OpenSeaMap-dev:Downloadable Raster Charts

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.

• see Discussion

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

Links:

• OpenNauticalCharts (outdated)
• Chart-Bundler (work in progress)

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

Links:

• Chart-Designer (work in progress)
• OSM-Wiki
• smrender-online
• MOBAC (banned by most tile-servers due to unreasonable load)
• GMapCatcher

Ideas

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?

formats

• served by cache & proxy tile server at minimum cost
  • tiles in TMS z/x/y directory structure (eg. gps-32, openlayers)
  • tiles in TMS z/x/y structure encapsulated in sqlite file ( mbtiles, eg. tilestache )
  • 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 (eg. .kap/openCPN)
  • gemf format - compact format for tiles, can be read by various libraries - e.g. osmdroid, simple to handle gemf format

bounding boxes/ tile sets

• coastal / ocean / open waters
  • stick to well known INT-charts
• inland waterways
  • generate corridor (x-tiles wide) along centerline of waterway GMapCatcher example
• 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  • trigger generating script in case file does not exist/ is obsolete