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extend [2018/05/03 11:13]
brucemutton [Extended elevation scrap drawing considerations]
extend [2018/08/08 02:19] (current)
brucemutton [Extended elevation scrap drawing considerations] add -flip none
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 There should only be one '​start'​ specification I think, but there seems to be no ill effect if there are multiple starts.\\ There should only be one '​start'​ specification I think, but there seems to be no ill effect if there are multiple starts.\\
 \\ \\
-''​extend right <​leg>''​ - extend this leg only, to the right, then continue extending subsequent legs, left or right, as per the leg immediately previous.\\ +''​extend right <​leg>''​ - extend this leg only, to the right, then continue extending subsequent legs, left or right, as per the leg immediately previous. ​ But sometimes it continues generating all legs, as per the next entry below!\\ 
-''​extend right <​station>''​ - continue generating all extended centreline legs from this station onwards, towards the right. ​ Usually this option will not work as described, unless it is preceded by one or two extend right <leg> statements.\\+''​extend right <​station>''​ - continue generating all extended centreline legs from this station onwards, towards the right. ​ Usually this option will not work as described, unless it is preceded by one or two ''​extend right <leg>'' ​statements. ​ And sometimes it can appear to extend the wrong way.  If this happens, use ''​extend ... <​leg>''​ rather than ''​extend ... <​station>''​\\
 ''​extend left <leg> or <​station>''​ - same as for extend right, but extending left!\\ ''​extend left <leg> or <​station>''​ - same as for extend right, but extending left!\\
 \\ \\
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 ''​extend reverse <​station>''​ - continue generating all extended centreline legs from this station onwards, in the opposite direction to the leg immediately previous.\\ ''​extend reverse <​station>''​ - continue generating all extended centreline legs from this station onwards, in the opposite direction to the leg immediately previous.\\
 \\ \\
-''​extend vertical <​leg>''​ - do not extend this leg horizontally,​ extend only the vertical component of this leg, then continue extending subsequent legs as per leg immediately previous.\\+''​extend vertical <​leg>''​ - do not extend this leg horizontally,​ extend only the vertical component of this leg, then continue extending subsequent legs as per leg immediately previous. ​ The order of stations in your vertical statement should usually match the direction of extended elevation centreline generation. However if Therion seems to ignore this vertical statement, try reversing the order of the stations in your vertical statement, and it might work!\\
 ''​extend vertical <​station>''​ - continue generating only the vertical components all extended centreline legs from this station onwards.\\ ''​extend vertical <​station>''​ - continue generating only the vertical components all extended centreline legs from this station onwards.\\
 \\ \\
 ''​extend ignore <​leg>''​ - generation of extended centreline shall not take this leg, it will take the (an)other leg if possible.\\ ''​extend ignore <​leg>''​ - generation of extended centreline shall not take this leg, it will take the (an)other leg if possible.\\
   * If the leg is an open branch (does not loop back to the main centreline),​ then this has the effect of hiding the entire branch from this leg onwards, at this leg.   * If the leg is an open branch (does not loop back to the main centreline),​ then this has the effect of hiding the entire branch from this leg onwards, at this leg.
-  * If leg is part of a loop, a loop connection gap, with joining map-connection line will be formed between two instances of the first station in the leg specification.+  * If leg is part of a loop, it beaks the loop.  ie a loop connection gap, with joining map-connection line will be formed between two instances of the first station in the leg specification.
 The order of stations in your ignore statement should usually match the direction of extended elevation centreline generation. ​ However if Therion seems to ignore this ignore statement, try reversing the order of the stations in your ignore statement, and it might work!  Sometimes the leg specification needs to follow the direction of survey, if it differs from the current direction of extend generation.\\ The order of stations in your ignore statement should usually match the direction of extended elevation centreline generation. ​ However if Therion seems to ignore this ignore statement, try reversing the order of the stations in your ignore statement, and it might work!  Sometimes the leg specification needs to follow the direction of survey, if it differs from the current direction of extend generation.\\
 ''​extend ignore <​station>''​ - where <​station>​ is one leg past a junction in the direction of generation. ​ The generation of extended centreline shall not take this leg. I have found this syntax unreliable, and the following may explain why. Marco Corvi says (if I understand correctly) this does not work where there are only three legs meeting at a junction ie the usual case.  So only for use where 4 or more legs meeting at junction(?​). ''​extend ignore <​station>''​ - where <​station>​ is one leg past a junction in the direction of generation. ​ The generation of extended centreline shall not take this leg. I have found this syntax unreliable, and the following may explain why. Marco Corvi says (if I understand correctly) this does not work where there are only three legs meeting at a junction ie the usual case.  So only for use where 4 or more legs meeting at junction(?​).
 Also do not use this syntax where <​station>​ IS the junction station, obviously that will have unpredictable results. \\ Also do not use this syntax where <​station>​ IS the junction station, obviously that will have unpredictable results. \\
-Extend ​break is mentioned in some Therion posts, presumably as an alias for extend ignore (Survex terminology). ​ It will trigger a Therion error “unknown extend flag – break”.\\+<​del>''​extend ​break''</​del> ​is mentioned in some Therion posts, presumably as an alias for extend ignore (Survex terminology). ​ It will trigger a Therion error “unknown extend flag – break”.\\
 Sometimes branch centrelines will be ignored (hidden?) by default, and an extend right (or similar) statement will be required to stimulate it’s generation.\\ Sometimes branch centrelines will be ignored (hidden?) by default, and an extend right (or similar) statement will be required to stimulate it’s generation.\\
 \\ \\
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 ====Extended elevation scrap drawing considerations==== ====Extended elevation scrap drawing considerations====
-If you have drawn a scrap with the opposite orientation to the extended centreline generation, it will tend to plot inside out.  You need to compensate for this by including ''​-flip horizontal''​ in the definition of your scrap. ​ Or you can add ''​-revise scrap-id -flip horizontal''​ in your Extend-CaveName-ElevEXT.th file.+If you have drawn a scrap with the opposite orientation to the extended centreline generation, it will tend to plot inside out.  You need to compensate for this by including ''​-flip horizontal''​ in the definition of your scrap. ​ Or you can add ''​-revise scrap-id -flip horizontal''​ or ''​-flip none''​ in your Extend-CaveName-ElevEXT.th file.
  
 If you include in your scrap drawing a ''​point station -name <​station>''​ where that <​station>​ is at a survey leg junction AND is offset in the extended centreline due to extended loop misclosure, then it will force the extended station to plot, incorrectly,​ in its original location, distorting the scrap in the vicinity of that leg.  This can be vexing, as \\ If you include in your scrap drawing a ''​point station -name <​station>''​ where that <​station>​ is at a survey leg junction AND is offset in the extended centreline due to extended loop misclosure, then it will force the extended station to plot, incorrectly,​ in its original location, distorting the scrap in the vicinity of that leg.  This can be vexing, as \\
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