Differences

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--- faq [2018/05/08 11:11] – [Why do peoples names sort alphabetically when they used to sort by length of cave explored and surveyed?] brucemutton
+++ faq [2019/05/01 14:26] – More causes for self-intersecting scrap outlines tarquinwj
@@ Line 740: / Line 740: @@
 (There are some other scrap drawing tips in [[tips#avoiding_invisible_or_misshapen_scraps_in_loch_and_google_earth|Avoiding Invisible or Misshapen Scraps in Loch and Google Earth]])
+This warning can sometimes happen if you have two wall lines joining on a single point, where Bézier curve controls pull the lines into a very acute angle (where the "back" facing Bézier controls are pulled beyond the arc of the other line). The solution is to reduce the angle of the join, or insert more linepoints so that the angle can be produced without needing to use Bézier controls to pull the lines so far that Metapost thinks they overlap. Check any such places in your scrap outline, and test whether removing the Bézier back or forward controls fixes it. If so, then this is the location of your error.
+It can also happen if you have inserted a point along a wall line, with its Bézier controls oriented backwards compared with the rest of the line, so that the backwards one points forwards, or vice versa. The rendering looks normal, but Metapost has had to flip the orientation of the line twice, so it complains.
+It can also happen if you have accidentally added two linepoints at the same location - this also causes Metapost to flip directions in order to get from one point to the next. Step through each linepoint in turn (in the "Lines" section of XTherion), and see if two ended up in the same place.
+It can also happen on a closed wall line, when the ends join, and you pull the wrong Bézier control past the junction - this causes a combination of the two problems mentioned above.
 ====What are the limits for map and for atlas PDFs?====