Overviews disappearing after removing source rasters then reappearing when re-adding, anyone seen this?

Question

Hi everyone,
I ran into a behavior I couldn't find documented anywhere and wanted to check if anyone else has come across it.
I have a mosaic dataset with overviews generated and stored in a folder separate from the primary source rasters. Since the original orthophotos I'd loaded turned out to be incorrect and needed replacing, I used the Remove Rasters From Mosaic Dataset tool to physically remove all the primary rasters, leaving the overviews untouched in their own folder.
I expected the overviews to remain visible, at least at the scales they were built for, since they're independent physical raster files. Instead, as soon as the primary raster paths are removed, the overviews stop displaying as well. Interestingly, as soon as I add a new orthophoto back into the mosaic dataset, the overviews reappear.
Is this expected behavior related to how the mosaic dataset manages items (source + overview as a single row in the attribute table), or could it depend on something specific (overview format, ArcGIS version, mosaic dataset properties)?
Thanks in advance to anyone who's looked into this!

Mariano

MarianoDiNapoli · Answer

Hi, sharing what I found/tested in case it helps others.

I reproduced this behavior multiple times: removing all source rasters from a mosaic dataset makes the already-built overviews disappear from the display (even though they still physically exist as items). Adding back even a single raster makes the overviews visible again immediately.

The most plausible explanation, pieced together from Esri's documentation: the mosaic dataset's boundary is built by merging the footprints of the source rasters only (overviews are excluded from it), and the "Always Clip the Mosaic Dataset to its Boundary" property (set to Yes in my case) clips the display to that boundary. With zero source rasters, the boundary has nothing left to be built from, so the overviews end up outside the displayable area too. Adding a raster back triggers a boundary recalculation and everything becomes visible again.

Worth noting: this edge case (empty boundary → overviews not displayed) isn't explicitly documented anywhere by Esri, it's an analysis from three separate doc pages (boundary, overviews, mosaic dataset properties), not a direct quote. If anyone has a more precise reference or an alternative explanation, I'd be interested to compare notes.
Thanks

Mariano

JonM32 · Answer

@MarianoDiNapoli

I've had mosaic datasets display their overviews after removing the source images. Usually you get the checkerboard until zoomed out enough.

Possibly after you removed the source data, you could run this tool to get the mosaic dataset up to date: Synchronize Mosaic Dataset (Data Management Tools) | ArcGIS Pro documentation