Artificial boundary lines appear in terrain

[MinusD]

Occasionally I end up with artificially straight line features in my terrain, when performing my relatively high-quality final renders.

Does this occur because I have over-stressed some terrain setting?

The attached image <TerrainAnomaly.jpg> illustrates the problem.
Dave

[Dune]

It looks like some mask is at work, but hard to tell without a tgd. Any chance of posting that?

[MinusD]

That is what puzzles me, I've used no image map masks.  The TGD file is attached, thank-you, Dune!

[Dune]

You have smoothing enabled in the first surface layer, and breakup (only breakup color) unchecked, so the tiny 1cm smallest size will be smoothed, resulting in very sharp peaks/valleys. Better not use smoothing function like that, or use a way bigger smallest size of the breakup fractal.
The third SL has the same issue, so I suggest rendering again with smoothing off, or at least checking what influence the breakup shader will have when 'only breakup color' is unchecked.

[MinusD]

Ah HA!  Terrific, thank-you!!
I have not found the Rosetta Stone for the myriad attributes contained in Terragen; more study on my part, and less instinctive tinkering may be warranted....    :  )
-d