projections.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

from __future__ import division
if __name__ == "__main__":
    exit(0)

import pyproj

projs = {
    "EPSG:4326":{
                  "proj": pyproj.Proj("+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs"),
                  "bounds": (-180.0, -90.0, 180.0, 90.0),
                },
    "EPSG:3395":{
                  "proj": pyproj.Proj("+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs"),
                  "bounds": (-180.0, -85.0840591556, 180.0, 85.0840590501),
                },
    "EPSG:3857":{
                  "proj": pyproj.Proj("+proj=merc +lon_0=0 +lat_ts=0 +x_0=0 +y_0=0 +a=6378137 +b=6378137 +units=m +no_defs"),
                  "bounds": (-180.0, -85.0511287798, 180.0, 85.0511287798),
                }
        }
proj_alias = {
               "EPSG:900913": "EPSG:3857",
               "EPSG:3785": "EPSG:3857",
              }

EPSG_4326 = "EPSG:4326"

def tile_by_bbox(bbox, zoom, srs):
    """
    Converts bbox from 4326 format to tile numbers of given zoom level, with correct wraping around 180th meridian
    """
    a1, a2 = tile_by_coords(bbox[0], bbox[1], zoom, srs)
    b1, b2 = tile_by_coords(bbox[2], bbox[3], zoom, srs)
    if b1 < a1:
        b1 += 2 ** (zoom - 1)
    return a1, a2, b1, b2

def bbox_by_tile(z, x, y, srs):
    """
    Tile numbers of given zoom level to EPSG:4326 bbox of srs-projected tile
    """
    a1, a2 = coords_by_tile(z, x, y, srs)
    b1, b2 = coords_by_tile(z, x + 1, y + 1, srs)
    return a1, b2, b1, a2

def coords_by_tile(z, x, y, srs):
    """
    Converts (z,x,y) to coordinates of corner of srs-projected tile
    """
    z -= 1
    normalized_tile = (x * 1.0 / (2. ** z), 1. - (y * 1.0 / (2. ** z)))
    projected_bounds = from4326(projs[proj_alias.get(srs, srs)]["bounds"], srs)
    maxp = [projected_bounds[2] - projected_bounds[0], projected_bounds[3] - projected_bounds[1]]
    projected_coords = [(normalized_tile[0] * maxp[0]) + projected_bounds[0], (normalized_tile[1] * maxp[1]) + projected_bounds[1]]
    return to4326(projected_coords, srs)

def tile_by_coords(lon, lat, zoom, srs):
    """
    Converts EPSG:4326 latitude and longitude to tile number of srs-projected tile pyramid.
    lat, lon - EPSG:4326 coordinates of a point
    zoom - zoomlevel of tile number
    srs - text string, specifying projection of tile pyramid
    """
    zoom -= 1
    projected_bounds = from4326(projs[proj_alias.get(srs, srs)]["bounds"], srs)
    point = from4326((lon, lat), srs)
    point = [point[0] - projected_bounds[0], point[1] - projected_bounds[1]]                       #shifting (0,0)
    maxp = [projected_bounds[2] - projected_bounds[0], projected_bounds[3] - projected_bounds[1]]
    point = [1. * point[0] / maxp[0], 1. * point[1] / maxp[1]]                                     #normalizing
    return point[0] * (2 ** zoom), (1 - point[1]) * (2 ** zoom)

def to4326 (line, srs):
    """
    Wrapper around transform call for convenience. Transforms line from srs to EPSG:4326
    line - a list of [lat0,lon0,lat1,lon1,...] or [(lat0,lon0),(lat1,lon1),...]
    srs - text string, specifying projection
    """
    return transform(line, srs, EPSG_4326)

def from4326 (line, srs):
    """
    Wrapper around transform call for convenience. Transforms line from EPSG:4326 to srs
    line - a list of [lat0,lon0,lat1,lon1,...] or [(lat0,lon0),(lat1,lon1),...]
    srs - text string, specifying projection
    """
    return transform(line, EPSG_4326, srs)

def transform (line, srs1, srs2):
    """
    Converts a bunch of coordinates from srs1 to srs2.
    line - a list of [lat0,lon0,lat1,lon1,...] or [(lat0,lon0),(lat1,lon1),...]
    srs[1,2] - text string, specifying projection (srs1 - from, srs2 - to)
    """
    line = list(line)
    serial = False
    if (type(line[0]) is not tuple) and (type(line[0]) is not list):
        serial = True
        l1 = []
        while line:
            a = line.pop(0)
            b = line.pop(0)
            l1.append([a, b])
        line = l1
    ans = []
    for point in line:
        p = pyproj.transform(projs[proj_alias.get(srs1, srs1)]["proj"], projs[proj_alias.get(srs2, srs2)]["proj"], point[0], point[1])
        if serial:
            ans.append(p[0])
            ans.append(p[1])
        else:
            ans.append(p)
    return ans