S&C Design Difference Between Tunout and Switch in Library

Question

Hi all 
 I am slowly tying to teach myself S&C design through Power Rail. 
 After some help from people on this forum I managed to get hold of the S&C library for the UK 113A. 
 I have reviewed the library in conjunction with the track design handbook. 
 My question is that the library contains two different types of layouts either:- 
 - [Begin Turnout] and [End Turnout] 
 - [Begin Switch] and [End Switch] 
 What is the difference between the two? 
 I have copied and pasted an example of the two types from the library for reference. 
 Can anyone help? 
 [Begin Turnout] 
 [Name] = "NR56 CV 10" 
 [Description] = "NR56 CV 10" 
 [Switch Annotation] = "" 
 [Crossing Annotation] = "" 
 [Type] = "single" 
 [Begin Branch] 
 [Theoretical .1 to .1] = 1.615104 
 [Length Along Mainline] = 25.555683 
 [Triangle] = 14.319986 
 [Ratio at .0] = 9.975000 
 [Begin Branch Data] 
 13.502503 245.051000 245.051000 
 13.645801 304.485000 304.485000 
 [End Branch Data] 
 [Leading Linear] = "FALSE" 
 [End Branch] 
 [Turnout Bending Method] = "default" 
 [Along Inner Rail] = "TRUE" 
 [Along Outer Rail] = "FALSE" 
 [Last Element Unbent] = "FALSE" 
 [End Turnout] 
 
 [Begin Switch] 
 [Name] = "NR56 CV 10 Straight" 
 [Description] = "NR56 CV 10 Straight" 
 [Fundamental Type] = "STRAIGHT" 
 [Switch Annotation] = "CVS STR" 
 [Crossing Annotation] = "10" 
 [Type] = "S&C / single" 
 [Gauge] = 1.432000 
 [Crossing Angle] = 10.000000 
 [Front Length] = 3.070000 
 [Mainline Heel Length] = 0.000000 
 [Turnout Heel Length] = 0.000000 
 [Nominal Switch Radius] = 245.767000 
 [Nominal Turnout Radius] = 245.767000 
 [Lead Length] = 24.957000 
 [Crossing IP to Nose] = 0.160000 
 [MP to RP] = 0.000000 
 [Distance to Last Long Sleeper] = 0.000000 
 [Flexible] = "TRUE" 
 [Begin Tangent Offset Data] 
 3.070000 0.000000 0.0090713453 287.251440 
 4.069941 0.010812 0.0125526159 287.251440 
 5.069838 0.025105 0.0160338866 287.251440 
 6.069680 0.042878 0.0195151572 287.251440 
 7.069454 0.064132 0.0229964278 287.251440 
 7.320581 0.070018 0.0238709116 245.767000 
 8.069143 0.089031 0.0269177131 245.767000 
 9.068723 0.117980 0.0309866076 245.767000 
 10.068177 0.150995 0.0350555022 245.767000 
 11.067489 0.188076 0.0391243967 245.767000 
 12.066641 0.229223 0.0431932912 245.767000 
 13.065618 0.274436 0.0472621857 245.767000 
 14.064402 0.323712 0.0513310802 245.767000 
 15.062978 0.377052 0.0553999748 245.767000 
 16.061328 0.434455 0.0594688693 245.767000 
 17.059437 0.495920 0.0635377638 245.767000 
 18.057287 0.561445 0.0676066583 245.767000 
 19.054863 0.631030 0.0716755529 245.767000 
 20.052147 0.704673 0.0757444474 245.767000 
 21.049123 0.782373 0.0798133419 245.767000 
 22.045774 0.864130 0.0838822364 245.767000 
 23.042085 0.949941 0.0879511309 245.767000 
 24.038038 1.039805 0.0920200255 245.767000 
 25.033618 1.133721 0.0960889200 245.767000 
 25.969871 1.225771 0.0999168068 0.000000 
 26.028808 1.231679 0.0999168068 0.000000 
 27.023820 1.331430 0.0999168068 0.000000 
 28.018833 1.431181 0.0999168068 0.000000 
 29.013845 1.530931 0.0999168068 0.000000 
 30.008858 1.630682 0.0999168068 0.000000 
 31.003870 1.730433 0.0999168068 0.000000 
 31.998882 1.830183 0.0999168068 0.000000 
 32.993895 1.929934 0.0999168068 0.000000 
 33.988907 2.029684 0.0999168068 0.000000 
 34.983920 2.129435 0.0999168068 0.000000 
 35.978932 2.229186 0.0999168068 0.000000 
 36.973945 2.328936 0.0999168068 0.000000 
 37.968957 2.428687 0.0999168068 0.000000 
 38.963970 2.528438 0.0999168068 0.000000 
 39.958982 2.628188 0.0999168068 0.000000 
 40.953995 2.727939 0.0999168068 0.000000 
 41.949007 2.827690 0.0999168068 0.000000 
 42.944020 2.927440 0.0999168068 0.000000 
 43.939032 3.027191 0.0999168068 0.000000 
 44.934045 3.126941 0.0999168068 0.000000 
 45.929057 3.226692 0.0999168068 0.000000 
 46.924069 3.326443 0.0999168068 0.000000 
 47.919082 3.426193 0.0999168068 0.000000 
 48.914094 3.525944 0.0999168068 0.000000 
 49.909107 3.625695 0.0999168068 0.000000 
 50.904119 3.725445 0.0999168068 0.000000 
 51.899132 3.825196 0.0999168068 0.000000 
 52.682000 3.903679 0.0999168068 0.000000 
 [End Tangent Offset Data] 
 [Begin Extended Data] 
 [End Extended Data] 
 [End Switch]

Alastair Hume · Accepted Answer

I have not seen this before. 
I have had a look into 113A library showing both Turnouts and Switches. It seems to me that Turnouts are based on true geometry and switches are based on lots of small joined up lines. 
 
So turnouts actually place tangental elements, curves, transitions and straights, in the drawing as graphics, but swiches do it a bit differently. 
 
It looks like swithes are based on a chainage, offset and instantanious radius (including planing radius) from the start of the turnout fronts or origin. I see there is a 3.070m dimension, which is usually the switche fronts. The switche definition seems to talk in railways terms with Lead Length and Crossing IP to Nose etc instead of the triangle length and .1 .2 .3 terms used in turnout createion. 
 
Let me know how your testing turns out. 
 
A

jpln · Answer

This is the difference between Turnouts and Switches definition. As Alastair explained, turnouts are using true geometry whereas switches s are using tangent and offset value. Switches are mainly used in UK. I think it is the legacy method but I didn't work much with UK turnouts. I did for HS2 but using turnouts definition.

Paul Bennett · Answer

As has been mentioned above, the 'distance & offset' switch library was the original UK library and was pretty much a direct conversion of the MX Rail switch library. 
 
A few years ago Network Rail published an official suite of true geometry libraries, available to download on their Standards Design Catalog, which I'm guessing is where you got your [Begin Turnout] example above. Because these libraries have been validated by Network Rail and published as RE/PW files (RE/PW/1205 & RE/PW/1215 for the text version, RE/PW/1206 & RE/PW/1216 for the XML version), these are the ones that should be used. I understand these have superseded the 'distance & offset' switch library.

Alastair Hume · Answer

The planing radius is the radius of the ironwork from the physical switch toe. It starts at a distance "T" from the Origin of the switch radius at the switch toe. It has a flatter radius than the switch radius for a certain planing length. This planing radius is not tangential to the through route of the turnout. In real life, the switch cannot be tangential truly due to widths of rail and limitations of ironwork, so planing must occur. 
 
I would guess the fact that it isn't tangential is the reason why it is not included in the true geometry type turnout.

Paul Bennett · Answer

Alastair's right, the turnouts only model the tangential geometry. 
 Have a look at RE/PW drawings 1204 and 1214, these explain how the turnouts have been set up and confirm the planing radius is not modelled. 
 Here's an extract from RE/PW/1204 - 
 
 .