Compatible resolutions for LTIMosaicFilter

[Tubaman]

I have 3 .sid images for which I'm attempting to use a mosaicFilter to create a composite image. If I pass 'false' to the useMultires parameter of initialize() or checkResolutionConformance(), I get an 'incompatible X resolutions' error (50206).

According to the IMAGE:X_RESOLUTION metadata tag, the resolution of all 3 images is 0.000008 (i.e. 80cm). However, if I do a getGeoCoord() on the 3 readers, the resolutions returned are 0.0000077408, 0.0000077454 and 0.0000077496, which looks like it could be the reason for the incompatible resolutions message.

I don't currently understand why the actual resolution values are different from the tagged values (something to do with the projection with the image tiles being at slighly different lat/lon maybe? Each tile covers an area of approx 0.2 degrees square). My question though is what is the likely performance penalty if I set the useMultires parameter to true so that the images can be resampled? This sounds expensive, and if so is it possible to get the mosaicFilter to ignore the tiny difference and force it to create the mosaic without resampling?

Many thanks in advance for any help!