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.
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.
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.
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.
Place the images captured from the camera in a folder.
Place the Lidar data captured from the LiDAR in a folder.
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.
Note
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.
The name of the JSON file should be
config.json
(case sensitive)
config.json for checkerboard
Sample config.json
config.json for charucoboard
Sample 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
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
|
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:
|
targets | Object | It is a dictionary of dictionary with each dictionary having target properties |
type | string | Describes the type of target used. Accepted values
|
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
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:
|
extrinsic_params_initial_estimates | Object with all values as double | The estimated extrinsic parameters which will be optimised during calibration process.
|
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
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. |
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
Default value is OPTICAL |
Response
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. |
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