Not able to create exact .json from a struct

Hello, I need to create a .json to make a request using an API. Using Python, it worked succesfully but with MATLAB I constantly get status 400 with "Bad Request". Since creating a .json in MATLAB is not as easy as in Python , I may be making some mistake creating the .json. Also, I already made another kind of request via MATLAB using .json to the same server, which worked fine. Here is the .json, that I need to create:

new_task = {
  "task_type": "area",
  "task_name": "area_request1",
  "params":
  {
    "dates": [
    {
      "startDate": "01-01-2018",
      "endDate": "02-14-2018"
    }],
    "layers": [
    {
      "layer": "SRTMGL3_DEM",
      "product": "SRTMGL3_NC.003"
    }],
    "output":
    {
      "format":
      {
        "type": "geotiff"
      },
      "projection": "geographic"
    },
    "geo":
    {
      "type": "FeatureCollection",
      "fileName": "User-Drawn-Polygon",
      "features": [
      {
        "type": "Feature",
        "properties":
        {},
        "geometry":
        {
          "type": "Polygon",
          "coordinates": [
            [
              [5, 12],
              [5, 13],
              [6, 13],
              [6, 12],
              [5, 12]
            ]
          ]
        }
      }]
    }
  }
}

And here is the code to construct it in MATLAB:

% Area example
area_json_struct = struct();
area_json_struct.task_type = "area";
area_json_struct.task_name = "area_request1";
%% json_struct -> params
% json_struct -> params -> dates
startDate = ["01-01-2018"];
endDate = ["01-02-2018"];
area_json_struct.params.dates = table(startDate, endDate);
% json_struct -> params -> layers
layer = ["SRTMGL3_DEM"];
product = ["SRTMGL3_NC.003"];
area_json_struct.params.layers = table(layer, product);
% json_struct -> params -> output
area_json_struct.params.output.format.type = "geotiff";
area_json_struct.params.output.projection = "geographic";
% json_struct -> params -> Geo
% Siehe https://de.wikipedia.org/wiki/GeoJSON
area_json_struct.params.geo.type="FeatureCollection";
area_json_struct.params.geo.fileName="User-Drawn-Polygon";

area_json_struct.params.geo.features.type = "Feature";
area_json_struct.params.geo.features.properties = table();
area_json_struct.params.geo.features.geometry.type = "Polygon";
area_json_struct.params.geo.features.geometry.coordinates = [...
              [5,12];...
              [5,13];...
              [6,13];...
              [6,12];...
              [5,12]...
            ];

area_payload = jsonencode(area_json_struct, 'PrettyPrint', true);

which results in:

area_payload =

    '{
       "task_type": "area",
       "task_name": "test",
       "params": {
         "dates": [
           {
             "startDate": "01-01-2018",
             "endDate": "01-02-2018"
           }
         ],
         "layers": [
           {
             "layer": "SRTMGL3_DEM",
             "product": "SRTMGL3_NC.003"
           }
         ],
         "output": {
           "format": {
             "type": "geotiff"
           },
           "projection": "geographic"
         },
         "geo": {
           "type": "FeatureCollection",
           "fileName": "User-Drawn-Polygon",
           "features": {
             "type": "Feature",
             "properties": [],
             "geometry": {
               "type": "Polygon",
               "coordinates": [
                 [
                   5,
                   12
                 ],
                 [
                   5,
                   13
                 ],
                 [
                   6,
                   13
                 ],
                 [
                   6,
                   12
                 ],
                 [
                   5,
                   12
                 ]
               ]
             }
           }
         }
       }
     }'

Thank you for any help!

[Geoff Hayes]

Mert - I see that in the output from MATLAB, you have

"properties": [],

whereas the initial json that you posted (from Python?) shows

"properties":
        {},

This may be a reason why there is a 400 error.

[Mert Asil Türeli]

Thank you for your answer! I also think that might be the problem but was not able to generate an output as

"properties":
        {},    

using

jsonencode

function. I tried it with empty cell, array and table. All of them gave me the squared brackets

[Geoff Hayes]

Try

area_json_struct.params.geo.features.properties = struct();

[Mert Asil Türeli]

Thank you that worked for brackets

[Geoff Hayes]

Was that the only issue?

[Mert Asil Türeli]

"features" also needed to be a table. Server returns now internal error instead of bad request. So I assume both .json's are now identical.

Answer 1

[Mert Asil Türeli]

I finally figured it out. If anyone else faces a similar issue in future, here is the code snippet to generate the .json below.

% Area example
area_json_struct = struct();
area_json_struct.task_type = "area";
area_json_struct.task_name = "test";

%% json_struct -> params
% json_struct -> params -> dates
startDate = ["01-01-2018"];
endDate = ["01-02-2018"];
area_json_struct.params.dates = table(startDate, endDate);

% json_struct -> params -> layers
layer = ["SRTMGL3_DEM"];
product = ["SRTMGL3_NC.003"];
area_json_struct.params.layers = table(layer, product);

% json_struct -> params -> output
area_json_struct.params.output.format.type = "geotiff";
area_json_struct.params.output.projection = "native";

% json_struct -> params -> Geo
area_json_struct.params.geo.type="FeatureCollection";
area_json_struct.params.geo.fileName="User-Drawn-Polygon";

%% features
type = "Feature";
properties = struct();
geometry.type = "Polygon";
geometry.coordinates = [...
              [5,12];...
              [5,13];...
              [6,13];...
              [6,12];...
              [5,12]...
            ];

area_json_struct.params.geo.features = table(type, properties, geometry);

area_payload = jsonencode(area_json_struct, 'PrettyPrint', true);

which prints:

area_payload =

    '{
       "task_type": "area",
       "task_name": "test",
       "params": {
         "dates": [
           {
             "startDate": "01-01-2018",
             "endDate": "01-02-2018"
           }
         ],
         "layers": [
           {
             "layer": "SRTMGL3_DEM",
             "product": "SRTMGL3_NC.003"
           }
         ],
         "output": {
           "format": {
             "type": "geotiff"
           },
           "projection": "native"
         },
         "geo": {
           "type": "FeatureCollection",
           "fileName": "User-Drawn-Polygon",
           "features": [
             {
               "type": "Feature",
               "properties": {},
               "geometry": {
                 "type": "Polygon",
                 "coordinates": [
                   [
                     5,
                     12
                   ],
                   [
                     5,
                     13
                   ],
                   [
                     6,
                     13
                   ],
                   [
                     6,
                     12
                   ],
                   [
                     5,
                     12
                   ]
                 ]
               }
             }
           ]
         }
       }
     }'