Vessel and Sensor Coordinate System Schema

Originated by Shawn Smith (FSU) on October 11, 2011

 

From: Shawn R. Smith (FSU) on Tue, 11 Oct 2011

Hello all,

 

As part of the Rolling Deck to Repository project, I coordinated an effort to draft a specification to define a coordinate system schema that could be used by operators to provide x, y, z locations of sensors and devices on their vessels. Several of your colleagues contributed to the development of the draft and we continue to receive input on the specification.

 

I would now like to make you all aware that the draft schema is available on the R2R web site at: http://www.rvdata.us/operators/coordsys

 

I welcome additional comments on the schema. We tried to make the specification as flexible as possible to meet the needs of numerous vessel types and operational mission requirements.

 

If you are interested, please review the document and submit your comments to me by 4 November 2011. I will compile the comments prior to RVTEC 2011 and will have them available for discussion in New Orleans.

 

Best regards,

 

Shawn

------------------------------------------------------------

Mr. Shawn R. Smith

Research Meteorologist

Director, R/V Data and FSU Winds Center

 

Center for Ocean-Atmospheric Prediction Studies (COAPS)

Florida State University

 

 

Reply From: Dale Chayes (LDEO) on Tue, 11 Oct 2011

 

This is a good step.

 

Because this protocol is likely to (should?) result in long-life metadata (well beyond the "real-time" transfer from ship to shore), I think this needs to state that for the (any, each, all) origin(s):

 

+  X==0, Y==0, Z==0  has to be at a physical location on the vessel, and

 

+  your schema ought to provide for a link to a URI where one can find more info, e.g. a descriptive document, the survey docs, links to other coordinate systems, etc.

 

With regard to the origin of the coordinate system, I believe that it should be at a well marked,  physical location because:

 

+ to be useful it has to survive for the lifetime of the vessel (as sensors, surveys, and users come and go), and

 

+ it would be very complex (== expensive) if not problematic to accurately re-survey to add new sensors if there is no physical "mark" to re-occupy (in the surveyor's terminology.)  Lacking a physical mark (or marks) to work from a new survey to add new sensors would have to establish a new origin by surveying all of the known sensors and working backward.

 

None of this imposes any limits on the needs of a particular user who might want some particular set of data referenced to some other (perhaps transient, such as metacenter or center of motion) location for a particular experiment or analysis.

 

Thanks for moving this forward,

-Dale

 

 

Reply from: Webb Pinner (URI) on Tue, 11 Oct 2011

 

Dale beat me to it.

 

One additional comment: Is it worth being able to differentiate between versions of a vessel's origins should the origin move during the life of the vessel (i.e. because of a major mid-life conversion similar to lengthening of the Knorr and the Endeavor)?

 

- Webb

 

 

Reply from: Brent Evers on Tue, 11 Oct 2011

 

Dale and Webb both make good points on a physical location being marked.  I'll add that making sure that that location accessible and also easily measured from is important in adding future instruments and systems.

 

A number of years ago I was involved in a cruise on the Palmer in which a drill rig was errected on the aft deck.  To maintain position over the drill pipe, the vessel needed to have the dynamic positioning system referenced to the moon pool (where the drill pipe passed through).  To do so required accurate survey of the GPS antenna array on the mast, and the INS buried down near the multibeam.  A "reference point" had been previously arbitrarily (probably a guess at CB) established (and all data on the vessel taken subsequently - for at least ten years) at frame number X and Y feet above the keel, which to the best of my recollection ended up about three feet in the air above the main deck and somewhere in the bath room wall.  Measuring from known bulkheads (related to know frames and from walls - assuming the drawings we had were actually as builts) probably put us within a foot or so of the hypothetical spot.  The point is - it doesn't really matter where it is (any position can be related to any other position), but make sure its in a place where you can put a tape measure on it.  One foot of error turns into an error radius, which gets big and adds up quick when you try to do things you don't anticipate (like drive a boat) from it.

 

Brent