| Re: Switch: usage of attribute @course [message #1751 is a reply to message #1707] |
Thu, 05 April 2018 17:38   |
Thomas Nygreen JBD
Messages: 68
Registered: February 2017
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Member |
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Dear all,
christian.rahmig wrote on Wed, 05 April 2017 12:51The question:
I want to ask you if you understand the current implementation /
understanding of railML track connection modelling or whether you
support to change it in the future? Shall the choice of value for
@course depend on the orientation of the track or shall it be
independent and just linked with the construction layout of the switch?
I find the current implementation, described in [1] to be good, and I strongly suggest keeping it.
On the other hand, I find the wiki page for the switch/connection element to be lacking, with no description of the reference frame for what is left and right. I suggest adding something like "as seen in the up direction", as well as a link to [1]. It would also be interesting to know how many software implementations follow the current interpretation and how many that don't. Notably, the current "railML Simple Example by railML.org" [2] does not.
christian.rahmig wrote on Wed, 05 April 2017 12:51The problem:
The attribute @course may have the values "left", "right" and
"straight". However, the choice of this value currently depends on the
orientation of the track where the switch is located. The wiki page [1]
shows this in four small figures (examples 1-4). Consequently, the same
type of switch (with respect to its construction layout) may define its
branch one time with course="left" and the other time with
course="right" depending on the different orientation of the track where
the switch is located.
It is a bit odd to argue that it is a disadvantage that the @course changes when the orientation of the track does, as that is the case for important attributes of most elements, most notably @dir. As the "up" direction is the main reference for everything else, it seems most reasonable to use the same reference for @course. Changing "left" to "right" for @course is no more difficult than it is for platformEdge/@side. It is also an advantage to have connection/@course = "right" and platformEdge/@side = "right" actually being the same side of the track.
Regarding the fact that the same geometry can result in different topological descriptions: that is the case even if we flip the reference frame for @orientation="incoming".
christian.rahmig wrote on Wed, 05 April 2017 12:51Please also consider the forum post by Claus Feyling on this matter (see [3]).
I have read Claus Feyling's post, and, as I have argued above, I disagree with the proposal to change the interpretation of @course. Also, I am not convinces about the need for @geometry, as it in most cases follows from the topology, and in remaining cases, such as the one he gives, can be described by switch/@trackContinueRadius and connection/@radius. Although, as the attachments are missing, there could be something I am missing.
[1] https://wiki.railml.org/index.php?title=Dev:Connection_betwe en_tracks
[2] https://www.railml.org/en/user/exampledata.html
[3] https://www.railml.org/forum/index.php?t=msg&th=516
Best regards
Thomas
Best regards,
Thomas Nygreen
Railway capacity engineer
Jernbanedirektoratet
[Updated on: Mon, 09 April 2018 13:09] Report message to a moderator |
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