JSONP as well as JSON for chart format "chof"

[Paul]

Hi,

I would like to programmatically create pins and markers for a chart
created using the Google Charts API. This relies on knowing the
location of the chart's data points within the chart image.

The chof=json parameter to a Google Chart will return me the JSON
required to create an image map, and therefore this data will also be
usable to position pins or markers over the chart image.


For example the URL:

http://chart.apis.google.com/chart?cht=bvg&chs=250x150&chd=s:Monkeys&chxt=x,y&chxs=0,ff0000,12,0,lt|1,0000ff,10,1,lt&chof=json

Returns the JSON:

{"chartshape":[{"name":"axis0_0","type":"RECT","coords":
[32,135,37,144]},{"name":"axis0_1","type":"RECT","coords":
[63,136,66,144]},{"name":"axis0_2","type":"RECT","coords":
[94,136,99,144]},{"name":"axis0_3","type":"RECT","coords":
[125,135,130,144]},{"name":"axis0_4","type":"RECT","coords":
[156,136,162,144]},{"name":"axis0_5","type":"RECT","coords":
[187,135,192,144]},{"name":"axis0_6","type":"RECT","coords":
[218,135,223,144]},{"name":"axis1_0","type":"RECT","coords":
[11,126,16,133]},{"name":"axis1_1","type":"RECT","coords":
[6,100,16,108]},{"name":"axis1_2","type":"RECT","coords":[6,75,16,83]},
{"name":"axis1_3","type":"RECT","coords":[6,50,16,57]},
{"name":"axis1_4","type":"RECT","coords":[6,25,16,32]},
{"name":"axis1_5","type":"RECT","coords":[0,0,15,7]},
{"name":"bar0_0","type":"RECT","coords":[24,129,47,104]},
{"name":"bar0_1","type":"RECT","coords":[55,129,78,46]},
{"name":"bar0_2","type":"RECT","coords":[86,129,109,48]},
{"name":"bar0_3","type":"RECT","coords":[117,129,140,55]},
{"name":"bar0_4","type":"RECT","coords":[148,129,171,67]},
{"name":"bar0_5","type":"RECT","coords":[179,129,202,26]},
{"name":"bar0_6","type":"RECT","coords":[210,129,233,38]}]}


I have two problems. One, I cannot use XMLHTTPRequest to get the JSON
as cross-domain requests are not allowed. I appreciate that I could
set up a URL on my own server that proxies the request to Google
Charts, but I'm looking for a purely client-side solution.

And two, if I use a SCRIPT tag that points to the chart URL with
chof=json then I get back a JSON object string. But I cannot parse or
execute it as I cannot grab the contents of a SCRIPT tag when its
"src" attribute is being used (i.e. the innerHTML of the SCRIPT
returns "").

If there was a chof=jsonp, then I could pass the name of a Javascript
function to be executed with the chart JSON data as a parameter.


For example, the URL:

http://chart.apis.google.com/chart?cht=bvg&chs=250x150&chd=s:Monkeys&chxt=x,y&chxs=0,ff0000,12,0,lt|1,0000ff,10,1,lt&chof=jsonp&methodName=useResults

Would return:

useResults({"chartshape":[ ... ]})

which would be executed within the context of my page, and pass me the
JSON data.


Does anyone else think this feature would be useful, or know if there
is an alternative?

Thanks.

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