23. 9. 2019 v 1:08, Bruce Mutton <bruce@tomo.co.nz>:

To ‘compensate’ by reversing lines may result in a project that plots incorrectly when you toggle to another symbol set (I occasionally produce both NZSS and UIS versions of maps, and these have the opposite convention). It also tends to destroy loch models, as line:pit orientation governs model generation, and chimney and meander etc could potentially in the future. Passage shading in pdf outputs can be affected to.

There is one basic principle of using Therion for map production: One doesn’t draw map In Therion, but „construct“ it instead.

The yellow tick on line shows the „empty space side“ (and beginning of line) of line symbol in case mentioned in https://therion.speleo.sk/wiki/drawingchecklist#wall . This information is used for generation of loch models and others as Bruce mentioned. The orientation of small ticks on line symbol „ceiling step“ depends on definition of line symbol itself in particular symbol set.

So correct way is to draw line symbol „ceiling step“ with orientation of yellow tick to „empty space“ and use symbol line „ceiling step“ representation you want. With small ticks in the same direction as yellow tick or in opposite direction.

Martin