MATLAB: Drawing Contours on globe/world map

contourMapping Toolbox

I have designed a software for computing relative antenna gain of satellite coverage/foot prints. The software takes latitude, longitude and gain as inputs and interpolates relative antenna gain in between the contours and generates contour plots. Pls tell me how can i display these contour plots on the globe according to the input latitude and longitude.

Regards Somayyah Jurair

Best Answer

Hi,

I'd make use of the m_map toolbox for this. Rather than give you exact code, (read: I cant remember offhand) let me rather explain loosely how to go about it.

First get the toolbox http://www.eos.ubc.ca/~rich/map.html or do a Google search on "m_map" Then make a plot of whatever section of the world you're interested in.

Next, transform your longitude and latitude to coordinates on the plot.

Finally overlay a contour or contourf plot of your data on the figure.

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Pietro - if you know the country code for the city, then you could try the following function which makes use of the Yahoo GeoPlanet Web Service, GeoPlanet YQL Tables.

 % Uses YQL to query the geo.places database for the latitude and longitude
 % of a city, given the city name and country code.
 function [latDegs, lonDegs] = getLatLonViaYql(city,countryCode)
    % build the YQL query
    yqlQuery = sprintf(['select centroid.latitude,centroid.longitude ' ...
                        'from geo.places '                             ...
                        'where text="%s" and country.code="%s" and '   ...
                        'placeTypeName.code="7"'],                     ...
                        city, countryCode);
    % build the URL
    yqlUrl = ['http://query.yahooapis.com/v1/public/yql?q=' yqlQuery];
    % replace blank spaces with %20
    yqlUrl = strrep(yqlUrl,' ','%20');
    % retrieve the data
    xmlData = urlread(yqlUrl);
    % get the latitude and longitude (here we assume that the latitude is
    % within <latitude>XYZ</latitude> and the longitude within
    % <longitude>UVW</longitude> tags)
    posData = regexp(xmlData,'>[0-9.-]+<','match');
    % if exactly two tags match the above regexp then parse the latitude
    % and longitude data
    if length(posData)==2
        latDegs = str2double(char(posData{1}(2:end-1)));
        lonDegs = str2double(char(posData{2}(2:end-1)));
    else
        latDegs = 0;
        lonDegs = 0;
    end
 end

The latitude and longitude positions can then be obtained as

 [latLondon,lonLondon] = getLatLonViaYql('London','GB')
 latLondon =
                 51.507702
 lonLondon =
                  -0.12797
 [latRome,lonRome] = getLatLonViaYql('Rome','IT')
 latRome =
                 41.898399
 lonRome =
                   12.4956

In the YQL query, we grab the "centroid latitude and longitude of a "bounding box" that surrounds the city. (This box is defined by south-west and north-east positions.) Whether this is accurate enough for your application remains to be seen. But constructing two vectors as

 lat = [latLondon ; latRome];
 lon = [lonLondon ; lonRome];

and executing

 plot(lon,lat,'.r','MarkerSize',20)
 plot_google_map

puts the red markers at the positions of London and Rome on the map.

EDIT

Updated the above code to include an additional where condition/clause to ensure that the record returned corresponds to a "Town". Pietro observed that at least two records were being returned for cities like Oslo, Berlin, and Sofia.

Best Answer

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