Skipping sections of a layer and then filling in....why?

[billshook 0]

Cura does this in lines as well, but I thought concentric is the easiest photo to show what I'm talking about.    What I'm showing is the second layer of plate and it's printed with concentric lines.   Starts in the middle and works its way out in a spiral.   The oddity is when it skips a single line a third of the way out and then skips a chunk of lines, then finishes all the way out...and skips back to fill in the lines it skipped.   This always creates a bit of a difference in the look of the layer.  Is there a setting I have not found to prevent this?   This model is the perfect example as their is nothing to cause the skip.  It's just a big flat area and yet for reasons I can't explain Cura skips around on it.  The real issue of course is when it's done in top layers as it can ruin what should be a great look.   it's entirely possible there is a setting I have not yet found to prevent this.   Any thoughts would be appreciated.

[electric_monk 0]

I'm having this exact problem with a model with a large flat rectangular base - it skips a chunk in the middle as it's doing all the parallel lines and then comes back for it. Seems a very eccentric thing for the program to do.

[gr5 2,177]

screenshot please.  You can use the horizontal slider to make it obvious which section it is skipping.

 

Keep in mind that minimizing the travels is a complicated business.  Trying every combination of which lines to do in which order to see which is the fastest will usually take more computing cycles than would be possible to do in less than a minute even if you had the computing power of every computer on the planet.  Even if every atom in the universe was as powerful as your computer, it would probably take longer than the age of the universe.  This is common.  What seems simple actually is a difficult problem.  This problem actually has a name: "the travelling salesman problem" and there are many algorithms that come close to the best possible solution but none of them guarantee the best solution and as you saw yourself, some solutions seem pretty obviously *not* the fastest solution.  But humans are better at some tasks than computers.

 

This algorithm has to run 1000 times if you have 1000 layers sliced and people get upset if it takes an hour to slice their part so a compromise was made.  I agree that a better algorithm could be chosen but this is not easy to do.

[GregValiant 1,260]

In the situation of the concentric pattern, it just seems to make sense to continually move a line width at a time and draw the next circle (as separate line segments of course).  I understand there are a lot of computations going on in the background (every atom in the universe?) but the final decision that it is better to move outboard and then come back in doesn't add up.

If Cura would just play the CD it would be good.  Instead, it plays tracks 1 to 4, skips 5, plays 6 to 10 and then plays track 5 backwards.  Effectively it makes the total travel longer than would be necessary to play 1 thru 10.  Playing a track backwards might have been OK for the Beatles, but it doesn't do much for me now.

[gr5 2,177]

Typically when it finishes one "line" or "trace" I think it usually moves to the nearest line to do next.  Because lines finish far from where they start (typically), the closest line to do next might be a bad choice.

[GregValiant 1,260]

I understand when it does it with rectangular areas with holes in them.  I only used Concentric once and found the behavior odd.  Since it really can't be concentric (because there are only line segments) - what you say about end points may be it.  A spiral pattern would work but probably be of limited use.  With a hole in the surface the path would be different anyway.