if we want to do autodetection of boards in lidar
mapping_pair_to_use_for_initial_estimates	Integer	Index (0 based) of the mapping data i.e the files pair to use for calculating initial estimates when initial estimates are not provided
target_matching_the_chosen_board	String	String corresponding to the target configuration. The target configuration should be the we want to use for initial estimates calculation
board_to_chose_from_left	number	optional parameter. When we are using "get_initial_estimates_from_lidar_autodetection" as true and the boards multiple boards we are using are of same size then we can specify the board to chose from left that should be considered for initial estimates calculation
multi_target	boolean	true: if multiple targets are used false: if single target is used
max_correspondence	double	Accepted range is from 0 to 1
deep_optimization	Boolean	Performs optimisation for the board edges. true: If tilted = true and deep optimisation is needed false: If deep optimisation is not required or the tilted = false
deep_optimization_approach	string	Accepted values 1. clustering 2. custom_ransac These are two approaches which are used in deep optimization. Users can select any one of these based on there requirement. Default value is clustering
is_lidar_inverted	Boolean	It gives information about whether the point cloud is inverted or non-inverted. By default, we consider the lidar as non-inverted.
lidar_name	string	It is the name given by the client to the lidar. The client can modify it as willed.
extrinsic_camera_coordinate_system	string	Camera coordinate system for extrinsic sensor angles (roll, pitch and yaw). Accepted values OPTICAL ROS_REP_103 NED Default value is OPTICAL
camera_name	string	It is the name given by the client to the camera. The client can modify it as willed.
lens_model	string	Describes the type of lens used by the camera. Accepted values pinhole fisheye
fx	double	Focal length of the cameras in the X-axis. Value in pixels.
fy	double	Focal length of the camera in the Y-axis. Value in pixels.
cx	double	Optical centre of the camera in the X-axis. Value in pixels.
cy	double	Optical centre of the camera in the Y-axis. Value in pixels.
distortion_enabled	boolean	Makes use of distortion coefficients (k1, k2, k3, k4, p1, p2) for the calibration algorithm when set true. Distortion coefficients (k1, k2, k3, k4, p1, p2) are not required if it is false.
k1, k2, k3, k4, p1, p2	double	These are the values for distortion coefficients of the camera lens.Note: If the lens_model is pinhole we require k1, k2, k3, p1, and p2 values (no need of k4) If the lens_model is fisheye then we require the k1, k2, k3, and k4 values. (p1 and p2 are not needed) These parameters are not required if distortion_enabled is false.
targets	Object	It is a dictionary of dictionary with each dictionary having target properties
type	string	Describes the type of target used. Accepted values checkerboard charucoboard
x (or) horizontal_corners	integer	number of horizontaol corners in the checkerboard (this property is needed if the type = checkerboard)
y (or) vertical_corners	integer	number of vertical corners in the checkerboar (this property is needed if the type = checkerboard)
rows	integer	number of horizontaol squares in the charucoboard (this property is needed if the type is charucoboard)
columns	integer	number of vertical squares in the charucoboard (this property is needed if the type is charcuboard)
square_size	double	Size of each square in meters
marker_size	double	The size of marker in a charucoboard in meters ( Normally it is 0.8 times of square size ) (this property is needed if the type is charucoboard)
dictionary	string	It is the string that defines the charuco dictionary of the target. We support 5X5 6X6 7X7 original This property is needed if the type is charucoboard
padding_right	double	padding to the right of the board
padding_left	double	padding to the left of the board
padding_top	double	padding to the top of the board
padding_bottom	double	padding to the bottom of the board
on_ground	Boolean	true: if the board is kept on ground false: if the board is not on the ground
tilted	Boolean	true: if the board is tilted false: if the board is not tilted
ignore_top_edge	Boolean	This is a field to improve the accuracy of deep optimization. If top part of the board is missing in the lidar frame, provide this flag as true else give it as false. By default false is taken
data	Object	It stores the data related to mapping of the camera and the lidar files
mappings	List of lists	It is a list of lists, where each sub-list is a tuple containing names of the image and pcd paired together. Note: The first element in the tuple should be the image path The second element in the tuple should be the lidar frame path from the lidar The client can name their image and lidar frame as they want, but they must have the same name in the mapping list and be present in the provided path
extrinsic_params_initial_estimates	Object with all values as double	The estimated extrinsic parameters which will be optimized during calibration process. All values are required. roll pitch yaw px py pz
extrinsic_params_tolerance	Object with all values as double	Constraints on the range of extrinsic parameters. All values are optional. 1. px_min 2. px_max 3. py_min 4. py_max 5. pz_min 6. pz_max 7. roll_min 8. roll_max 9. pitch_min 10. pitch_max 11. yaw_min 12. yaw_max If any constraint is given, it is required that the initial estimate (extrinsic_params_initial_estimates) be within the min and max bounds. In addition, min values must be always <= max values.

Quickstart

Before invoking the APIs, the client must obtain the clientId and auth token from Deepen AI. If you are a calibration admin, you can create different Access Tokens using the UI and use those instead. clientId is part of the path parameters in most API calls, and the auth token should be prefixed with “Bearer“ and passed to the ‘Authorization’ header in all API requests. How to get Access Tokens can be found on the following link: Access token for APIs

Upload file and calibrate

This POST api call sends a zip file to the server and runs the calibration algorithm. Returns dataset_id, extrinsic_camera_coordinate_system, extrinsic parameters, error_stats, and projected_images to the user as the response.

https://tools.calibrate.deepen.ai/api/v2/external/clients/{clientId}/calibration_dataset

Request

Path parameters

Parameter name	Parameter type	Description
clientId	string	ClientId obtained from Deepen AI

Body

Key	Value	Description
file	.zip file	Zip file containing config and images in a suitable format

Response

{
    "dataset_id": "XXXXXXXXXXXXXXXXX",
    "calibration_algorithm_version": "XXXXXXXXXXXXXXXXX",
    "extrinsic_camera_coordinate_system": "OPTICAL",
    "extrinsic_parameters": {
        "roll": -90.47755237974575,
        "pitch": -0.38434110269976385,
        "yaw": -87.95967045393508,
        "px": 0.06958801619530329,
        "py": -0.28251980028661544,
        "pz": -0.010306058948604074
    },
    "error_stats": {
        "translation_error": 0.04085960836364045,
        "plane_translation_error": 0.00832952204,
        "rotation_error": 0.7512576778920595,
        "reprojection_error": 27.18615944133744
    },
    "projected_images": "XXXXXXXXXXurl_to_download_projected_imagesXXXXXX"
    
}

Key	Description
dataset_id	A unique value to identify the dataset. dataset_id can be used to retrieve the extrinsic parameters.
calibration_algorithm_version	The version of the algorithm used to calculate extrinsic parameters. This value can be used to map extrinsic parameters to a specific algorithm version.
extrinsic_camera_coordinate_system	Camera coordinate system for extrinsic sensor angles (roll, pitch, and yaw).
extrinsic_parameters	roll, pitch, and yaw are given in degrees and px, py, and pz are given in meters.
error_stats	translation_error: Mean of difference between the centroid of points of checkerboard/charucoboard in the LiDAR and the projected corners in 3-D from an image plane_translation_error: Mean of the Euclidean distance between the centroid of projected corners in 3-D from an image and plane of the checkerboard/charucoboard in the LiDAR rotation_error: Mean of difference between the normals of the checkerboard/charucoboard in the point cloud and the projected corners in 3-D from an image reprojection_error: Mean of difference between the centroid of image corners and projected lidar checkerboard/charucoboard points on the image in 3-D
projected_images	This is a signed URL to download the images with corresponding lidar points projected on them using the extrinsics obtained at the end of the calibration. This URL has an expiry of 7 days from the moment it is generated. The image below shows an example image for this projection.

Image which has the projected points from the lidar frame onto the image frame using the extrinsics obtained from the calibration

Get Extrinsic Parameters

This GET api call returns dataset_id, extrinsic_camera_coordinate_system, extrinsic parameters, error_stats, and projected_images to the user as the response.

https://tools.calibrate.deepen.ai/api/v2/external/datasets/{dataset_id}/extrinsic_parameters

https://tools.calibrate.deepen.ai/api/v2/external/datasets/{dataset_id}/extrinsic_parameters/{extrinsic_camera_coordinate_system}

Request

Path parameters

Parameter name	Parameter type	Description
dataset_id	string	dataset_id obtained from the response of Upload file and calibrate API.
extrinsic_camera_coordinate_system	string	Camera coordinate system for extrinsic sensor angles (roll, pitch and yaw). Accepted values OPTICAL ROS_REP_103 NED Default value is OPTICAL

Response

{
    "dataset_id": "XXXXXXXXXXXXXXXXX",
    "calibration_algorithm_version": "XXXXXXXXXXXXXXXXX",
    "extrinsic_camera_coordinate_system": "OPTICAL",
    "extrinsic_parameters": {
        "roll": -90.47755237974575,
        "pitch": -0.38434110269976385,
        "yaw": -87.95967045393508,
        "px": 0.06958801619530329,
        "py": -0.28251980028661544,
        "pz": -0.010306058948604074
    },
    "error_stats": {
        "translation_error": 0.04085960836364045,
        "plane_translation_error": 0.00832952204,
        "rotation_error": 0.7512576778920595,
        "reprojection_error": 27.18615944133744
    },
    "projected_images": "XXXXXXXXXXurl_to_download_projected_imagesXXXXXX"
}

Key	Description
dataset_id	A unique value to identify the dataset. dataset_id can be used to retrieve the extrinsic parameters.
calibration_algorithm_version	The version of the algorithm used to calculate extrinsic parameters. This value can be used to map extrinsic parameters to a specific algorithm version.
extrinsic_camera_coordinate_system	Camera coordinate system for extrinsic sensor angles (roll, pitch, and yaw).
extrinsic_parameters	roll, pitch, and yaw are given in degrees and px, py, and pz are given in meters.
error_stats	translation_error: Mean of difference between the centroid of points of checkerboard/charucoboard in the LiDAR and the projected corners in 3-D from an image plane_translation_error: Mean of the Euclidean distance between the centroid of projected corners in 3-D from an image and plane of the checkerboard/charucoboard in the LiDAR rotation_error: Mean of difference between the normals of the checkerboard/charucoboard in the point cloud and the projected corners in 3-D from an image reprojection_error: Mean of difference between the centroid of image corners and projected lidar checkerboard/charucoboard points on the image in 3-D
projected_images	This is a signed URL to download the images with corresponding lidar points projected on them using the extrinsics obtained at the end of the calibration.