Re: [CF-metadata] Platform Heave
Jonathan, Two out of three of Nan's "most intuitive" rotations (pitch and yaw) are clockwise rather than anticlockwise if the unit vectors are X-fore, Y-port, and Z-up, which form a right-hand coordinate system. This is part of why you will see examples where the unit vectors are defined as X-fore, Y-starboard, and Z-down. This orientation of the unit vectors makes yaw to starboard, pitch up, and roll starboard down all anticlockwise rotations, but it points the Z unit vector down, which is, for most people, rather counter-intuitive. And this is why we are trying to define things in terms that don't require specification of unit vector directions. I'm going to try to continue down that path and avoid calling out clockwise/anticlockwise. Grace and peace, Jim On 9/4/18 10:18 AM, Jonathan Gregory wrote: Dear Jim If that's the general consensus, then we can go that general direction. I'll prepare pairs of everything. Thank you for your flexibility. Regarding Nan's suggestions for names - I'm not a "ship person" so starboard and port are unfamiliar terms that I have to constantly check myself on. I dislike putting them in the names. I don't see them in regular use in the satellite domain. The same goes for bow as far as usage outside of the ship domain. Airplanes have noses. Satellites have ... I don't know if there is even a name, as there is no need for a leading edge. I'll struggle to find something, and then we can wrangle over it. I agree with you - it would be better to have something generic and self- explanatory, even if it diverges from familiar terminology. I think the "most intuitive" way to represent the angles - and most consistent as well, in my view - is clockwise rotations around the unit vectors. This makes positive yaw to starboard, positive pitch nose up, and positive roll starboard up. But we are talking about having both signs represented in names, so I guess that is moot. I agree with this too. For describing polygonal bounds, we say that the vertices should be traversed anticlockwise as seen from above. That is a positive direction of rotation around the vertical axis, since longitude- latitude-upward is a right-handed coordinate system. I suppose this is the yaw rotation - but is that the opposite sign from yours? Best wishes Jonathan On 9/3/18 12:51 PM, Jonathan Gregory wrote: Dear Roy and Nan I agree that if there are existing names whose sign convention is undefined we can't retrospectively define it. I think those ones ought to be deprecated, though, in favour of new ones with signs indicated. Best wishes Jonathan - Forwarded message from Nan Galbraith - Date: Sun, 02 Sep 2018 11:57:33 -0400 From: Nan Galbraith To: "Lowry, Roy K." Cc: cf-metadata@cgd.ucar.edu Subject: Re: [CF-metadata] Platform Heave User-Agent: Internet Messaging Program (IMP) H4 (5.0.23) I second Roy's suggestion; existing names have undefined directionality, and new names have explicit directions. This seems like the only way to move forward. If there's a difference of opinion on which direction should be in the new name, we can easily create a pair for each term. What would the explicit names be? Some of the terms in the thread below use 'right' and 'left' where 'port' and 'starboard' might be more clear, since, as Roy points out, left and right can be taken as 'looking forwards from the platform or looking at the front of the platform.' I also agree that these are the most intuitive way to represent these angles/motions: heave positive up pitch positive bow up yaw positive to starboard roll positive starboard side down Would the names be something like heave_up, pitch_bow_up, yaw_to_starboard, and roll_to_starboard? We do need to differentiate these from the exiting names. Regards - Nan Quoting "Lowry, Roy K." : Dear Jim, >From my researches into existing oceanographic data sets (SeaDataCloud holdings plus EU glider data projects), covering heave, pitch, roll and yaw. I haven't discovered a single deviation from the conventions: heave positive up Pitch positive bow/nose up yaw positive to starboard roll starboard side down I have yet to find any data sets, other than those described by Ken in these discussions, in my searches containing surge or sway. The only ambiguity I have found in the wider domain of Google is where the concept of 'positive clockwise' has been used without specifying whether the observer is looking forwards from the platform or looking at the front of the platform. This isn't helped by the multitude of bidirectional vectors (arrows at each end) in illustrative diagrams. Might our lives be made easier if we adopted a set of conventions, state them explicitly in the Standard Names as Jonathan suggests leaving room in the unlikely - in my view at least - event of Standard Names for the opposite convention being required? Cheers, Roy. I have now retired but will continue to be active through an Emeritus Fellowship usi
Re: [CF-metadata] Platform Heave
Dear Jim > If that's the general consensus, then we can go that general > direction. I'll prepare pairs of everything. Thank you for your flexibility. > Regarding Nan's suggestions for names - I'm not a "ship person" so > starboard and port are unfamiliar terms that I have to constantly > check myself on. I dislike putting them in the names. I don't see > them in regular use in the satellite domain. The same goes for bow > as far as usage outside of the ship domain. Airplanes have noses. > Satellites have ... I don't know if there is even a name, as there > is no need for a leading edge. I'll struggle to find something, and > then we can wrangle over it. I agree with you - it would be better to have something generic and self- explanatory, even if it diverges from familiar terminology. > I think the "most intuitive" way to represent the angles - and most > consistent as well, in my view - is clockwise rotations around the > unit vectors. This makes positive yaw to starboard, positive pitch > nose up, and positive roll starboard up. But we are talking about > having both signs represented in names, so I guess that is moot. I agree with this too. For describing polygonal bounds, we say that the vertices should be traversed anticlockwise as seen from above. That is a positive direction of rotation around the vertical axis, since longitude- latitude-upward is a right-handed coordinate system. I suppose this is the yaw rotation - but is that the opposite sign from yours? Best wishes Jonathan > > On 9/3/18 12:51 PM, Jonathan Gregory wrote: > >Dear Roy and Nan > > > >I agree that if there are existing names whose sign convention is undefined > >we can't retrospectively define it. I think those ones ought to be > >deprecated, > >though, in favour of new ones with signs indicated. > > > >Best wishes > > > >Jonathan > > > >- Forwarded message from Nan Galbraith - > > > >>Date: Sun, 02 Sep 2018 11:57:33 -0400 > >>From: Nan Galbraith > >>To: "Lowry, Roy K." > >>Cc: cf-metadata@cgd.ucar.edu > >>Subject: Re: [CF-metadata] Platform Heave > >>User-Agent: Internet Messaging Program (IMP) H4 (5.0.23) > >> > >>I second Roy's suggestion; existing names have undefined directionality, > >>and new names have explicit directions. This seems like the only way to > >>move forward. If there's a difference of opinion on which direction > >>should be in the new name, we can easily create a pair for each term. > >> > >>What would the explicit names be? Some of the terms in the thread > >>below use 'right' and 'left' where 'port' and 'starboard' might be > >>more clear, since, as Roy points out, left and right can be taken > >>as 'looking forwards from the platform or looking at the front of > >>the platform.' > >> > >>I also agree that these are the most intuitive way to represent these > >>angles/motions: > >>>heave positive up > >>>pitch positive bow up > >>>yaw positive to starboard roll positive starboard side down > >>Would the names be something like heave_up, pitch_bow_up, yaw_to_starboard, > >>and roll_to_starboard? We do need to differentiate these from the exiting > >>names. > >> > >>Regards - Nan > >> > >>Quoting "Lowry, Roy K." : > >> > >>>Dear Jim, > >>> > >>> > From my researches into existing oceanographic data sets > (SeaDataCloud holdings plus EU glider data projects), covering > heave, pitch, roll and yaw. I haven't discovered a single > deviation from the conventions: > >>> > >>>heave positive up > >>> > >>>Pitch positive bow/nose up > >>> > >>>yaw positive to starboard > >>> > >>>roll starboard side down > >>> > >>> > >>>I have yet to find any data sets, other than those described by > >>>Ken in these discussions, in my searches containing surge or sway. > >>> > >>> > >>>The only ambiguity I have found in the wider domain of Google is > >>>where the concept of 'positive clockwise' has been used without > >>>specifying whether the observer is looking forwards from the > >>>platform or looking at the front of the platform. This isn't > >>>helped by the multitude of bidirectional vectors (arrows at each > >>>end) in illustrative diagrams. > >>> > >>> > >>>Might our lives be made easier if we adopted a set of conventions, > >>>state them explicitly in the Standard Names as Jonathan suggests > >>>leaving room in the unlikely - in my view at least - event of > >>>Standard Names for the opposite convention being required? > >>> > >>> > >>>Cheers, Roy. > >>> > >>> > >>>I have now retired but will continue to be active through an > >>>Emeritus Fellowship using this e-mail address. > >>> > >>> > >>> > >>>From: CF-metadata on behalf of > >>>Jim Biard > >>>Sent: 31 August 2018 14:38 > >>>To: cf-metadata@cgd.ucar.edu > >>>Subject: Re: [CF-metadata] Platform Heave > >>> > >>> > >>>Jonathan, > >>> > >>>That's only part of the issue. Here are the issues as I see them. > >>> > >>> * There is no single sign convention being followed in > >>>existing datasets
Re: [CF-metadata] Platform Heave
Hi. If that's the general consensus, then we can go that general direction. I'll prepare pairs of everything. Regarding Nan's suggestions for names - I'm not a "ship person" so starboard and port are unfamiliar terms that I have to constantly check myself on. I dislike putting them in the names. I don't see them in regular use in the satellite domain. The same goes for bow as far as usage outside of the ship domain. Airplanes have noses. Satellites have ... I don't know if there is even a name, as there is no need for a leading edge. I'll struggle to find something, and then we can wrangle over it. I think the "most intuitive" way to represent the angles - and most consistent as well, in my view - is clockwise rotations around the unit vectors. This makes positive yaw to starboard, positive pitch nose up, and positive roll starboard up. But we are talking about having both signs represented in names, so I guess that is moot. Grace and peace, Jim On 9/3/18 12:51 PM, Jonathan Gregory wrote: Dear Roy and Nan I agree that if there are existing names whose sign convention is undefined we can't retrospectively define it. I think those ones ought to be deprecated, though, in favour of new ones with signs indicated. Best wishes Jonathan - Forwarded message from Nan Galbraith - Date: Sun, 02 Sep 2018 11:57:33 -0400 From: Nan Galbraith To: "Lowry, Roy K." Cc: cf-metadata@cgd.ucar.edu Subject: Re: [CF-metadata] Platform Heave User-Agent: Internet Messaging Program (IMP) H4 (5.0.23) I second Roy's suggestion; existing names have undefined directionality, and new names have explicit directions. This seems like the only way to move forward. If there's a difference of opinion on which direction should be in the new name, we can easily create a pair for each term. What would the explicit names be? Some of the terms in the thread below use 'right' and 'left' where 'port' and 'starboard' might be more clear, since, as Roy points out, left and right can be taken as 'looking forwards from the platform or looking at the front of the platform.' I also agree that these are the most intuitive way to represent these angles/motions: heave positive up pitch positive bow up yaw positive to starboard roll positive starboard side down Would the names be something like heave_up, pitch_bow_up, yaw_to_starboard, and roll_to_starboard? We do need to differentiate these from the exiting names. Regards - Nan Quoting "Lowry, Roy K." : Dear Jim, >From my researches into existing oceanographic data sets (SeaDataCloud holdings plus EU glider data projects), covering heave, pitch, roll and yaw. I haven't discovered a single deviation from the conventions: heave positive up Pitch positive bow/nose up yaw positive to starboard roll starboard side down I have yet to find any data sets, other than those described by Ken in these discussions, in my searches containing surge or sway. The only ambiguity I have found in the wider domain of Google is where the concept of 'positive clockwise' has been used without specifying whether the observer is looking forwards from the platform or looking at the front of the platform. This isn't helped by the multitude of bidirectional vectors (arrows at each end) in illustrative diagrams. Might our lives be made easier if we adopted a set of conventions, state them explicitly in the Standard Names as Jonathan suggests leaving room in the unlikely - in my view at least - event of Standard Names for the opposite convention being required? Cheers, Roy. I have now retired but will continue to be active through an Emeritus Fellowship using this e-mail address. From: CF-metadata on behalf of Jim Biard Sent: 31 August 2018 14:38 To: cf-metadata@cgd.ucar.edu Subject: Re: [CF-metadata] Platform Heave Jonathan, That's only part of the issue. Here are the issues as I see them. * There is no single sign convention being followed in existing datasets "in the wild". * There is a long-standing convention for vertical coordinates using the attribute positive rather than having pairs of standard names for height_positive_up, height_positive_down, etc. The suggested solution is corollary, and the positive attribute could be used instead of adding a new attribute named direction with a suitable expansion of possible valid values. * In order to cover all bases, we'd need three versions for each standard name (e.g. - platform_roll, platform_roll_clockwise, platform_roll_anticlockwise - or similar names) * Having three different versions of each standard name will lead to new possibilities for getting things wrong by picking the wrong version. * Semantically, there is only one concept in each case. If I am searching for roll variables and I have multiple names that mean roll, I must expand my search to include all variants. This is a small example, but there are other examples of this problem that are definitel
