Uderwater terraforming

Apologies if this has been asked elsewhere.

Technically, land on private island sims can be raising lowered +/- 100m from currnt mean land surface level.

On my current sim, roughly 50% of the land above water is at 20m, which pitches the mean land height at somewhere between the default of 4m and the high-point of 20m.

Which means I should be able to go down below 20m, yes?

However, in trying, I can't get below -20m...and evening flattening the sim, I'm having trouble hitting -25m.

I'm on an Openspace sim...so does another know of an additional limitation on terraforming below waterlevel either on O/space sims or in general?

No. You can't go to negative values, at all, in any sim, no matter what the terraform limits. Normal sims and OpenSpaces are exactly the same in this regards. Terrain height is a value between zero and 255 Meters, with a possible height multiplier of as much as 2X, yielding a max possible terrain height of 255 Meters. No matter what terraform limits you have, no terrain value can exceed those limits.

If you had set the current terrain height to 120 Meters, and the water height to 100 Meters, you could terraform to 100 M below the water's surface. But you'll have a heck of a discontinuity at the edges of your sim!

The water surface in most sims is at 20 M above the absolute lowest point that you can terraform to. So if you want to form trenches or sea caves, you only have that 20M of vertical space to work in. You may want to make the "sea bottom" at 10 M, and then you have the area between 10 M and zero in which to make trenches and other sea floor features.

The terraform limits are point for point from the current terrain surface, not from some mean or average of the terrain height. The grid of height coordinates is a 256 x 256 pixel array, with each pixel representing a 1 meter square of land. So if in one part of the sim you had a 40 M plateau, and you had a +/- 10 M terraform limit, that part of the sim could be terraformed to anything from 30 to 50 M in height. Meanwhile, the beach below that cliff, at 21 meters, could be terraformed from 31m to as low as 11 M (9 M below the default water height). So in this example, you could bring the 21 M beach and the 40 M plateau to a matching height between 30 and 31 meters. But not be able to match them up at the same height any higher or lower, because one or the other would be at its limit for that point in the parcel.

Now assume in the above example that you own the sim, as a private island or OpenSpaces sim. Actually own it, and are not renting it from someone else. Now you re-bake the terrain after getting that beach and plateau both to 30 M in height. Re-baking the terrain saves the current state of the sim terraforming as the NEW baseline for terraform limits. That 30 M high area could at this point be terraformed again, anywhere in a range of 20 to 40 Meters. If you are renting the sim, and it isn't Mainland, the sim owner may be willing to do a re-bake for you, or to temporarily set higher terraform limits so you can adjust further than normally allowed.

On the mainland, the baseline will always be the terrain as the Linden's created it. They never re-bake and never change the terraform limits for residents.

Question answered.

Was aware of the ability to raise/lower mean sea level, but the discontinuity is too much of an eyesore.

Oh well, another idea ends up in the waste basket....!

Many thanks for the feedback