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Ghost navmeshes in cells 19,-9 and 20,-9


Sclerocephalus

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This is another fairly strange discovery, made again while working on my mod. Cell 19,-9 was the perfect location to place some objects, so I arranged everything, then adjusted the navmesh, finalized it without problems, saved, and got the well-known annoying editor warning on reload. Nothing too unusual, actually, but read on.

 

Inspection of my mod in TES5Edit revealed, that I did not accidentally delete a navmesh, but only modified it, as expected. There was however another navmesh in the cell, and this was marked as deleted.

 

Back in the CK with only Skyrim loaded, the cell view window listed in fact two navmeshes for this cell, FA18B and FA18E, with 122 and 432 triangles, respectively. Actually, there's only one navmesh, however: the cell has one comprehensive mesh and there's no trace to be seen of a second mesh anywhere. I did check every single triangle and they were all displayed as belonging to FA18B. When I right click on the navmesh entry for FA18E in the cell view window and select "view" (while in "navmesh only" view mode in the navmesh editor), I only get a blank screen, while doing the same for FA18B displays the cell's navmesh as expected. After modifying the navmesh to some extent, only FA18B is marked as modified in the cell view window, while FA18E is still marked as untouched. Though, when I save my mod, the CK repeatably marks FA18E as deleted.

 

A close inspection of FA18E in TES5Edit showed that this mesh, although apparently not existing, has connections to both the visible (i.e. editor-visible) navmesh and another "ghost mesh" (checked this in the CK) in cell 20,-9. So far, it also appears that these are the only two cells with ghost navmeshes in the whole southwestern Eastmarch area. What a lucky guy I am to hit just one of these two cells ...

 

On my way to solve the problem, I opened the mod in TES5Edit, removed the deletion override of FA18E and saved. Back in the CK, I suddenly had FA18E as a VISIBLE duplicate of the unmodified FA18B (sic!) overlapping with my modified navmesh in the whole of the cell. I will now reduced the duplicate to a few triangles, move it out of the way and see whether this works.

 

Now, there also is a reason why I'm posting this in the UOP forum:

(1) The navmesh in one corner of cell 19,-9 is poorly constructed and two points are below a tree with refID 000B57E7.

(2) There also remains the question whether those ghost meshes might break things and need to be taken care of.

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Not sure precisely what you did, but I just popped this cell up in a test plugin. The CK clearly shows two distinct navmeshes here. The larger bulk being up on top of the mountain, while the smaller bit is basically following the trail.

 

I ran the cover edge routine, then finalized it. Saved the results. TES5Edit shows no deleted portions, no phantom connections. There are no sudden duplicates when loaded back into the CK.

 

What I think happened is that during the course of editing the cell, you caused the two distinct navmeshes to merge into one single navmesh. The symptoms you describe are exactly the kind of thing that would result from that. One navmesh looking perfectly fine, the other showing up as deleted, and then when the deletion is reversed, showing up in the CK as an exact clone of the one you were editing.

 

The greater navmesh bug has in fact been fixed - AI not being able to path a navmesh made in an ESP. They however did NOT address the one you're seeing where merging two into one deletes one and then causes all manner of problems because it's nearly impossible to fix.

 

Best you could do is what you're planning - trim the smaller one down to a nub, then take the last remaining triangle in it and shove it underground. Edit the larger navmesh and grow it as needed. When trimming the smaller one, be extra special careful NOT to cause it to split in half or you'll end up with exactly the same problem again.

 

The navmesh next to the tree you listed is also of no concern, it wraps the tree nicely.

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After a number of tests with more or less frustrating results, I can explain what happened: You don't have to go so far to split a navmesh - just add a new point somewhere and wham ... the CK will merge all meshes into one and delete any additional navmesh records for the respective cell. If you select two points and add a new one, so as to create a triangle to connect the new point to an existing mesh from the beginning, everything works fine. If you do it the other way, by adding a point which you want to connect later, everything is immediately messed up. Just for fun,  consider a situation where you have to navmesh a balcony, which you can't connect to existing points from the beginning; if the respective cell has more than one mesh, there will be simply no way to do it right!!!

 

EDIT: Forgot to add that merging two points in either of the meshes has exactly the same effect.

 

Considering that I had nothing but Skyrim and Update.esm loaded when I noticed that the mesh was "invisible", I probably right clicked inadvertently while the mouse pointer was still inside the render window (I only don't understand why it was still displayed in the cell view window in this moment ...).

 

As for the tree, I have to contradict you. This screenshot shows the problem:

 

http://www.afkmods.com/index.php?/gallery/image/915-treeandnavmeshc19-9/

 

Anyway, thanks for taking the time to point me in the right direction.

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I've never had a problem with adding a new chunk of navmesh to an existing cell with one or more existing parts. I've ONLY ever had trouble with accidentally (or on purpose until I realized the issue) merging together two islands into one larger navmesh. Fortunately for me I learned this lesson in a small interior in Whiterun and not across two full sized wilderness cells.

 

The USKP itself has added a few missing bits of navmesh into cells with several existing islands already. You just have to watch that you never do anything to make it think you're trying to combine them, or split an existing one in half by deleting connections in the middle. Combining islands necessarily means one has to get deleted, and deleted navmeshes are death.

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