# Tangram Vision Documentation

> Use MetriCal for accurate, precise, and expedient calibration of multimodal sensor suites


## metrical


### calibration_guides

- [IMU Data Capture](/metrical/calibration_guides/camera_imu_cal.md): This file explains IMU calibration with MetriCal, which requires no specific targets since IMUs measure forces and velocities directly, and must be performed alongside camera calibration.
- [Camera ↔ LiDAR Calibration](/metrical/calibration_guides/camera_lidar_cal.md): This file provides a comprehensive guide for calibrating camera-LiDAR sensor pairs using MetriCal, including both combined and staged calibration approaches with circular targets.
- [Calibration Guide Overview](/metrical/calibration_guides/guide_overview.md): This file provides general calibration principles and guidelines that apply to all MetriCal calibration scenarios, including target selection, data quality considerations, and sensor-specific guidance.
- [LiDAR ↔ LiDAR Calibration](/metrical/calibration_guides/lidar_lidar_cal.md): This file provides a guide for calibrating multiple LiDAR sensors together using MetriCal with circle targets and includes a practical example dataset.
- [Multi-Camera Calibration](/metrical/calibration_guides/multi_camera_cal.md): This file provides guidance for multi-camera calibration in MetriCal, covering both combined and staged approaches for calibrating camera intrinsics and extrinsics simultaneously.
- [Single Camera Calibration](/metrical/calibration_guides/single_camera_cal.md): This file provides tips and best practices for single camera calibration using MetriCal, including basic workflows and techniques for seeding larger multi-stage calibrations.

### calibration_models

- [Camera Models](/metrical/calibration_models/cameras.md): This file documents all supported camera intrinsics models in MetriCal, including pinhole, distortion models, and fisheye lenses with their respective parameters and mathematical descriptions.
- [IMU Models](/metrical/calibration_models/imu.md): This file documents all supported IMU intrinsics models in MetriCal for calibrating accelerometer and gyroscope measurements with their mathematical modeling and correction processes.
- [LiDAR Models](/metrical/calibration_models/lidar.md): This file documents the supported LiDAR models in MetriCal, which currently focuses on extrinsics calibration since LiDAR intrinsics are typically reliable from the factory.

### changelog

This file contains the comprehensive release notes and changelogs for MetriCal versions, documenting new features, bug fixes, breaking changes, and version-specific improvements.

- [Releases + Changelogs](/metrical/changelog.md): This file contains the comprehensive release notes and changelogs for MetriCal versions, documenting new features, bug fixes, breaking changes, and version-specific improvements.

### commands

- [Calibrate Mode](/metrical/commands/calibrate.md): This file documents the MetriCal calibrate command, which performs full bundle adjustment calibration of multi-modal sensor systems using pre-recorded data, plex configuration, and object space definitions.
- [Errors & Troubleshooting](/metrical/commands/command_errors.md): This file catalogs MetriCal's error codes and exit codes with descriptions and troubleshooting steps for various operational failures and system issues.
- [MetriCal Commands](/metrical/commands/commands_overview.md): This file provides an overview of all MetriCal commands including init, calibrate, report, display, shape, and their universal options and usage patterns.
- [Completion Mode](/metrical/commands/completion.md): This file describes how to generate shell auto-completion scripts for MetriCal across different shell environments including bash, fish, elvish, powershell, and zsh.
- [Consolidate Object Spaces Mode](/metrical/commands/consolidate_object_spaces.md): This file documents the MetriCal consolidate object spaces command, which combines multiple object spaces into a single unified configuration using object relative extrinsics.
- [Display Mode](/metrical/commands/display.md): This file documents the MetriCal display command, which visualizes calibration results applied to datasets using Rerun for ocular validation of calibration quality.
- [Init Mode](/metrical/commands/init.md): This file documents the MetriCal init command, which creates uncalibrated plex files from datasets by inferring components, spatial constraints, and temporal constraints.
- [Pipeline Mode](/metrical/commands/pipeline.md): This file documents the deprecated MetriCal pipeline command, which allowed running series of MetriCal commands in sequence from JSON configuration files.
- [Report Mode](/metrical/commands/report.md): This file documents the MetriCal report command, which generates comprehensive calibration reports from plex files or calibration output files in human-readable formats.
- [Focus](/metrical/commands/shape/shape_focus.md): This file documents the MetriCal shape focus command, which creates hub-and-spoke plex configurations where all components are spatially connected to one focus component.
- [Lookup Table](/metrical/commands/shape/shape_lut.md): This file documents the MetriCal shape LUT command, which creates pixel-wise lookup tables for single camera distortion correction and image undistortion.
- [Stereo Lookup Table](/metrical/commands/shape/shape_lut_stereo.md): This file documents the MetriCal shape stereo LUT command, which creates pixel-wise lookup tables for stereo camera pair rectification and stereo vision applications.
- [Minimum Spanning Tree](/metrical/commands/shape/shape_mst.md): This file documents the MetriCal shape MST command, which creates a plex containing only the minimum spanning tree of spatial components with optimal covariance connections.
- [Shape Mode](/metrical/commands/shape/shape_overview.md): This file provides an overview of MetriCal's shape command, which transforms plex files into various useful output formats for practical deployment and system integration.
- [Tabular](/metrical/commands/shape/shape_tabular.md): This file documents the MetriCal shape tabular command, which exports intrinsic and extrinsic calibration data from plex files in simplified table-based CSV formats.
- [URDF](/metrical/commands/shape/shape_urdf.md): This file documents the MetriCal shape URDF command, which creates ROS-compatible URDF files from plex configurations for robotic system integration.

### configuration

- [Valid Data Formats](/metrical/configuration/data_formats.md): This file documents the supported data formats in MetriCal including MCAP files, ROS bags, folder datasets, and their respective message encodings and requirements.
- [Group Management](/metrical/configuration/groups.md): This file explains group management in the Tangram Vision Hub, including how to name groups, add members, assign roles, and manage organizational permissions for MetriCal usage.
- [Installation](/metrical/configuration/installation.md): This file provides installation instructions for MetriCal via apt repository for Ubuntu/Pop!_OS systems and via Docker for other operating systems.
- [License Creation](/metrical/configuration/license_creation.md): This file explains how to create personal and group licenses for MetriCal through the Tangram Vision Hub, including license naming, creation, and revocation procedures.
- [License Usage](/metrical/configuration/license_usage.md): This file provides comprehensive instructions for using MetriCal license keys, including command line arguments, environment variables, configuration files, and offline licensing options.
- [Visualization](/metrical/configuration/visualization.md): This file explains how to set up and use MetriCal's visualization features with Rerun for visual inspection of calibration data, detections, and spatial alignment verification.

### core_concepts

- [Components](/metrical/core_concepts/components.md): This file defines components as atomic sensing units in MetriCal's Plex system, detailing camera, LiDAR, and IMU component types with their intrinsic parameters and modeling approaches.
- [Constraints](/metrical/core_concepts/constraints.md): This file defines constraints as spatial, temporal, or semantic relations between components in MetriCal's Plex system, explaining directional conventions and extrinsic transformations.
- [Covariance](/metrical/core_concepts/covariance.md): This file explains covariance as a measure of uncertainty in MetriCal's Plex system, differentiating it from binary fixed/variable parameters and providing statistical modeling capabilities.
- [Object Space](/metrical/core_concepts/object_space_overview.md): This file explains MetriCal's Object Space concept, which refers to known sets of features in the environment used for cross-modality calibration and establishing metric scale.
- [Plex](/metrical/core_concepts/plex_overview.md): This file explains MetriCal's Plex concept, which represents the spatial, temporal, and semantic relationships within perception systems as a graph of components and constraints.
- [Projective Compensation](/metrical/core_concepts/projective_compensation.md): This file explains projective compensation, a phenomenon where errors in one calibration parameter affect other parameters due to correlation in observations or poor model choices.

### intro

This file introduces MetriCal, a tool for accurate and precise calibration of multimodal sensor suites with support for cameras, LiDAR, IMU sensors, and various calibration targets.

- [Welcome to MetriCal](/metrical/intro.md): This file introduces MetriCal, a tool for accurate and precise calibration of multimodal sensor suites with support for cameras, LiDAR, IMU sensors, and various calibration targets.

### results

- [MetriCal JSON Output](/metrical/results/output_file.md): This file documents MetriCal's comprehensive JSON output format containing optimized plex data, object space information, and detailed calibration metrics and residuals.
- [MetriCal Reports](/metrical/results/report.md): This file explains MetriCal's comprehensive calibration reports, including charts, diagnostics, metrics interpretation, and HTML report generation for calibration quality assessment.
- [Circle Misalignment](/metrical/results/residual_metrics/circle_misalignment.md): This file explains circle misalignment metrics unique to MetriCal, which measure the bridging between camera 2D features and LiDAR 3D point clouds using circular calibration targets.
- [Composed Relative Extrinsics](/metrical/results/residual_metrics/composed_relative_extrinsics.md): This file documents composed relative extrinsics error metrics in MetriCal, which measure consistency between relative extrinsics formed through object spaces and direct component transforms.
- [Image Reprojection](/metrical/results/residual_metrics/image_reprojection.md): This file explains image reprojection error metrics in MetriCal, which measure the precision of camera calibration by comparing feature positions in images to their object space counterparts.
- [IMU PreIntegration Error](/metrical/results/residual_metrics/imu_preintegration_error.md): This file documents IMU preintegration error metrics in MetriCal, which measure the consistency of IMU measurements across preintegration windows defined by navigation states.
- [Interior Points to Plane Error](/metrical/results/residual_metrics/interior_points_to_plane_error.md): This file explains interior points to plane error metrics in MetriCal, which measure the fit between LiDAR points detected on circular target surfaces and the actual target plane.
- [Object Inertial Extrinsics Error](/metrical/results/residual_metrics/object_inertial_extrinsic_error.md): This file explains object inertial extrinsics error metrics in MetriCal, which measure errors between sequences of measured and optimized extrinsics involving IMU navigation states.
- [Paired 3D Point Error](/metrical/results/residual_metrics/paired_3d_point_error.md): This file documents paired 3D point error metrics in MetriCal, which measure LiDAR alignment quality by comparing detected circle centers between different LiDAR frames of reference.
- [Paired Plane Normal Error](/metrical/results/residual_metrics/paired_plane_normal_error.md): This file documents paired plane normal error metrics in MetriCal, which measure LiDAR alignment quality by comparing detected plane normals of circle targets between LiDAR frames of reference.

### special_topics

- [Calibrate RealSense Sensors](/metrical/special_topics/calibrate_realsense.md): This file provides a tutorial for calibrating multiple Intel RealSense sensors simultaneously using MetriCal, including data recording procedures and calibration flashing.
- [Migrate from Kalibr to MetriCal](/metrical/special_topics/kalibr_to_metrical_migration.md): This file provides a comprehensive guide for migrating calibration workflows from Kalibr to MetriCal, highlighting operational differences and improved capabilities.
- [Experiment with Different Intrinsics Models](/metrical/special_topics/test_different_intrinsics.md): This file demonstrates how to quickly experiment with different camera intrinsics models using the same dataset in MetriCal, utilizing cached detections for faster iterations.

### support_and_admin

- [Billing](/metrical/support_and_admin/billing.md): This file explains how to create, cancel, and manage MetriCal subscriptions, payment methods, and billing contact information through the Tangram Vision Hub.
- [Contact Us](/metrical/support_and_admin/contact.md): This file provides contact information for MetriCal user support, partnering inquiries, and citation guidelines for academic research.
- [Legal Information](/metrical/support_and_admin/legal.md): This file contains legal disclaimers, confidentiality notices, and comprehensive third-party license information for the Tangram Vision Platform and MetriCal software.

### targets

- [Multiple Targets](/metrical/targets/multiple_targets.md): This file explains how to use multiple calibration targets simultaneously in MetriCal, including object space configuration, UUID generation, and target positioning for complex setups.
- [Target Construction Guide](/metrical/targets/target_construction.md): This file provides comprehensive guidance on constructing calibration targets for MetriCal, including target selection, printing considerations, and quality control measures.
- [Supported Targets](/metrical/targets/target_overview.md): This file documents all supported calibration targets in MetriCal including AprilGrid, markerboards, checkerboards, and LiDAR circle targets with their specifications and usage guidelines.