[udig-devel] Large GeoTiff not rendering at high zoom

[Ned Haubein <bluehen597@xxxxxxxxx>]

Hi,

After working for a while to get a large GeoTiff file (2.7GB, 51511x67140 pixels) into uDig 1.2, I thought I'd share my approach for new users and ask a question of the more experienced.

Just dragging that large of a file into uDig didn't work - the layer would show up in the layers list and an entry in the Catalog, but nothing rendered.  It would show progress for a while and then silently stop.  The only error I saw was when entering the layer properties.  The histogram building failed due to width*height>Integer.MAX.

After some searching, I was successful in using GDAL to add overviews to the tiff file:

gdaladdo -r average filename.tif 2 4 8 16

I got a few warnings about "computing overviews on raster palette index", but the output images seemed to look ok for the most part.

When dragging the new tiff into uDig it renders fine and is actually pretty snappy in its rendering.

Now to my question:  When I zoom in too far (past 1:2921 scale), the raster layer just disappears.  Other layers are drawn fine, and if I zoom out the raster from the geotiff renders ok again.  There are no log or console errors.  Any ideas what is going on?  Am I basically just seeing the same initial problem of not being able to render the base level of the image b/c I have zoomed in past the "overview 2" level?  Has anyone seen this?  Are there workarounds?

I did build a pyramid using gdal_retile.  I could import a mosaic directory into udig for the lower resolution levels, but only the level imported was visible - no transitions up and down the pyramid when zooming, so I think gdaladdo was the right choice.

Any thoughts or suggestions welcome.

Thanks to the developers,

- Ned