webread with json parameters

Hello,

I am trying to dowload climatic data from the ACIS Web Services (http://www.rcc-acis.org/docs_webservices.html). Specifically, I would need data for the average temperatures, at daily frequency, for each US state from 1960 until today.

My json parameter vector should be the following (e.g., for DC),

'{"state":"dc","sdate":"1960-01-01","edate":"2020-10-01","grid":"1","elems":[{"name":"avgt","interval":"dly","duration":"dly","area_reduce":"state_mean"}]}'

In Matlab I tried to use the webread function as follows

url = 'http://data.rcc-acis.org/GridData';
D1 = datetime(1999,01,01,'Format','yyyy-MM-dd');
D2 = datetime(2020,01,01,'Format','yyyy-MM-dd');
opzelem=['name','avgt','interval','dly','duration','dly','area_reduce','state_mean'];
scarico = webread(url,'state','DC','sdate',D1,'edate',D2,'grid','1','elems',opzelem);

but this returns the following error:

Error using readContentFromWebService (line 46)
The server returned the status 400 with message "Bad Request" in response to the request to URL
http://data.rcc-acis.org/GridData?state=DC&sdate=1999-01-01&edate=2020-01-01&grid=1&elems=nameavgtintervaldlydurationdlyarea_reducestate_mean.

Basically, I do not know how to include the "elems" options into webread. Using the jsondecode function to construct a struct array from the json parameter vector does not work either because webread only admits name-value pairs, not structures. Do you have any idea of how to solve it? thank you very much

Answer 1

[Ive J]

elems itself should be added as a nested struct to the input data, try this

headers = {'Content-Type' 'application/json'; 'Accept' 'application/json'};
options = weboptions('HeaderFields', headers, 'Timeout', 5000);
data = struct('state', "dc", 'sdate', "1990101", 'edate', "20200101", 'grid', "3");
data.elems = {struct('name', "maxt",'area_reduce', "state_mean")};
scarico  = webwrite('http://data.rcc-acis.org/GridData', data, options);

[Filippo Natoli]

Thanks Ive Ive, it works perfectly!