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Given a set of tiles covering a large area at a particular zoom level (These are online on someone's tile server and will need scraping, but let's assume these are on disk if it's easier. With TMS google style filenames)

...what is the easiest way to generate, by straightforward scaling down, a pyramid of tiles for lower zoom levels? No need for reprojecting just 1/2 scaling.

I could write my own script to do this. Just stitch together four tiles and scale down the resulting image by half, to give you a single tile at the next zoom level. And repeat. It's almost easy enough for me to go ahead an do this, but I'm guessing it's been done before! What are the best existing tools and established approaches for doing this? It looks like I could use gdal2tiles given a single image file. I could create such a file by tile stitching e.g. with BigMap, but is there a tool (or params) which lets me skip that step?

Just to pique your interest in the question, let me tell you the fun thing I'm actually thinking of doing: The TIGER Edited Map is a really neat tool for OpenStreetMap contributors in the U.S., letting them see areas where the data has never been edited since the TIGER import (areas where more contributors are needed) but it's only generated by MapQuest from zoom level 8 and above.

TIGER edited map at the lowest zoom generated zoom level 8

It would be great (and quite easy hopefully) to generate a more zoomed out overview at zooms 7,6,5,4. We'll be scaling the text of place names too which is a shame, but not really a big worry.

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Would you be interested in Python Solution? TileCloud pypi.python.org/pypi/tilecloud/0.1 (uses Python's Multi processing Library - docs.python.org/library/multiprocessing.html) –  Mapperz Aug 30 '12 at 16:09
    
I am very much interested in python solutions, anything I could run on a server yes (although the QGIS suggestion is also helpful) –  Harry Wood Sep 7 '12 at 1:03
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2 Answers 2

QGIS has a built in function for creating raster pyramids. When resampling you can choose average or nearest neighbor methods.

Once you have QGIS, import the raster, then right-click on it in the Layers panel on the left of the screen, and select Properties. In this dialog choose the Pyramids tab. Further documentation on how to use this function is here.

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Just came across "TileTool" which seems to do be largely dedicated to this task

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