Max Height Data
The MHDT Field
Max Height Data (MHDT) is a possible value that can be set in CELL and WRLD (Worldspace) records. It may vary between plugins if it is not missing entirely and causes conflicts that have no obvious solution.
In many Skyrim.esm records the field is left empty while the DLC add a value:
Certain mods in turn forward one of the values from the official master files, add their own, or leave the field empty again. How should these conflicts be addressed?
What does MHDT do?
The following is a quote from Arthmoor (source):
This MHDT data is speculated to have something to do with dragon height data. Telling them where they can and can’t fly while airborn. Sort of serving as their navmesh. There is no solid proof of this though.
[…]
With thousands of mods in the game not forwarding this data (because why would they - it requires DLC) there is no way that [max height data] being missing is going to matter. Every mod would break the game. Bethesda’s own DLC would break the game, because Dragonborn’s MHDT data will clearly not be taking Dawnguard into account, and vice-versa. So just the mere presence of Dragonborn in the game should cause Castle Volkihar to get blocked.
On the xEdit Discord, Arthmoor added (source):
TechAngel wrote the following in a post in the STEP forum (source):
MHDT Conflicts
As TechAngel mentioned, Occlusion generated with xLODGen or DynDOLOD as well as the DynDOLOD plugins themselves often modify Max Height Data for cells. These outputs will overwrite everything else.
Where DynDOLOD and xLODGen do not recalculate Max Height Data, I recommend forwarding the value from the Unofficial Skyrim Special Edition Patch.
Recalculating MHDT
If Max Height Data does not match placed objects, dragons may clip through tall trees or buildings in flight. You should be able to fix this by loading the plugin adding the tall objects into the Creation Kit and regenerating Max Height Data. Make sure it then overwrites any other plugins modifying the same CELL.
