some thoughts about train track part origin choices

[Steffen]

At part
http://www.ldraw.org/cgi-bin/ptdetail.cg.../85977.dat
some questions arose about where to put the origin of train track parts.

The X and Z choice usually is not a problem, both for curved or straight parts:
we there can simply follow the principles of our usual practice, i.e. "part center".
This is also what existing parts do, e.g. 3229a.dat, 3229ac01.dat, 3229ac04.dat.

Regarding the Y origin, there is the question
"Should the origin be (A) at the top of the studded sleepers or (B) at the top of the rails?"
The current status in the library needs to be explained historically:
The rail parts e.g. 3229a.dat existed in the library long time already.
As usual for parts, they had their origin at the top.
This origin was kept when 3229ac01.dat was created, an assembly of two curved rails.
This origin was kept when 3228ac02.dat was created, an assembly of two straight rails.
This origin was kept when 3228bc02.dat was created, an assembly of two straight rails plus sleeper.
This origin was kept when 948ac02.dat was created, a point.
This is the 4.5V blue and grey rails story.
The same origin was applied to the analogous 12V blue and grey rails, e.g. 73696c04.dat.

So to make a long story short: carrying over the origin choice of the single rail part to the rails assemblies
led to the effect that the vertical origin of all 4.5V and 12V train track parts and assemblies is at the top of the rails.

The origin question now again arises for the 9V train track.
http://www.ldraw.org/cgi-bin/ptreviewsum...aintrack9v
(with or without metal top), and for other train tracks where the rails are firmly attached to the sleepers.
There the question is if the vertical origin should be
(A) at the top of the sleepers or
(B) at the top of the rails.
Both solutions have advantages and disadvantages:
Solution (A) would make the new train track parts better match plates.
Solution (A) would be the intuitive one if one did not know about existing train track parts.
Solution (B) would make the new train track parts better match existing train track parts.
Both solutions are no problem for train track layout software like BlueBrick.

So what to do now? Current situation:
- Official train track parts out in the wild have "origin at rail top".
- *SOME* of newer train track parts with "origin at sleeper top" already "sneaked" out, e.g. 32087.dat
- all newer train track parts currently on the PT like 74746.dat or 53401.dat or 85976.dat follow the "origin at sleeper top" strategy

I have no real strong opinion here. We could opt for one of these solutions:
(i) make all train track parts have origin at rail top
(ii) make all train track parts have origin at sleeper top
(iii) let some have it this way, others the other way

Solution (i) would require to re-position official file 32087.dat.
Solution (ii) would require to re-position many official 4.5V and 12V files
Solution (iii) would create inconsistency but would minimize current trouble

After having written this, I slightly tend to solution (iii)...

[Philippe Hurbain]

After having written this, I slightly tend to solution (iii)...

Often writing things down makes solution appear... (iii) is the best for me too, followed by (ii) that is more "logical" but causes so much trouble!

[Michael Heidemann]

And why not using your solution (i). As far as I understand there is currently only one part that needs our attention (and of course those on the PT).
With solution (i) we have a straightforward (but not the best) solution for all those parts without much trouble.

[Steffen]

yes, to me (iii) is the one with the least effort,
followed by (i) which brings largest consistency by just touching 1 official part

[Ronald Vallenduuk]

I just had a quick look through some parts and it seems to me that the tradition is more 'origin at the highest surface with studs' than 'origin at part top'.
See for example:
40996 Brick 1x4 with Sloped Ends and Two Top Studs
50948 Slope Brick 3 x 4 x 0.667 Curved with 2 x 2 Cutout
50967 Slope Brick Curved 8 x 1 x 1 & 2/3 with Arch
41766 Slope Brick Curved 8 x 2 x 2
98284 Plate 2 x 2 Round with Hole and 4 Vertical Bars
4623 Plate 1 x 2 with Vertical Bar on Long Side and Long Arm
512 Electric Train 12V Level Crossing Sign
3218 Train Direction Switch - 4.5 Volt
4169 Train Signal Stand

And there are many more. 512 has a completely strange origin and orientation by the way. And with train parts like 3218 and 4169 having their origin at the top of the plate I would even argue that the 4.5V and 12V track assemblies are the parts with the inconsistent origin...

I would favour keeping the origin for 9V track parts at the top of the plate (sleeper).

I would have no problem with the little inconsistency it would cause. Despite our best efforts the catalog is full of them. For example the slopes mentioned above have their origin on top of the highest plate, with the top of the part another plate height above. These parts however have a very similar shape but have their origin at the top of the curve:
6005 Arch 1 x 3 x 2 with Curved Top
6091 Brick 2 x 1 x 1 & 1/3 with Curved Top

[Steffen]

I agree.
"At sleeper plate top" is perfectly fine for me.
BlueBrick anyway has the option of specifying a vertical offset in its xml files.