/
plot_openstreetmap.m
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plot_openstreetmap.m
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function hgrp = plot_openstreetmap(varargin)
% PLOT_OPENSTREETMAP Plots OpenStreetMap on the background of a figure.
% h = PLOT_OPENSTREETMAP(Property, Value,...)
%
% Properties:
%
% 'Alpha' Transparency level of the map (0 is fully transparent, 1
% is opaque). Default: 1.
% 'BaseUrl' URL for the tiles (Default:
% 'http://a.tile.openstreetmap.org'). More tile URLs:
% https://wiki.openstreetmap.org/wiki/Tiles#Servers
% 'Scale' Resolution scale factor (Default: 1). Using Scale=2 will
% double the resulotion of the map image and will result in
% finer rendering.
% 'MaxZoomLevel' Maximum tile zoom level (Default: 16). This sets the
% maximum zoom level that will be requested from the tile
% server. Note that not all tile servers will support
% high zoom levels.
%
% EXAMPLE
%
% x = [11.6639 11.7078 11.7754 11.8063 11.8797];
% y = [57.6078 57.6473 57.6607 57.6804 57.6886];
% figure('Color', 'w'); plot(x, y, 'o-', 'LineWidth', 2);
% hBase = plot_openstreetmap('Alpha', 0.4, 'Scale', 2)
% hSea = plot_openstreetmap('Alpha', 0.5, 'Scale', 2, 'BaseUrl', "http://tiles.openseamap.org/seamark")
% title('Map data from OpenStreetMap and OpenSeaMap');
%
p = inputParser;
validScalar0to1 = @(x) isnumeric(x) && isscalar(x) && (x >= 0) && (x <=1);
validScalarPos = @(x) isnumeric(x) && isscalar(x);
validMaxZoomLevel = @(x) isnumeric(x) && isscalar(x) && (x >= 0);
addParameter(p, 'BaseUrl','http://a.tile.openstreetmap.org', @isstring);
addParameter(p, 'Alpha', 1, validScalar0to1);
addParameter(p, 'Scale', 1, validScalarPos);
addParameter(p, 'MaxZoomLevel', 16, validMaxZoomLevel);
parse(p,varargin{:});
ax = gca();
curAxis = axis(ax);
verbose = false;
baseurl = p.Results.BaseUrl;
alpha = p.Results.Alpha;
scale = p.Results.Scale;
maxZoomLevel = p.Results.MaxZoomLevel;
%% Convertion from lat lon to tile x and y, and back.
% See: https://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
% Example tile x=272, y=154: https://a.tile.openstreetmap.org/9/272/154.png
lon2x = @(lon, zoomlevel) floor((lon + 180) / 360 * 2 .^ zoomlevel);
lat2y = @(lat, zoomlevel) floor((1 - log(tan(deg2rad(lat)) + (1 ./ cos(deg2rad(lat)))) / pi) / 2 .* 2 .^ zoomlevel);
x2lon = @(x, zoomlevel) x ./ 2.^zoomlevel * 360 - 180;
y2lat = @(y, zoomlevel) atan(sinh(pi * (1 - 2 * y ./ (2.^zoomlevel)))) * 180 / pi;
%%
oldHold = ishold();
hold on;
%% Adjust aspect ratio.
adjust_axis(ax, curAxis);
ax.PlotBoxAspectRatioMode = 'manual';
%% Compute zoom level.
[width, height] = ax_width_pixels(ax);
width = width * scale;
height = height * scale;
zoomlevel = get_zoomlevel(curAxis, width, height, maxZoomLevel);
%% Memoize downloaded tiles, to save bandwidth.
memoizedImread = memoize(@imread);
memoizedImread.CacheSize = 200;
%% Get tiles and display them.
minmaxX = lon2x(curAxis(1:2), zoomlevel);
minmaxY = lat2y(curAxis(3:4), zoomlevel);
hgrp = hggroup;
for x = min(minmaxX):max(minmaxX)
for y = min(minmaxY):max(minmaxY)
url = sprintf("%s/%d/%d/%d.png", baseurl, zoomlevel, x, y);
if verbose
disp(url)
end
[indices, cmap, imAlpha] = memoizedImread(url);
% Some files, t.ex. from openseamap with transparency, come without
% colormap. They have three dimensions in indices already.
if size(indices, 3) > 1
imagedata = indices;
else
imagedata = ind2rgb(indices, cmap);
end
if numel(imAlpha) == 0
imAlpha = 1;
end
im = image(ax, ...
x2lon([x, x+1], zoomlevel), ...
y2lat([y, y+1], zoomlevel), ...
imagedata, ...
'AlphaData', alpha*imAlpha...
);
set(im,'tag','osm_map_tile')
set(im,'Parent',hgrp)
uistack(im, 'bottom') % move map to bottom (so it doesn't hide previously drawn annotations)
end
end
set(hgrp,'tag','osm_map')
%%
function [width, height] = ax_width_pixels(axHandle)
orig_units = get(axHandle,'Units');
set(axHandle,'Units','Pixels')
ax_position = get(axHandle,'position');
set(axHandle,'Units',orig_units)
width = ax_position(3);
height = ax_position(4);
end
function adjust_axis(axHandle, curAxis)
% adjust current axis limit to avoid strectched maps
[xExtent,yExtent] = latLonToMeters(curAxis(3:4), curAxis(1:2) );
xExtent = diff(xExtent); % just the size of the span
yExtent = diff(yExtent);
% get axes aspect ratio
drawnow
orig_units = get(axHandle,'Units');
set(axHandle,'Units','Pixels')
ax_position = get(axHandle,'position');
set(axHandle,'Units',orig_units)
aspect_ratio = ax_position(4) / ax_position(3);
if xExtent*aspect_ratio > yExtent
centerX = mean(curAxis(1:2));
centerY = mean(curAxis(3:4));
spanX = (curAxis(2)-curAxis(1))/2;
spanY = (curAxis(4)-curAxis(3))/2;
% enlarge the Y extent
spanY = spanY*xExtent*aspect_ratio/yExtent; % new span
if spanY > 85
spanX = spanX * 85 / spanY;
spanY = spanY * 85 / spanY;
end
curAxis(1) = centerX-spanX;
curAxis(2) = centerX+spanX;
curAxis(3) = centerY-spanY;
curAxis(4) = centerY+spanY;
elseif yExtent > xExtent*aspect_ratio
centerX = mean(curAxis(1:2));
centerY = mean(curAxis(3:4));
spanX = (curAxis(2)-curAxis(1))/2;
spanY = (curAxis(4)-curAxis(3))/2;
% enlarge the X extent
spanX = spanX*yExtent/(xExtent*aspect_ratio); % new span
if spanX > 180
spanY = spanY * 180 / spanX;
spanX = spanX * 180 / spanX;
end
curAxis(1) = centerX-spanX;
curAxis(2) = centerX+spanX;
curAxis(3) = centerY-spanY;
curAxis(4) = centerY+spanY;
end
% Enforce Latitude constraints of EPSG:900913
if curAxis(3) < -85
curAxis(3:4) = curAxis(3:4) + (-85 - curAxis(3));
end
if curAxis(4) > 85
curAxis(3:4) = curAxis(3:4) + (85 - curAxis(4));
end
axis(axHandle, curAxis); % update axis as quickly as possible, before downloading new image
drawnow
end
function zoomlevel = get_zoomlevel(curAxis, width, height, maxZoomLevel)
[xExtent,yExtent] = latLonToMeters(curAxis(3:4), curAxis(1:2) );
minResX = diff(xExtent) / width;
minResY = diff(yExtent) / height;
minRes = max([minResX minResY]);
tileSize = 256;
initialResolution = 2 * pi * 6378137 / tileSize; % 156543.03392804062 for tileSize 256 pixels
zoomlevel = floor(log2(initialResolution/minRes));
% Enforce valid zoom levels: 1 <= zoom <= maxZoomLevel (Default: 16)
zoomlevel = min(max(zoomlevel, 1), maxZoomLevel);
end
function [x,y] = latLonToMeters(lat, lon )
% Converts given lat/lon in WGS84 Datum to XY in Spherical Mercator EPSG:900913"
originShift = 2 * pi * 6378137 / 2.0; % 20037508.342789244
x = lon * originShift / 180;
y = log(tan((90 + lat) * pi / 360 )) / (pi / 180);
y = y * originShift / 180;
end
end