Change coordinate orientation!

We have a ADV with moveable sensor head - probe and sensor are connected by a cable.
Both are not orientated the same - heading, pitch and roll are different. I know that this can be corrected by the program ExploreV. But can you tell me how to use the displayed window 'Coordinate System'? Do I have to add or to subtract the different compoments?

Thanks!

Dear Hillie

The XYZ coordinate system of your probe is defined by the transformation matrix.  In a standard configuration, i.e unless a horizontal cansister is specified, the red probe (beam1) points in the x-direction and the z-axis points toward the transmit (center) transducer.  The y-axis follows the convention of a right-handed coordinate system.

If you collect data in XYZ, you can mount the probe in whatever direction you want.

If you want to collect data in ENU, you have to make sure the canister - which contains the compass and tilt sensors - is aligned with the probe. If it isn't, your velocity direction will be wrong.  Imagine that the probe is fixed mounted on the canister, and you will know how the cable probe should be oriented.

ExploreV cannot fix this afterwards.  If you have collected data with the wrong orientation and you want ENU data, you have to transform back to XYZ, change coordinates and the tranform back to ENU again.  A matlab script for doing this can be found here:

http://www.nortek-as.com/forum/software/644656788#696140964

Please let us know if you have any problems.

Best regards,

Atle Lohrmann

Hello,
Is the heading (the output given in the .sen vector file) the direction that Beam 1 (X-beam) is pointing toward?

- Yes, it is.  

Atle Lohrmann

but not for a cable probe?  The head doesn't have any way of recording direction except in XYZ does it?  Then the user records the X direction manually with a handheld compass?

Hi

The trick is to fix the cable probe orientation relative to the main canister - "as if" the probe had been fixed " />'>

- Atle

Hi,

1. How do I get the Vector absolute/resultant speed (v1, v2, v3) and direction from the ExploreVPro?

2. If Vector is mounted facing downward where the sensor is in the water and the pressure sensor is exposed in air, can it still records reading?

Please look at the attached data for reference. Thanks.

Urchinman

Hi there

Quote

1. How do I get the Vector absolute/resultant speed (v1, v2, v3) and direction from the ExploreVPro?

You don't.  Speed is a non-linear quantity so it is really not used much for scientific analyses. Sort of an engineering quantity - no offense.

Quote

2. If Vector is mounted facing downward where the sensor is in the water and the pressure sensor is exposed in air, can it still records reading?

Yes, the velocity measurements are independent of the pressure sensor reading.

Quote

Please look at the attached data for reference. Thanks.

I did take a brief look but it is hard to say much because the bursts are so short.  Was there a particular reason for why the bursts were so short?

- Atle Lohrmann

Hello Atle

I wonder if I collect data in ENU, but the probe is not aligned with the canister (there is an 30 deg angle between beam 1 and the horizontal canister), is there any way to fix the velocity. If I transform the back to XYZ, is it the "real" XYZ in the direction of probe?

Thanks

Best regards

Dehai Song

 

Previously hillie wrote:

Dear Hillie

The XYZ coordinate system of your probe is defined by the transformation matrix.  In a standard configuration, i.e unless a horizontal cansister is specified, the red probe (beam1) points in the x-direction and the z-axis points toward the transmit (center) transducer.  The y-axis follows the convention of a right-handed coordinate system.

If you collect data in XYZ, you can mount the probe in whatever direction you want.

If you want to collect data in ENU, you have to make sure the canister - which contains the compass and tilt sensors - is aligned with the probe. If it isn't, your velocity direction will be wrong.  Imagine that the probe is fixed mounted on the canister, and you will know how the cable probe should be oriented.

ExploreV cannot fix this afterwards.  If you have collected data with the wrong orientation and you want ENU data, you have to transform back to XYZ, change coordinates and the tranform back to ENU again.  A matlab script for doing this can be found here:

http://www.nortek-as.com/forum/software/644656788#696140964

Please let us know if you have any problems.

Best regards,

Atle Lohrmann

 

I'll assume you're working with a cabled probe Vector since that's the only way I can imagine there being a heading bias in the system. If you recorded in ENU coordinates the Vector doesn't know about any heading misalignment so you can transform back to XYZ and recover the instrument coordinate system. If you want to have unbiased ENU velocities you could then transform back to ENU with the heading corrected appropriately for the bias.

Thanks P.J. Yes, it's a cabled probe Vector. 

But how to correct the heading? Is it simply add or subtract the angle between beam 1 and canister to the recorded heading in .sen file?

Sorry I really know little about the heading.

Regards

Dehai

The compass is aligned with a small mark on the pressure canister. You'll need to measure the offset between this mark and beam 1 to adjust the heading. You mentioned a horizontal canister. The standard Vector setup has the compass mounted for the pressure canister to be vertical not horizontal. I'd check to make sure the heading, pitch and roll are reasonable values because of this. If the sensors weren't mounted at the factory for horizontal deployment at least the pitch or roll should be near 30 degrees. You can also check the status and error codes in the *.sen file. If these indicate errors, you can still recover XYZ velocities, but won't be able to obtain valid ENU velocities.

I am trying to process some Vector data (non-cable) collected 4 years ago (!). I didn't do the deployment myself, but I can see in the .hdr file that the coordinate system is XYZ and I have also heading, pitch and roll recorded  in the .sen file. I would like to convert my velocities to ENU system and I have read all the related postings in this forum, but I am still a little bit confused. 

Is there a matlab script (or any other software) where I can input XYZ velocities and angles and get the ENU velocities? 

Thank you very much in advance

The cabled Vector I used shows "Vector horizontal tilt" outside the canister. So I believe the compass is mounted for the canister to be horizontal.

The vector was deployed as the drawing in N2008-137 with probe upwards, except the mismatch between beam 1 and the direction of canister.

However, the status codes in the *.sen file shows both pitch and roll are out of range. What's the problem?

I also uploaded the *.sen file. Could you please help me check it?

Thank you.

Regards

Dehai

 

Previously P.J. Rusello wrote:

The compass is aligned with a small mark on the pressure canister. You'll need to measure the offset between this mark and beam 1 to adjust the heading. You mentioned a horizontal canister. The standard Vector setup has the compass mounted for the pressure canister to be vertical not horizontal. I'd check to make sure the heading, pitch and roll are reasonable values because of this. If the sensors weren't mounted at the factory for horizontal deployment at least the pitch or roll should be near 30 degrees. You can also check the status and error codes in the *.sen file. If these indicate errors, you can still recover XYZ velocities, but won't be able to obtain valid ENU velocities.

 

Hmmmm, it seems like the attitude sensors are not actually mounted for horizontal deployments or the instrument might have been reassembled incorrectly. To verify how the sensors are mounted, try moving the pressure canister between a vertical and horizontal orientation while recording data. Try to find an orientation with near zero pitch and roll. This will tell you how the sensors are installed and which way the pressure canister needs to be mounted.

Unfortunately, the data you have currently can't be transformed into ENU coordinates without valid pitch and roll. You can still recover the XYZ data and analyze it.

P.J.