there seams to be a over laping of the tex when using .ctx
hear is an example
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this is a level1 at 1024x1024 tile of the amamizon delta
the next image is a1024x1025 pixel tile (tx_1_1.png) then rescaled to 1024x1024 - the extra pix. is at the equater
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see the diff. the line is almost gone
the two tiles are tx_1_0 and tx_1_1 for level 1