[Therion] Cross section line error

[Andrew Atkinson]

On returning from today's trip and duly settling down to draw up the 
survey I go the error below.

Well it did not give me many clues, but eventually found the problem. I 
had drawn a cross section line, and then clicked closed, somehow, which 
gave a double line. (Having 3 points and closed does not seem to cause 
the error)

Anyway, I was hoping that if I sent this maybe it would be possible to 
say in the error message what caused the error, even if it was only a 
line number from the th2 file, or the type of line, possibly it does and 
I jsut do not know how to read it. Luckily this is a small file so it 
was easy to delete things until it worked.
Attached is the file with the error within it. It is the section line 
for section PalmersSX1.2,

#################### end of cavern log file ####################
done
calculating basic statistics ... done
processing extended elevation ... done
processing references ... done
selecting export objects ... done
processing projection plan ... done
average distortion: 0.09%
writing Palmers.pdf ...
processing projection none ... done
####################### metapost log file ########################
This is MetaPost, version 1.208 (kpathsea version 5.0.0) (mem=mpost 
2011.10.19)  12 NOV 2011 18:46
**data.mp
(./data.mp [4001] [4002] [4003] [4004] [4005] [4006] [4007] [4008] 
[4009] [4010
] [4011] [4012]
[1] [2]
! angle(0,0) is taken as zero.
<for(0)> ...rotated.angle(thdir(Q,(EXPR0)))shifted
 
(point(EXPR0)of.Q);pickup....

l_section->...(0.1u,0.55u);fi;exitif.pnt=-1;endfor
                                                   ;
l.5349 ),0,2)
              ;
The `angle' between two identical points is undefined.
I'm zeroing this one. Proceed, with fingers crossed.

! angle(0,0) is taken as zero.
<for(2)> ...rotated.angle(thdir(Q,(EXPR0)))shifted
 
(point(EXPR0)of.Q);pickup....

l_section->...(0.1u,0.55u);fi;exitif.pnt=-1;endfor
                                                   ;
l.5349 ),0,2)
              ;
The `angle' between two identical points is undefined.
I'm zeroing this one. Proceed, with fingers crossed.

[3] [4] [5] [6] [7] [8] [9] [10] [11] (./mptextmp.mp) (./mptextmp.mp)
(./mptextmp.mp) (./mptextmp.mp) (./mptextmp.mp) (./mptextmp.mp) [12] 
[13] [14]
[15] [16] [17] [18] [19] [20] [21] )

Here is how much of MetaPost's memory you used:
  1019 strings out of 1162
  12416 string characters out of 15838
  60569 words of memory out of 3000000
  1320 symbolic tokens out of 16384
  9i,75n,12p,199b,4f stack positions out of 300i,84n,10000p,200b,15f
  51 string compactions (moved 448697 characters, 36984 strings)
33 output files written: data.1 .. data.4012

#################### end of metapost log file ####################
therion: error -- metapost exit code -- 512
writing xtherion file ... done
therion: warning -- error deleting temporary directory -- /tmp/th4359
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