Image Engineering GEOCAL Manuale utente

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GEOCAL

User Manual

1. December 2020

Image Engineering

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Content

1INTRODUCTION............................................................................................................. 3

Intended use............................................................................................................. 3

General safety information........................................................................................ 3

2GETTING STARTED....................................................................................................... 4

Scope of delivery ...................................................................................................... 4

Commissioning ......................................................................................................... 4

3OPERATING INSTRUCTIONS HARDWARE.................................................................. 5

GEOCAL................................................................................................................... 5

Diffractive Optical Element (DOE)............................................................................. 5

Camera settings........................................................................................................ 5

3.3.1 Camera position and suitable lenses.................................................................. 6

3.3.2 Exposure............................................................................................................ 7

4OPERATING INSTRUCTIONS SOFTWARE .................................................................. 8

Installing GEOCAL software...................................................................................... 8

Configuration File (XML) ........................................................................................... 8

Loading images for analysis.....................................................................................10

Image analysis.........................................................................................................10

Saving results ..........................................................................................................12

Logging....................................................................................................................12

Quit..........................................................................................................................12

TRADEMARK AND COPYRIGHT............................................................................12

5ADDITIONAL INFORMATION .......................................................................................13

Disposal instructions................................................................................................13

6DATA SHEET ................................................................................................................14

Overview..................................................................................................................14

Features...................................................................................................................14

6.2.1 [Hardware] Integrating sphere, Mount...............................................................14

6.2.2 Illumination........................................................................................................14

6.2.3 Software............................................................................................................14

General description hardware ..................................................................................15

Requirements on the device under test (DUT) .........................................................15

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1 INTRODUCTION

Important information: Read the manual carefully before using the device.

Inappropriate utilization may cause damage to the device.

Intended use

GEOCAL consists of an illuminating hardware device and software for geometric calibration of camera

systems. The GEOCAL software is used for calculating the calibration parameters from a single image

taken with a camera system of the point grid generated by the GEOCAL hardware device.

•Only suitable for indoor use.

•Place the system in a dry and constant tempered environment. Avoid high air humidity.

General safety information

WARNING! GEOCAL uses a laser diode for illumination.

LASER RADIATION CLASS 1M LASER PRODUCT

•Do not stare into beam

•Do not view directly with optical instruments

•Do not open the housing of GEOCAL under any circumstances

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2 GETTING STARTED

Scope of delivery

•GEOCAL hardware device

•Latest software version on USB storage device

•Power supply + cable

•USB cable (type B to type A)

•Test report

Commissioning

•Remove the packaging material.

•The power socket is located on the left-hand side of the device next to the USB type B socket.

The main power switch is located on the right-hand side. Connect GEOCAL to a power outlet

and switch it on.

Please note: the blue LED next to the power switch indicates that the power line is active and

GEOCAL is ready for operation.

•Install the latest GEOCAL software (Windows, 64bit)

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3 OPERATING INSTRUCTIONS HARDWARE

GEOCAL

After switching on, GEOCAL is ready for use. No warm-up phase is required.

Diffractive Optical Element (DOE)

A diffractive optical element (DOE) is used to split the incoming beam of light and generate a calibration

grid of evenly distributed light spots with a wavelength of 633 nm. The DOE is mounted on the front of the

GEOCAL device (visible glass plate mounted in circular cutout, see Figure 2).

Camera settings

Set the camera to manual exposure mode. If manual mode is not available, use the automatic exposure

mode. For best results, the image should be saved in a lossless image format. TIFF format is

recommended, PNG and JPEG (lossy) are also supported. If you convert RAW image data to another

format, make sure the image is being debayered in the process.

Auto focus must be turned off. Since GEOCAL uses a collimated light beam virtually originating from

infinity, the appropriate focus distance will be near infinity. Using manual focus, make sure that the

camera is focused on the light points.

Exposure program

Manual

Aperture

No default value

ISO Speed

Lowest value (e.g.,100)

Auto focus

Off

File type

TIFF recommended, PNG

and JPEG also supported

DOE

Figure 1: Calibration grid

(the brightest spot marks the center)

Figure 2: Location of the DOE

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3.3.1 Camera position and suitable lenses

Place the camera in front of the diffractive optical element that is located in the circular opening on the

front of GEOCAL.

The camera can be placed directly in front of the DOE, no minimum distance is needed (view Figure 3

below). The principal axis of the lens should be aligned approx. perpendicular to the DOE. Do this by

aligning the 0th diffraction order, which is the brightest spot in the center of the grid, with the center of the

image. See Figure 4 for reference. Make sure that the point grid covers the whole image and that the

border of the DOE is not visible.

The top side of Geocal and the top side of the camera must have the same orientation. A rotation of the

camera around the optical axis of approx. +/- 2° will be tolerable.

No further alignment steps are necessary. The mapping of the light points is not influenced by the

translation of the camera. The rotation of the camera to the DOE is part of the calibration and is

determined during the process and reported as part of the result.

The front element of the lens must not be larger than 77 mm in diameter in order to capture the point grid

in full format. GEOCAL has been tested using various lenses with a field of view between 30° and 120°.

Avoid using lenses that exceed or fall below these values, otherwise, no reliable calibration results can be

guaranteed.

Figure 3: Setting the distance between camera and GEOCAL

Figure 4: Good alignment (0th order in center of image) Bad alignment (0th order far off center)

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Note: Please use caution when positioning the camera. The DOE is made of glass and has a

thickness of only 1.5 mm.

Ensure that the calibration is performed in a dark environment to avoid stray light, reflections, or

similar interfering factors.

3.3.2 Exposure

For best results, the exposure should be selected so that the individual light points are not saturated (i.e.,

no white pixels or a minimal amount of white pixels in the center of each point) with excepton of the 0th

diffraction order. The 0th order will always be much brighter than the points surrounding it. See Figure 5

below for an example.

Depending on your camera you might encounter different problems:

The exposure time of my camera cannot be set short enough to avoid saturation.

Possible solutions:

- Set the ISO to the lowest native value available (ISO 100 for most cameras)

- Stop down the aperture if possible

- If the image is still too bright, you could use an ND-Filter to reduce the amount of light

reaching the image sensor

The intensity dropoff is too steep towards the edges of the image. There are no more points

visible.

This problem may occur for ultra wide-angle lenses. If the images can not be properly analyzed, try the

following.

Generate an HDR image by taking multiple images of the point grid using a range of exposure times (do

not change aperture settings in this case) and combine them to a high dynamic range image in order to

achieve more or less uniform exposure across the entire sensor. Do not change the orientation of the

camera in between images because the points would be no longer aligned to one another through

multiple images.

Figure 5: Suitable exposure (dark backgroumd, small points) Exposure too bright (red background, larger, saturated points)

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4 OPERATING INSTRUCTIONS SOFTWARE

The GEOCAL software enables you to perform a complete calibration of your camera system in a matter

of seconds.

The results can be saved as CSV or XML files.

Installing GEOCAL software

•Execute the GEOCAL installer (GEOCAL_Vx.x.x.exe, 64 bit) and follow the instructions.

•The software is now ready for use.

Configuration File (XML)

A standard config file will be installed with the software. If your calibration does not require very specific

settings you do not need to load a config file or manipulate the existing one.

If you do need to make adjustments, the parameters of the config file are listed below.

•Control Parameter: MinF

This parameter describes the stop strategy, at which optimization value the analysis is stopped

(0.0…10.0 – default: 1.0)

The smaller the value, the more accurate the analysis becomes, but the analysis time also

increases.

•Control Parameter: MinDelta

This parameter describes another stop strategy. When the change of the optimization value

between two iterations is less than the delta, the analysis stops (0.0...10.0 - default: 1e-7).

The smaller the value, the more accurate the analysis becomes, but the analysis time also

increases.

•Analysis Parameter: angles Alpha and Beta

These angles describe the orientation of the diffractive optical element to the incident expanded

and collimated beam of light. They are determined during the acceptance procedure at Image

Engineering and written in the config file. These values may not be changed unless the diffractive

optical element has to be replaced.

Nevertheless, they can, for example, be set to zero for troubleshooting.

•Analysis Parameter: angles Omega (roll), Phi (pitch), Kappa (yaw)

These angles describe the orientation of the device under test to the diffractive optical element.

These values are determined during calibration and output as results. Nevertheless, they can be

set to a fixed value for troubleshooting.

•Analysis Parameter: Radial Distortion Coefficients 1-5

The radial distortion coefficients model this type of distortion. The distorted points are denoted as:

xdistorted = x(1 + k1*r2+ k2*r4+ k3*r6+ k4*r8+ k5*r10)

ydistorted= y(1 + k1*r2+ k2*r4+ k3*r6+ k4*r8+ k5*r10)

These values are determined during calibration and output as results. However, they can be set

to a fixed value for troubleshooting.

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•Analysis Parameter: Tangential Distortion Coefficients 1+2

The tangential distortion coefficients model this type of distortion. The distorted points are

denoted as:

xdistorted = x + [2p1xy + p2(r² + 2x²)]

ydistorted = y + [p1(r² + 2y²) + 2p2xy]

These values are determined during calibration and output as results. However, they can be set

to a fixed value for troubleshooting.

•Analysis Parameter: Focal Length Xand Y

The focal length values of the device under test in X and Y are determined during calibration and

output as results in pixel dimensions. Nevertheless, they can be set to a fixed value for

troubleshooting.

•Analysis Parameter: Skew coefficient

The skew coefficient is set to 0 by default. It is non-zero if the image axes are not perpendicular.

•Analysis Parameter: Principal Point

The principal point (optical center) describes the point where the optical axis of the camera lens

intersects the image sensor. It is determined during calibration and output as a result.

Nevertheless, it can be set to a fixed value for troubleshooting.

To make changes to the standard config file, open it in a text editor. It is advised to make a copy of the

standard version before editing it.

Editing Control Parameters:

Example:

The “Use” flag indicates if the following value is used for the calibration procedure. If it says “false”, it is

not used and the standard value is used instead. To use a custom value, write “true” instead of “false”

and change the value (“0.1”in this example) as desired. The new value will be used in every calibration

until you set the “Use” flag back to “false” again.

Editing Analysis Parameters:

Example:

The “SetToInvariant” flag indicates if the following value is calculated during calibration or set to a fixed

value. If it is set to “false”, the value is calculated in each calibration. To set it to a fixed value, write “true”

instead of “false” and change the value (“0” in this example) as desired. The new value will be used in

every calibration until you set the “SetToInvariant” flag back to “false” again.

Loading a config file:

Click File →Load configuration (ctrl+c) →navigate to the folder containing the file →select the file and

click “open”.

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Loading images for analysis

Click File →Load images (ctrl+o) →navigate to the folder containing the images →select one or multiple

images and click “open”.

In the current state, the software supports the analysis of 8bit and 16bit images.

The following file types are supported (debayered images): .TIFF, .JPG, .PNG

Images for analysis need to be taken so that the point grid fills the sensor completely.

Image analysis

•Image selection: Select an image from the list in the “Image data” section (1). The image will

then be visualized in the “Image” section (4) under the “Image” tab. You can zoom into and out of

the image using your mouse wheel. The zoom will be centered around the position of your cursor.

•Point detection: Detect the points in the image by pressing the “Detect” button in the “Detection

& analysis” (2) section.

Detection is finished when the progress bar at the bottom of the window (5) reaches 100%. By

pressing “Show Detected Grid” next to the progress bar, you can display a visualization of the

detected/undetected points.

Figure 6: Software user interface overview

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