These simple utilities extract the cm93 chart cell bounding boxes
for use with mapproxy-seed to retrieve charts from tile servers
for harbors around the world

==== Example ====

Edit mbtiles-nautical-boxes/config.yaml to select a tile server

$ mapproxy-seed -s nautical-17.yaml -f config.yaml

This program is a little buggy as it sometimes aborts, but
also tends to "complete" without completing the database.
Run it as many times as needed until it completes with 0 tiles fetched.

$ cp mbtiles-nautical-boxes/cache_data/mapproxy-seed-output.mbtiles nautical-17.mbtiles