OpenSeaMap-dev:Downloadable Raster Charts

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Reason for ChartBundler

Lets talk a bit about amounts here and not low stress or high stress.

Using the charts offline on a mobile device. Lets say the display is about 1024x1024 Pixel, then we will need at least 16 tiles per map. If we start on zoom level 8 with the bounding box and continue to zoom level 16 for the harbours, we need around 2 Mio tiles. This 16 tiles on zoom level 8 is about the northern Adria. If we want the Channel just skipping Lands End up to the belgian coast, this would be 6 by 5 on zoom level 8.

Status Quo

prefabricated charts

  • pros:
    • low stress on tile servers
  • cons:
    • set up needed
    • needs to be maintained
    • not always up to date
    • might not fit users needs


on demand

  • pros:
    • up to date
    • fits individual needs
  • cons:
    • high stress on tile servers
    • users have to do some research, might be a complex task



cache & proxy tile server

  • TileStache provides
    • numerous caches (eg. disk, Memcache, Amazon S3, MBTiles)
    • TMS and WMS proxy
    • fast and faster using nginx
    • cache max-age: 30 days?


  • served by cache & proxy tile server at minimum cost
    • tiles in TMS z/x/y directory structure
    • tiles in TMS z/x/y structure encapsulated in sqlite file ( mbtiles )
    • tiles in ??? structure encapsulated in sqlite file (OruxMaps)
    • tiles in ??? structure encapsulated in sqlite file (Locus)
    • single raster file stiched together via script and imagemagic

bounding boxes/ tile sets

  • coastal / ocean / open waters
  • inland waterways
  • lakes
    • ...

web frontend

  • map showing boundingboxes according zoom level transas sample
  • sortable table
  • search by name/number/area/purpose
  • functions:
    • search prefabricated files, check age
    • trigger generating script in case file does not exist/ is obsolete