Intel RealSense D400 Series User manual

Intel®RealSense™ Depth Module
D400 Series Custom Calibration
Revision 1.1.0
January 2018

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Contents
1Introduction ....................................................................................................... 8
1.1 Purpose and Scope of This Document ........................................................ 8
1.2 Organization .......................................................................................... 8
2Overview .......................................................................................................... 9
2.1 Calibration API and Calibration Data Read/Write/Restore ............................. 9
2.2 Calibration Parameters .......................................................................... 10
2.3Frame Formats Used in Custom Calibration .............................................. 11
2.4 Frame Sync.......................................................................................... 11
2.5 Accuracy.............................................................................................. 11
3Setup ............................................................................................................. 13
3.1 Hardware............................................................................................. 13
3.1.1 Device.................................................................................... 14
3.1.2 Target .................................................................................... 14
3.1.3 Tripod .................................................................................... 15
3.1.4 USB ....................................................................................... 17
3.1.5 PC ......................................................................................... 17
3.2 Software.............................................................................................. 17
3.2.1 Custom Calibration Sample Application....................................... 17
3.2.2 Intel® RealSense™ Calibration Tool and API ............................... 18
3.2.3 Intel® RealSense™ SDK........................................................... 19
3.2.4 OpenCV 3.3.0 ......................................................................... 19
3.2.5 Glut Library ............................................................................ 20
4Calibrating Device with Custom Calibration Sample Application.............................. 21
4.1 Process Overview.................................................................................. 21
4.2 Connect Device to Computer .................................................................. 21
4.3 Running Custom Calibration Sample Application ....................................... 21
4.3.1 Starting Application ................................................................. 21
4.3.2 Capturing Images from 6 Viewpoints.......................................... 22
4.4 Calibration Result.................................................................................. 35
4.5 Updating Results to Device..................................................................... 37
4.5.1 Depth Quality Check before Updating Calibration ......................... 38
4.5.2 Writing Optimized Calibration to Device ...................................... 38
4.5.3 Depth Quality Check after Updating Calibration ........................... 40
5Developing Custom Calibration Application.......................................................... 42
5.1 Sample Application Source Code and Compile........................................... 42
5.2 Calibration Mode Camera Configuration ................................................... 44
5.2.1 Emitter................................................................................... 44
5.2.2 Auto Exposure......................................................................... 44
5.2.3 Streaming Resolution and Format .............................................. 45
5.2.4 Image Captures....................................................................... 45
5.2.5 Demosaic Left/Right Images for ASR / PSR SKUs ......................... 45
5.3 Detecting the Chessboard in an Image with OpenCV ................................. 45

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5.4 Calculating Depth Camera Calibration with OpenCV................................... 46
5.5 Calculating RGB Camera Calibration with OpenCV ..................................... 47
5.6 Calculating RGB Camera Calibration Extrinsics with OpenCV....................... 47
5.7 Writing Calibration Parameters ............................................................... 48

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Tables
Table 2-1. Frame Formats Used in Custom Calibration.......................................... 11
Table 3-1. Intel® RealSense™ Calibration API Resources ..................................... 18
Table 3-2. Intel® RealSense™ SDK Resources .................................................... 19
Table 3-3. OpenCV 3.3.0 Resources ................................................................... 20
Table 3-4. OpenCV 3.3.0 Libraries Required for the Example................................. 20

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List of Figures
Figure 2-1 Software Stack with Dynamic Calibration API and Calibration Apps........... 9
Figure 3-1 Hardware Setup ............................................................................... 13
Figure 3-2 D415 Device .................................................................................... 14
Figure 3-3 8x7 60x60 mm Checker Calibration Target .......................................... 15
Figure 3-4 Tripod............................................................................................. 16
Figure 4-1 Center Right Position ........................................................................ 25
Figure 4-2 Viewpoint #1 ................................................................................... 26
Figure 4-3 Center Right .................................................................................... 27
Figure 4-4 Viewpoint #2 ................................................................................... 28
Figure 4-5 Left ................................................................................................ 29
Figure 4-6 Viewpoint #3 ................................................................................... 29
Figure 4-7 Right .............................................................................................. 30
Figure 4-8 Viewpoint #4 ................................................................................... 31
Figure 4-9 Top Looking Down............................................................................ 32
Figure 4-10 Viewpoint #5 ................................................................................. 33
Figure 4-11 Bottom Looking Up ......................................................................... 34
Figure 4-12 Viewpoint #6 ................................................................................. 34
Figure 4-13 Depth Quality before Updating Calibration ......................................... 38
Figure 4-14 Updating Calibration Parameters to Device ........................................ 39
Figure 4-15 Calibration Parameter Change .......................................................... 40
Figure 5-1 General Process for custom Calibration ............................................... 42

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Revision History
Document
Number
Revision
Number
Description
Revision Date
XXXXXX
1.0
Initial Release
01/2018
1.1
Update with Calibration API 2.5.2.0 release
01/2018

Introduction
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1Introduction
1.1 Purpose and Scope of This Document
In order to operate Intel® RealSense™ D400 device efficiently and accurately, users need
to make sure the device is well calibrated. The Intel supplied calibration tools including
Intel® RealSense™ Dynamic Calibrator and OEM Calibration Tool for Intel® RealSense™
Technology are designed to calibrate the devices using Intel proprietary algorithms.
Some customers or developers may choose to use their own calibration algorithms and
update the device with their custom calibration data.
This document contains technical information to assist those developing custom
calibration solutions for Intel® RealSense™ D400 series modules. The primary goal is to
guide the user how to create a calibration application, using the D400 corresponding
APIs. This includes a description how to configure the device under calibration, define
the calibration parameters, and how to read/write these parameters from/into the
device. In addition, a simple sample application based on OpenCV algorithm is
provided as an example.
It is not in the scope of this document to discuss details of calibration algorithm or
accuracy. Developing custom calibration requires knowledge in computer vision as well
as good understanding of the RealSense device operating details. It is a complex topic
and intended only for those with expert level knowledge.
1.2 Organization
This document is organized into four main parts: overview, setup, calibrating a device
with custom calibration sample app, and developing custom solution:
Overview –brief overview of the Calibration API and parameters.
Setup –hardware and software setup for running the Custom Calibration
Sample App to calibrate a device and developing custom calibration solutions.
Calibrating Device with Custom Calibration Sample App –describes the
necessary hardware and software setup required running the Custom
Calibration Sample App and details steps to calibrate device.
Developing Custom Calibration Solution –uses the sample application as an
example to describe details of steps implementing a custom calibration
solution for Intel® RealSense™ D400 series modules.

Overview
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2Overview
2.1 Calibration API and Calibration Data
Read/Write/Restore
Intel provides a software interface in Calibration API to enable user uploading those
calibration parameters to Intel® RealSense™ D400 devices and read the parameter
back from device:
WriteCustomCalibrationParameters –write parameters to device
ReadCalibrationParameters –read parameters from device
Figure 2-1 Software Stack with Dynamic Calibration API and Calibration Apps
An example tool CustomRW is also included in Calibration API to read calibration
parameters from XML file and write them to the device.
A user custom calibration app can choose one of the two approaches to update the
results to the device:
To link to the WriteCustomCalibrationParameters and
ReadCalibrationParameters and write directly to the device through the APIs.

Overview
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To write the results into a parameter XML file and then use CustomRW to
read/write the parameters to the device.
In case user needs to restore the calibration data on the device,
ResetDeviceCalibration in Calibration API can be called to programmatically restore
the device calibration to gold settings.
ResetDeviceCalibration –restore device calibration to gold settings
The CustomRW example tool also supports restore through command line option.
2.2 Calibration Parameters
Calibration parameters includes INTRINSICS and EXTRINSICS. Assume left camera is
the reference camera and is located at world origin. RGB parameters only apply to
modules with RGB, e.g., D415 and D435.
Intrinsic includes
Focal length - specified as [fx; fy] in pixels for left, right, and RGB cameras
Principal point - specified as [px; py] in pixels for left, right, and RGB cameras
Distortion - specified as Brown's distortion model [k1; k2; p1; p2; k3] for left,
right, and RGB cameras
Extrinsic includes
RotationLeftRight - rotation from right camera coordinate system to left camera
coordinate system, specified as a 3x3 rotation matrix
TranslationLeftRight - translation from right camera coordinate system to left
camera coordinate system, specified as a 3x1 vector in millimeters
RotationLeftRGB - rotation from RGB camera coordinate system to left camera
coordinate system, specified as a 3x3 rotation matrix
TranslationLeftRGB - translation from RGB camera coordinate system to left
camera coordinate system, specified as a 3x1 vector in millimeters
The calibration data read/write API allows user to upload both INTRINSICS and
EXTRINSICS. The user custom algorithm is free to optimize all these parameters. The
sample in this document optimizes both intrinsic and extrinsic parameters.
The following table shows how the various calibration tools would impact calibration
parameters for Intel® RealSense™ D400 series depth cameras.
Factory
Calibration
OEM
Calibration
Technician
Calibration
User Custom
Calibration
Dynamic
Calibration