Coordinate systems: NEU, ENU, NEU and NED

Thanks to Carl for posting the message and OGC spec to this list.  
> Date: April 23, 2010 9:42:56 AM EDT
> To: <public-geolocation@w3.org>
> Subject: RE: Geolocation - OGC GML profile for "Moving Snapshot"


In watching progress in this list in comparison to other lists, an item of common interest are definitions of the coordinate systems:  NEU, ENU, NEU and NED  

Below are comments on coordinate systems in the two of the W3C draft geolocation draft specs with comparison to the OGC spec.


*** Geolocation API Specification
Editor's Draft 10 February 2010
http://dev.w3.org/geo/api/spec-source.html
5.4 Coordinates interface
"The heading attribute denotes the direction of travel of the hosting device and is specified in degrees, where 0° ≤ heading < 360°, counting clockwise relative to the true north."


*** Orientation Event Specification
Editor's Draft 05 March 2010
http://dev.w3.org/geo/api/spec-source-orientation.html
4.1 Device orientation
"The orientation of the device is given in terms of the transfromation from a coordinate frame fixed on the Earth to a coordinate frame fixed in the device."
"The Earth coordinate frame is a 'Noth, East, Up' frame at the user's location."

Two reasons to reconsider North-East-Up in the Orientation Event Spec:
- North East Up is a "left handed" coordinate reference system.  Sometimes ENU is used as it is a right hand system, but then orientation is counterclockwise.
- Choosing NEU in Orientation may be confusing with respect to the implied NED choice made in the Geolocation API spec


*** The OGC moving snapshot spec made these choices:
5.3  Local Tangent plane 
"The velocity in MovingObjectSnapshot is defined relative to Euclidean plane corresponding to a Local Tangent Plane (LTP) at the location of the object.  The LTP is defined with its origin at the point where the object is located on (or possibly near) the Earth’s surface. LTP is oriented in three dimensions with the vertical axis taken to be straight down, parallel to the gravitational gradient, with the plumb line. The other two axes are perpendicular to the vertical axis aligned with local geographic north and east."

7  Schema for MovingObjectSnapshot'
Heading "...value must be in degrees measured clockwise from due North"

That is the OGC spec uses N-E-D.  This helped us resolve issues similar to those in comparing the geolocation and orientation spec.


*** Martin Thomson's message to the list on April 21st discussed how to define Down.  That message included an attachment: WhatsUp.pdf.
Its not clear from that message on the 21st what choice was made regarding the alignment of the up axis.
The draft OGC spec puts "the vertical axis taken to be straight down, parallel to the gravitational gradient, with the plumb line." 



Regards,
George





On Apr 23, 2010, at 9:42 AM, Carl Reed wrote:

> Dear W3C Geolocation  community -
>  
> George Percivall of the OGC asked that we share the attached document with this group: OGC MovingObjectSnapshot: An application schema of the OGC Geography Markup Language. From the scope of the Moving Snapshot document:
>  
> This document defines a GML application schema to encode a snapshot of a moving object including its location, translational velocity and acceleration. This specification addresses the use case of a solid object, such as a car, travelling in a plane local to the object, such as a street.  The velocity is an instantaneous vector composed of a scalar speed and a heading relative to North.
>  
> Due to the dozens of use cases that OGC Members have identified for describing a moving object, we hope that you find this specification useful. We would also ask that if you have any comments, suggestions, or questions, please let us know.
>  
> Finally, this specification is being considered by the OGC Membership to be approved as a formal OGC standard.
>  
> Regards
>  
> Carl Reed, PhD
> CTO and Executive Director Specification Program
> OGC
>  
> The OGC: Helping the World to Communicate Geographically
>  
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> <10-034r2_Moving_Object_Snapshot.zip>

George Percivall
Open Geospatial Consortium
http://www.opengeospatial.org/
E-mail: percivall@opengeospatial.org
Voice: +1-301-560-6439



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