source: src/django_gheat/wlheatmap/tile.py

#!/usr/bin/env python
#
# Hack to show image generation realtime, sample tile server implementation.
#
# Rick van der Zwet <info@rickvanderzwet.nl>
from collections import defaultdict
from django.core.management import setup_environ
from django.db.models import Max
from django.http import HttpResponse
from django.views.decorators.cache import cache_page
from gheat.models import *
import os
import pygame
import sys
import tempfile
import time


class PyGamePicture():
  """ Basic PyGame class, allowing simple image manipulations """
  def __init__(self, method, size):
    self.surf = pygame.Surface(size,flags=pygame.SRCALPHA)

  def center_crop(self,size):
    """ Resize to make centered rectange from image """
    new_surf = pygame.Surface(size, flags=pygame.SRCALPHA)
    curr_size = self.surf.get_size()
    new_surf.blit(self.surf,(0,0),
      ((curr_size[0] - size[0]) / 2, (curr_size[1] - size[1]) / 2, size[0], size[1]))
    self.surf = new_surf

  def save_and_get_image(self,filename):
    """ Save the file to the location and return the file """
    basedir = os.path.dirname(filename)
    if not os.path.isdir(basedir):
      os.makedirs(basedir)
    pygame.image.save(self.surf,filename)
    return open(filename,'r').read()

  def get_image(self,format='png'):
    f = tempfile.NamedTemporaryFile(suffix=format)
    pygame.image.save(self.surf,f.name)
    f.seek(0)
    return f.read()



  def add_circle(self, center, radius, colour=(255,0,0), transparancy=0):
    """ 
    Hack to add lineair gradient circles and merge with the parent. The
    transparancy can be configured to make the circles to fade out in the
    beginning
    """
    # Make calculations and ranges a whole bunch more easy
    radius = int(math.ceil(radius))

    new_surf = pygame.Surface(self.surf.get_size(),flags=pygame.SRCALPHA)
    alpha_per_radius = float(2.55 * (100 - transparancy)) / radius
    for r in range(radius,1,-1):
      alpha = min(255,int((radius - r) * alpha_per_radius))
      combined_colour = colour + (alpha,)
      pygame.draw.circle(new_surf,combined_colour,center,r,0)
    self.surf.blit(new_surf,(0,0),special_flags=pygame.BLEND_RGBA_MAX)


class LatLonDeg():
  """ Helper class for coordinate conversions """
  def __init__(self,lat_deg, lon_deg):
    self.lat = lat_deg
    self.lon = lon_deg
  def __str__(self):
    return "%.5f,%.5f" % (self.lat, self.lon)

  def deg_per_pixel(self,other,pixel_max):
    return(LatLonDeg(abs(self.lat - other.lat) / pixel_max, abs(self.lon - other.lon) / pixel_max))



# Convertions of tile XYZ to WSG coordinates stolen from:
#    http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
# <stolen>
import math
def deg2num(lat_deg, lon_deg, zoom):
  lat_rad = math.radians(lat_deg)
  n = 2.0 ** zoom
  xtile = int((lon_deg + 180.0) / 360.0 * n)
  ytile = int((1.0 - math.log(math.tan(lat_rad) + (1 / math.cos(lat_rad))) / math.pi) / 2.0 * n)
  return(xtile, ytile)

def num2deg(xtile, ytile, zoom):
  n = 2.0 ** zoom
  lon_deg = xtile / n * 360.0 - 180.0
  lat_rad = math.atan(math.sinh(math.pi * (1 - 2 * ytile / n)))
  lat_deg = math.degrees(lat_rad)
  return(LatLonDeg(lat_deg,lon_deg))
# </stolen>


def boundbox_deg(x,y,z):
  """ Calculate the boundingbox for a image """
  return (num2deg(x,y,z), num2deg(x+1,y+1,z))



def make_tile(x,y,z,filter={},colour=(255,0,0)):
  """
  Crude attempt to generate tiles, by placing a gradient circle on a
  coordinate point.  Generate a larger tile  and make sure to plot related
  points first and then crop it to the required size (250x250).
  
  Many stuff NOT implemented yet, like:
  - Caching Images.
  - Conditional Filtering of Meting to allow display of sub-results.
  - Defining a extra level of transparency if you like to layer multiple tiles
    on top of each-other.
  - Color variation, allow the user to dynamically choose a the colour the
    points to be.
  - Advanced data plotting, like trying to guess the remainder points.
  """
  
  SIZE = 250
  
  nw_deg,se_deg = boundbox_deg(x,y,z)

  
  Picture = PyGamePicture
  resolution_deg = nw_deg.deg_per_pixel(se_deg, SIZE)
  # Converting LatLon to Meters is discussed here:
  #  http://stackoverflow.com/questions/3024404/transform-longitude-latitude-into-meters
  tile_height = float(40008000) / (2 ** z)
  meters_per_pixel = float(tile_height) / SIZE
  
  # Worst case scenario could a circle with 100% 'outside' our 250x250 range
  # also add data to the picture as circles are used
  border_pixels = 100 / meters_per_pixel / 2

  im = Picture("RGBA", (SIZE + border_pixels * 2,) * 2)

  nw_deg.lat += resolution_deg.lat * border_pixels
  nw_deg.lon -= resolution_deg.lon * border_pixels
  se_deg.lat -= resolution_deg.lat * border_pixels
  se_deg.lon += resolution_deg.lon * border_pixels
  
  lat_min = 999
  lon_min = 999
  lat_max = 0
  lon_max = 0

  for key in filter.keys():
    if filter[key] == 'all':
      del filter[key]

  filter.update({
    'latitude__lte' : nw_deg.lat,
    'latitude__gte' : se_deg.lat,
    'longitude__lte' : se_deg.lon,
    'longitude__gte' : nw_deg.lon
  })
  # Limit such that high level zooms does not get the whole database
  metingen = Meting.objects.filter(**filter).order_by('?')[:1000].values_list('latitude', 'longitude', 'signaal')

  # Round numbers example to a less fine grain measurements
  # d = defaultdict(list)
  # for lat,lon, signaal in metingen:
  #   d[(round(lat,5),round(lon,5))].append(signaal)

  # metingen = []
  # for (lat,lon),signals in d.iteritems():
  #   metingen.append((lat,lon,max(signals)))

  # XXX: Signal is not normalized in the database making it unknown when a
  # signal is said to be 100% or when it is actually less, currently seems to
  # copy the raw reported values
  MAX_SIGNAL = 50
  # XXX: The radius relates to the zoom-level we are in, and should represent
  # a fixed distance, given the scale. Assume signal/distance to be lineair
  # such that signal 100% = 100m and 1% = 1m.
  # 
  # XXX: The relation is not lineair but from a more logeritmic scape, as we
  # are dealing with radio signals
  #
  MAX_RANGE = 100
  
  def dif(x,y):
    """ Return difference between two points """
    return max(x,y) - min(x,y)
  
  for (latitude, longitude, signaal) in metingen:
    lat_min = min(lat_min, latitude)
    lat_max = max(lat_max, latitude)
    lon_min = min(lon_min, longitude)
    lon_max = max(lon_max, longitude)
    xcoord = int(dif(nw_deg.lon,longitude) / (resolution_deg.lon))
    ycoord = int(dif(nw_deg.lat,latitude) / (resolution_deg.lat))

    # TODO: Please note that this 'logic' technically does apply to WiFi signals,
    # if you are plotting from the 'source'. When plotting 'measurement' data you
    # get different patterns and properly need to start looking at techniques like:
    # Multilateration,Triangulation or Trilateration to recieve 'source' points.
    # 
    # Also you can treat all points as seperate and use techniques like
    # Multivariate interpolation to make the graphs. A nice overview at:
    #     http://en.wikipedia.org/wiki/Multivariate_interpolation
    #
    # One very intersting one to look at will be Inverse distance weighting
    # with examples like this: 
    # http://stackoverflow.com/questions/3104781/inverse-distance-weighted-idw-interpolation-with-python
    signal_normalized = MAX_RANGE - (MAX_SIGNAL - signaal)
    im.add_circle((xcoord,ycoord),float(signal_normalized) / meters_per_pixel,colour, MAX_SIGNAL - signaal)
    #im.add_point((xcoord,ycoord),float(signal_normalized) / meters_per_pixel,colour, MAX_SIGNAL - meting.signaal)
  
  im.center_crop((SIZE,SIZE))
  return im

def pre_process_tile(request,zoom,x,y):
  filter = {}
  colour = (255,0,0)
  for key, value in request.GET.iteritems():
    if key == 'colour':
      colour = tuple(map(int,value.split(',')))
    else:
      filter[key] = value
  now = time.time()
  im = make_tile(int(x),int(y),int(zoom),filter=filter,colour=colour)
  return im

# Create your views here.
# N.B: This cache is handly is you are using in standalone mode
#@cache_page(60 * 60 * 24, cache="tile_cache")
def serve_tile(request,zoom,x,y):
  im = pre_process_tile(request,zoom,x,y)
  data = im.get_image('png')
  return HttpResponse(data,mimetype="image/png")

def fixed_wl_only(request,zoom,x,y): 
  """ Pre-render and save attempt """
  im = pre_process_tile(request,zoom,x,y)
  data = im.save_and_get_image('/usr/local/var/django/tile/fixed/wl-only/%s/%s,%s.png' % (zoom, x, y))
  return HttpResponse(data,mimetype="image/png")