map_project

This gem provides a set of tools which can help users to map geo lat-lng to viewport coords. For example, you can use this gem to convert lat-long points to html <div> coords.

This gem applies to many user cases, for example, when:

• You have a set of lat,long positions, and want to drop them as pins on map
• You have a map, and want to sprite it in to multiple viewports
• You need the actual on-map boundary
• You need mapping between lat,long and google world, google pixel coords.
• ...

Install

In Gemfile:

gem 'map_project'

and bundle:

$ bundle install

Then, include:

include MapProject

In any files you need.

Usage:

If you have a boundary:

{sw: [MIN_LAT, MIN_LNG],
 ne: [MAX_LAT, MAX_LNG]})

and you know your viewport sizes (ex. width and height of a <div>), you can get the zoom level:

zoom_level = get_bounds_zoom_level(boundary, viewport_width, viewport_height)

Once you get the zoom level, you can do a lot of more:
First, create a map_project object:

map_projection = MapProject.new({zoom_level: ZOOMLEVEL, lat: LAT, long: LONG, viewport_w: VIEWPORT_WIDTH, viewport_h: VIEWPORT_HEIGHT})

The :lat and :long are the geo position of the center. Example:

map_projection = MapProject.new({zoom_level: 15, lat: 37.294742, long: -122.019252, viewport_w: 1024, viewport_h: 1024})

Then, you can:
Convert geo lat-lng to Google World Coords:

map_projection.world_coords

Convert geo lat-lng to Google Pixel Coords:

map_projection.pixel_coords

Get number of pixels per latitude/longitude inside this map area:

map_projection.pixel_per_lat
map_projection.pixel_per_long

Map any geo lat-lng points to viewport coords:

(0,0)         (0, x)
     ------------
     |          |
     | viewport |
     |          |
     ------------
(y, 0)        (x, y)
map_project.offset_on_viewport(input_lat, input_long)

Get pixel boundary on this viewport:

map_projection.pixel_bounds_based_on_center

The input boundary you used for getting zoom level may be different from the real boundary on map. Get actual geo boundary on this viewport:

map_projection.geo_bounds_based_on_center