Ok, last reply to myself for today :)I think I got it now. The original algorithm suggested by Lee is most likely correct. There is one important addition though. Lee wrote that the bit field looks like this 1:11:1:11, where the two 1 bits (bit 0 and 12) have to be 0. This seems to be true for bit 12 (I have only tried two files so it is still possible that bit 12 can be 1. However, bit 0 can be 1 and often is indeed 1 in the hydroline files. It works like the width flag in the 'parent' point. If it is one a width entry follows. This is used to have a variable width in between child points. Whew. After all this time, it seems that the mysteries of line structure have now truly been solved.Thanks Lee, without your contribution I don't know if I would have figured it out.Time for a drink... :-beerchugCheers, Christian

Hi ChristianI