a9 doppler calibration

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EIVA Doppler log calibration

Date:05 March 2006 Version: 1.0 Page 1 of11

NaviPac-NT

NaviBat-NT

A9. Doppler Calibration


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Version History

Version Who Additions1.0 OKR 31 January 2000 Created


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Table of contents

1. INTRODUCTION....................................................................................................................................4

2. DL CALIBRATION....... ............. .................... .............. .................... .............. .................... .............. ......5

2.1 LOAD DATA SET......................................................................................................................................5

2.2 THE VIEW...............................................................................................................................................5

2.3 MANIPULATING DATA..............................................................................................................................7

2.4 CALIBRATION..........................................................................................................................................7

2.5 REPORT ..................................................................................................................................................8

3. DATA ............ .............. .................... .............. .................... .............. .................... ............. .................... ...11


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1. Introduction

The Doppler Calibration application allow the operator to load logged files, compare

raw position and Doppler track and calculate rotation and scale errors, which can be

applied to data to improve quality.

The application can be started from Start menu or by starting the application from the

browser:

The application can load NavBat data files (SBD format) or NaviPac survey data (XYZ

record format). Both file types must include:

raw position gyro

doppler log data


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2. DL Calibration

The program is based on the MDI technology, and it allows you to load multiple files

in the same application.

When started, you get the following empty look:

2.1 Load data set

To load a logged file, you must activate File, new or press the new icon.

A standard load from dialogue pops up:

Based on the file type (SBD for NaviBat and NPD for NaviPac), you may now load the

file.

If the load is OK, a new document is placed in the application display.

2.2 The view

The display contains one window per loaded file.


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The map view (as known in the NaviPac Helmsmans Display) contains two tracks:

The green line shows the raw stored track, i.e. not corrected for any offsets etc. The red line shows the doppler track, as its based on Doppler data, gyro and time.

The first position is based on first recorded position. The rest is just made by

adding vectors. X1 = X0 + delta-time * Speed-X.

As default the view shows the middle of the data set. Its now possible to

Re-centreDouble click anywhere in the view and the point will be defined as new centre. Zoom in

The default presentation is made in scale 1000, i.e. 1:1000. If you press the zoom-

in button, the scale is always reduced by a factor two, i.e 1000 -> 500 -> 250, etc.

Zoom out:The default presentation is made in scale 1000, i.e. 1:1000. If you press the zoom-

out button, the scale is always doubled.

Rotate the view:The default presentation is north up. If wanted, the presentation can be rotated in

steps of ten degree. This can either be done from menu (View, rotate right, View,

rotate left) or by pressing the rotate buttons.

If you have a nice data set, it can be printed by File, Print or by pressing the printer

button.

The map is now printed on any printer, and a small header is applied. Theheader

contains the following information:

Scale Centre position Number of points File name (do not use long path!) Current date/time


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The headers are formatted so it should fit to any printer driver, but we have observed

some minor cosmetic problems.

2.3 Manipulating data

If there is a clear difference between the raw track (green) and the Doppler track (the red),

the operator may perform a manual trial-and-error calibration by scaling and rotating the

Doppler track.

This can be done, by entering the following parameters by View, Scale and Rotate:

Scale Y:The along ship speed is increased or decreased by a multiplication factor

Scale X:The across ship speed is increased or decreased by a multiplication factor

Rotate:The direction (= gyro) of the vehicleis changed by adding the angle to the logged

direction.

When pressing OK, the graphical display is automatically updated by the entered

values.

The process can be repeated several times, as the corrections are combined:

Scale: Multiplied

Rotate: Added

By performing a stepwise refinement, the manually calibration can be performed until a

satisfactory fit is obtained between raw and Doppler Track.

The data report (See 2.5) will included the applied parameters.

We recommend that a graphical print always will be followed by an ASCII

print.

View, Reset Scale and Rotate can clear the corrections.

2.4 CalibrationWhen the Doppler data is used to improve raw Track in either Online or in NaviEdit, a

Rotation and Translation matrix equation can do this.


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This philosophy is used in the auto calibration (Edit, Calibrate or the Calibrate icon).

The data set is here merged using a Salomonsen Lite filter, which rotates and scales the

Doppler track until a best fit is obtained between the two tracks.

Normally the result is a smooth track, but here we pick-out the matrices instead and

use them as calibration results.

We can hereby get the following parameters, which is presented in the Calibration

report (See 2.5).

Scale Y:How much is the speed scaled in along ships direction

Scale X:How much is the speed scaled in across ships direction Rotate angle:

How much is the Doppler Track rotated.

Please note that it's very difficult to separate Scale-X and rotate angle.

If the data set is of high quality, the system will furthermore generate recommended

filter settings (for Online Salomonsen Lite Filter):

Maximum acceleration:The maximum observed acceleration. Higher values will be discarded in online.

Maximum position jumps:The maximum observed position jump. Higher values will be discarded in online.

Gain:Doppler weight - always 1.0000

The calculated values can be applied to the data by activating Edit, Apply correction.

We recommend that this command always is applied and that the result is

printed together with the report.

Please note that calibration is performed on manipulated data, i.e. any manually

corrections can have influence on the result.

2.5 Report

Information on the loaded data set, correction values and calculated corrections can be

obtained by the View, Report menu or by pressing the report icon.

The following dialogue then pops up:


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FileName of the loaded data file

Recorded:Data and time for the survey

File info Number of positions Number of Doppler records Manually entered rotation angle (See 2.3 Manipulating data) Manually entered scales

Calibration result Scale values Rotation angle Recommended online filter setting

If the operator presses Print, an ASCII file is generated on the same location as the data

file:EIVA Calibration report Date: 31-01-00 Time: 11:59:26---------------------------------------------------------------------File : S:\geofjord\J289N032.SBDRec. : 16.10.1999 19:13:16Report:File info:Positions 929 Doppler data 5425DL Rotated 0.000 degreeDL Scaled 1.000 in Y and 1.000 in X---------------------------------------------------------------------Calibrated:Scale Y: 0.980Scale X: 0.950Rotate A: 1.230Recommended filter setting (if data is typical sample withoutnoise):

Maximum acceleration: 1.884


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Maximum position jumps: 31.176Gain: 1.0000

The file is printed on the default Windows printer in pure ASCII.


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3. Data

The DL Calibration module operates on any data set, which is in the right format and

which contains both raw position and Doppler data.

What kind of data gives the best calibration result?

Its EIVAs experience that a good result is obtained if

1. The survey is performed as near as possible to straight lines2. Two or more individual data sets (in different direction) is calibrated and an

average result is taken

a9 doppler calibration

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