[therion] Re: Help - my cave is inside-out

[Martin Budaj]

>> Now that I've drawn about 8km of survey the last scrap (top right hand
>> corner - scrap bmb3_s3) has had 'pillar failure' again.
>>
>> There are 3 pillars which do not work (the insides are filled). They are
>> all
>> walls with -outline in and I've tried reversing them, but it seems to stay
>> broken. What's going on?


There is another problem. Even if scrap boundary has correctly specified
all -outline out/in/none options, there may be problem to determine which
area is inside of the scrap if the outline crosses itself (like figure 8).
In such a case you get a MetaPost warning

Warning: scrap outline intersects itself in bmb3_s3 at fake

and it is than random if MetaPost determines the interior of scrap
correctly. The solution is to
1) find where the loop occured -- this may be tricky, but start with the
endpoints where scraps should join. The loop may be very small, even
unnoticable. Even worse, it may not be visible at all, because it happens
anly after the joining of scraps -- which is the case of your example  :(
2) correct the position of the control points (see the second picture)

I hope the enclosed pictures make it more clear.

Regards
Martin