This is separate to the related export issue that I have raised (https://feedback.secondlife.com/server-bugs/p/terrain-export-is-badly-encoded-quantised-leading-to-significant-resolution-loss).

It seems plausible that it could be related to https://feedback.secondlife.com/feature-requests/p/remove-lossy-compression-from-terrain-heightmap

Generating a precise height map that complies to the specifications defined on the LL wiki does not result in the expected results upon import. This makes it impossible to plan a proper terrain layout with any degree of confidence. Given that OpenSim correctly and accurately imports the data as per the SL specification it means that those people using a local installation of OpenSim to test and prepare regions for use in SecondLife are going to be very disappointed.

Repro steps:

1) Find a raw file for a flat terrain (e..g 20m)

I can provide example files but Canny is too frustratingly lame to accept them as attachments.

2) set water to the same level

3) note that the land is not at the same level as the water.

Secondary tests.

1) Import a linear ramp. (can be generated using my terrain tools) https://github.com/beqjanus/terrain-tools

2) Note that it is far from linear