Consider converting map data to geospatial in Redis

[oubiwann]

Sinusoidal data:

• 89 latitudinal lines for each degree between equator and pole
  • ~10,000km distance (at 510 pixles -> ~ 20 km per pixel)
  • between equator and pole, a degree every ~ 5.7 pixels (/ 510.0 89)
  • between equator and pole, every pixel spans ~10 arc minutes (/ 60 5.7)
• 12 meridians every 30 degrees (the sinusoidal map we're using is interrupted and has 12 gores)
  • around the equator, there is a degree every ~ 4.4 pixels (/ 1600.0 360)
  • this calculation needs to be done again, every time one moves up or down in the y direction, as the number of pixels with data has decreased ... thus as you move away from the equator in the y direction, the number of degrees longitude per pixel goes up
• calculating latitude and longitude degrees for every pixel
• while a pixel is square, the bounding area the pixel represents is approximated as a polygon
  • the top and bottom sides have different lengths
  • the sides are not parallel to each other, but rather are angled toward each other
  • thus the game world globe is not a sphere, but rather a polyhedron whose faces at the poles are three-sided polygons and everywhere else are four-sided parallelograms

Tiles in Redis:

• each pixel represents a tile
• each tile has a value for altitude, feature type (land, sea, ice), biome type
• each tile is represented as polygon
  • defined by three lat.lon coordinates at the poles (four, including the repeat of the first)
  • defined everywhere else by four lat,lon coordinates (five, including the repeat of the first)

Questions:

• how will tiles be used?
  • what tile am I in? (here's my lat/lon ... what tile contains that lat/lon?)
  • similarly, where is X?
  • how far away are X and Y? (GEODIST)
  • what else is around X? (GEORADIUS)
  • what tile is SW from here?
• to perform that last one ...
  • index ll and ur for all tiles?
  • GEORADIUS will be used, so maybe index the center location of each tile?
  • how to associate the coords of a tile's polygon corner coords with "a tile" in Redis?
• how will lat/lon be used?
  • should always be center of tile
  • sentient and object locations
  • distance between things
  • tracking travel distance

Notes on Redis GEO:

• Valid longitudes are from -180 to 180 degrees
• Valid latitudes are from -85.05112878 to 85.05112878 N
• Redis assumes that the Earth is a sphere; in the worst case distance errors may be as much as 0.5%

[oubiwann]

What sets of things are going to be useful/interesting to track locations?

• set of all players?
• set of all NPCs?
• set of all monsters?
• set of all animals?
• sets of animals? (i.e., members of a group: herds, flocks, schools)
• sets of business types? (e.g., asking an NPC where the nearest hospital, pub, armorer, etc. is)
• get nearby player(s), NPC(s), monsters, animals, business/building/organization
• get distance between any of these two
• get time to travel from one of these to another of these

[oubiwann]

This probably isn't going to be very helpful; I'm going to close, but we can always re-open if we want to reconsider.