Having trouble with Mapbox Isochrone FeatureCollection return type

Question

I'm making a call to the Mapbox Isochrone API to obtain a FeatureCollection with this code:

string getIso = lng.ToString() + ","
          + lat.ToString() 
          + "?contours_minutes=" + minutes.ToString()
          + "&polygons=true"
          + "&denoise=" + denoiseValue.ToString()
          + "&generalize=" + generalizeValue.ToString()
          + "&access_token=" + _appSettings.MapboxAccessToken;

HttpClient client = new HttpClient();
client.BaseAddress = new Uri(drivetimeURL);

HttpResponseMessage response = client.GetAsync(getIso).Result;
FeatureCollection dtPolygon = await response.Content.ReadFromJsonAsync<FeatureCollection>();

I'm trying to get the data as a FeatureCollection type using the GeoJson.Net library, but when I run the code, all I get is basically an empty object:

{
    "type": 8,
    "features": [],
    "boundingBoxes": null,
    "crs": null
}

If I run this:

https://api.mapbox.com/isochrone/v1/mapbox/driving/-118.22258,33.99038?contours_minutes=10&polygons=true&denoise=1&generalize=1&access_token=XXXXXXXXXXXXXX

here's what I get and this is what I need in an object (coordinates mostly removed):

{
    "features": [
        {
            "properties": {
                "fill": "#bf4040",
                "fillOpacity": 0.33,
                "fill-opacity": 0.33,
                "fillColor": "#bf4040",
                "color": "#bf4040",
                "contour": 10,
                "opacity": 0.33,
                "metric": "time"
            },
            "geometry": {
                "coordinates": [
                    [
                        [
                            -118.21958,
                            34.026152
                        ],
                        [
                            -118.220031,
                            34.025831
                        ],
                        [
                            -118.22058,
                            34.025474
                        ]
                    ]
                ],
                "type": "Polygon"
            },
            "type": "Feature"
        }
    ],
    "type": "FeatureCollection"
}

I suspect that I'm not completely understanding how GEOJson works and that I may have to manipulate the response from Mapbox to get it into a type that has the details. Or do I need to create a custom class/model that mimics the Mapbox response?

Answer 1

I think you can try to read as JSON first, then deserialize:

HttpResponseMessage response = client.GetAsync(getIso).Result;
string jsonResponse = await response.Content.ReadAsStringAsync();
FeatureCollection dtPolygon = JsonConvert.DeserializeObject<FeatureCollection>(jsonResponse);