memo - processing north up usbl data in vbaproc

MEMO REPROCESSING NORTHUP USBL DATA IN VBAPROC

Memo - Processing North Up USBL data in VBAProc.doc Page i

0 Initial version J. Callahan J. Callahan J. Callahan 08/02/2011 Rev Description Prepared Checked Approved Date

MEMO

REPROCESSING NORTHUP USBL DATA IN VBAPROC


Memo - Processing North Up USBL data in VBAProc.doc Page ii

CONTENTS Page

1. INTRODUCTION 1

2. VBAPROC PROJECT PREPARATION 1 2.1 Replace NEL Groups 1 2.2 Add NEL Groups 2

3. PROCESSING SCRIPTS TO RECALCULATE NORTH UP USBL DATA 3 3.1 Standard Sensor Processing 4 3.2 Special Processing Scripts 4

3.2.1 Proc-General Purpose 4 3.2.2 RecalcUSBLOffset 6


Memo - Processing North Up USBL data in VBAProc.doc Page 1

1. INTRODUCTION

USBL systems output a variety of formats and modes. Commonly a USBL system is set-up to output in Vessel Up relative coordinate mode. If at all possible this is the recommended output mode.

However, on vessels were Fugro is not allowed to effect changes to the USBL system it is sometimes that we have to handle North Up relative coordinates. In this case, our software (Starfix.USBL) is able to utilize the data in either North Up or Vessel Up coordinate frames. However, in post-processing, without special processing scripts we can only work with Vessel Up relative coordinates. This can be overcome by installing special processing scripts included in a Release Candidate.

Reprocessing of North reference data in VBAProc requires the following minimum software.

Starfix Suite 9.1 Starfix Suite 9.1 RecalcUsblOffset RC2

Once installed the user must following the steps as outlined in the Advice Notes document included with the RC. This document will detail the process of preparing a VBAProc project for using these scripts and the steps required to recompute the North Up USBL data to a beacon position.

2. VBAPROC PROJECT PREPARATION

Preparing the VBAProc project requires removing several default NEL groups and adding back a new version supplied in RecalcUsblOffset RC2.

2.1 Replace NEL Groups

Any new or existing VBAProc project will contain several NEL groups required to process USBL data. Of these groups several need to be replaced with a version supplied in RecalcUsblOffset RC2. First the old NEL groups need to be removed. The following NEL groups need to be replaced:

RecalcUSBLOffset UsblDevice UsblProc

Removal is done using the 'Remove NEL group function from the Edit menu:



Select each of the groups and press the 'Remove NEL group' button

2.2 Add NEL Groups

After the removal of the NEL groups add the new version using the function in the Edit menu



The release candidate will have placed new versions of these groups in the default NEL template folder of the Starfix Suite installation as shown below.

3. PROCESSING SCRIPTS TO RECALCULATE NORTH UP USBL DATA

Processing data to recompute a USBL position requires several standard processing scripts and those special for North Up relative USBL data provided in the release candidate.



3.1 Standard Sensor Processing

Processing of North Up USBL data to create a beacon position requires standard processing of all sensors ancillary to the USBL system:

Position (USBL reference position) Heading (USBL heading device and optional survey gyro to use) PitchRoll (Only if the USBL data is not already PitchRoll corrected [Note: USBL data not already PitchRoll corrected is rare])

3.2 Special Processing Scripts

Two Visual Basic scripts are included in the release candidate to process the North Up USBL data

Proc-GeneralPurpose RecalcUsblOffset

3.2.1 Proc-General Purpose

Proc-GeneralPurpose was modified to process North Up USBL data. This script takes the North UP data and a Heading file and converts to Vessel Up relative coordinates. The Heading file used should be the same as originally used to create the North Up data, therefore the USBL systems Heading.



To determine if the UBSL data is North Up or Vessel Up the script uses the Mode field of the USBL beacon in the USBLBeaconDevice NEL group.

USBL Mode is based on several factors

Value Mode Description 1 Cartesian X, Y, Z Co-Ordinates Type Data 2 Polar Range, Bearing, Depth Type Data = 2 4 North Up Beacon Data Is Relative To True North 8 Vesse Up Beacon Data Is Relative To The Vessel Up 16 Towed Beacon Is Towed (Setting In Usbl Module) =

16 32 Free Swimming Beacon Is Free Swimming (Setting In Usbl

Module) 64 Motion

Corrected Motion Has Been applied (Setting in Usbl module)

37 = Free Swimming (32) + North Up (4) + Cartesian (1)

The UsblDevice NEL group was altered to support reprocessing the USBL for refraction correction. To correct for refraction the script needs to know where the USBL transducer is (OffsetName) and where the data that is being processed is relative from (UsblReferenceOffset). Refraction correction is not done during the initial processing of the data (Proc-GeneralPurpose), but at the time the position is being calculated (RecalcUsblOffset).

The actual processing done in Proc-GeneralPurpose is:

Convert North Up to Vessel Up (Mode [NEL USBLBeaconDevice] has North Up flag set = 4) Correct for Pitch, Roll, Heading & Scale Factor [NEL UsblDevice]



The UsblProc NEL group was altered to support use of North Up USBL data. The change was to add a reference to a Heading device to convert the North Up data to Vessel Up relative (HeadingDevice).

Heading device used to convert North Up to Vessel Up relative should be the same that was used to create the North Up data. This would be the same Heading device used by the Usbl system.

3.2.2 RecalcUSBLOffset

To recalculate the beacon position using the new NEL groups use the script supplied in the release candidate (VBA script in the USBL node).



The RecalcUsblOffset NEL group was altered to support reprocessing the USBL for refraction correction. To reprocess using refraction correction the field UseRefraction must be enabled. If enabled then the script will use the offsets described in the UsblDevice for the sensors location (OffsetName) and where the data in the file is relative from (UsblReferenceOffset). Using this option also requires a Cast library to determine the sound velocity profile to use.

On successfully running of the script a new beacon position file is created:

--Position.pos

memo - processing north up usbl data in vbaproc

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