I'm not familiar with the Oblivion editing tools, so I just jumped onto a wiki:
http://cs.elderscrolls.com/constwiki/in ... ap_EditingImport This option allows you to use 1024x1024 16-bit RAW format images as a starting template for heightmap painting. These should be located in your "Oblivion\Data\HeightField" directory and named according to this grid (ex: Oblivion\Data\HeightField\0_0.raw). The files should also have been saved with these Raw Option settings: Header: 0, Non-interleaved Order, Count: 1, Depth: 16 Bits, Byte Order: IBM PC.
So I'm assuming you need something with those specs. As a test, I generated a quick 2048 * 2048 terrain heightfield with L3DT.
File> Export> Export Active Layer (Ctrl+E), to bring up the export dialog. Make sure you check "Split Map into Tiles (mosaic map)".
The Filetype will show L3DT mosaic map. The options button will be greyed out.
Click the browse button, browse to a folder. Type a short Name, click Save. Then click Next
On PAGE 2 of the Export Wizard, we now have the setting for the individual files in the mosaic.
Make sure Tile Size is set to 10247*1024. Select RAW as file-type. Click Options.
Double check that all the settings are appropriate. (I didn't see anything I had to change to match the above specs). Click OK. Click OK again.
I generated 4 files named "filename_x0y0.raw", "filename_x0y1.raw". These have an origin of the Bottom Left corner of the map in L3DT, as explained on the wiki-page:
http://www.bundysoft.com/docs/doku.php? ... ms:mosaicsSo, you'll have to rename them to match up with the grid-system used by Oblivion.
Hope that helps!