Is directions Api not accepting negative values for coordinates ? Flutter - json

Question

I'm sending a direction request to an API and I'm facing this problem.
With coordinates as flutter: start location is :latitude 37.33101308, longitude -122.03065487 and end location is :latitude 37.33097983, longitude -122.03063943 the - symbol creates a problem.
When sending the resulting request
http://www.yournavigation.org/api/1.0/gosmore.php?format=geojson&v=bicycle&fast=0&layer=mapnik&flat=37.33101308&flon=-122.03065487&tlat=37.33097983&tlon=-122.03063943&geometry=1&instructions=1&lang=it
I get an error that I'm not yet able to understand:
[VERBOSE-2:ui_dart_state.cc(157)] Unhandled Exception:
FormatException: Unexpected character (at character 1) ^
0 _ChunkedJsonParser.fail (dart:convert-patch/convert_patch.dart:1394:5)
1 _ChunkedJsonParser.parseNumber (dart:convert-patch/convert_patch.dart:1261:9)
2 _ChunkedJsonParser.parse (dart:convert-patch/convert_patch.dart:926:22)
3 _parseJson (dart:convert-patch/convert_patch.dart:31:10)
4 JsonDecoder.convert (dart:convert/json.dart:495:36)
5 JsonCodec.decode (dart:convert/json.dart:153:41)
6 jsonDecode (dart:convert/json.dart:96:10)
7 DirectionsRepository.postRequest (package:fixit_cloud_biking/directions/directions_repository.dart:39:26)
8 DirectionsBloc.getDirections (package:fixit_cloud_biking/directions/directions_bloc.dart:46:12)
9 _AsyncStarStreamController.runBody (dart:async-patch/async_patch.dart:155:5)
10 _rootRun (dart:async/zone.dart:1122:3<…>
Is it because of a json formatting issue or does it means that www.yournavigation.org/api doesn't accept negative coordinates values ?
This error doesn't happen if the sent request has positive coordinates as this
'http://www.yournavigation.org/api/1.0/gosmore.php?format=geojson&v=bicycle&fast=0&layer=mapnik&flat=44.5018645003438&flon=11.340018709036542&tlat=44.502138&tlon=11.340402&geometry=1&instructions=1&lang=it'
Just for testing I tried just making them positive coordinates with .abs(). but of course the results is a wrong location on the map.
Is there another coordinate system that has all positive values?
Thank you very much for your help.
This is the class I'm sending the request from:
import 'package:http/http.dart';
import 'package:latlong/latlong.dart';
import 'dart:convert' as convert;
import 'dart:math';
class DirectionsRepository {
Future<List<LatLng>> postRequest(LatLng start, LatLng end) async {
print('postRequest() called');
print(
'start location is :latitude ${start.latitude}, longitude ${start.longitude}');
print(
'end location is :latitude ${end.latitude}, longitude ${end.longitude}');
// NORMAL NEGATIVE LONGITUDE THROWS = API ERROR:
// format error [VERBOSE-2:ui_dart_state.cc(157)] Unhandled Exception: FormatException: Unexpected character (at character 1)
String flat = (start.latitude).toString();
String flon = (start.longitude).toString();
String tlat = (end.latitude).toString();
String tlon = (end.longitude).toString();
// ALL POSITIVE VALUES DON'T THROW AN ERROR BUT IS WRONG PLACE
// String flat = (start.latitude).abs().toString();
// String flon = (start.longitude).abs().toString();
// String tlat = (end.latitude).abs().toString();
// String tlon = (end.longitude).abs().toString();
final request =
'http://www.yournavigation.org/api/1.0/gosmore.php?format=geojson&v=bicycle&fast=0&layer=mapnik&flat=$flat&flon=$flon&tlat=$tlat&tlon=$tlon&geometry=1&instructions=1&lang=it';
print('final request is $request');
// working properly
// final request =
// 'http://www.yournavigation.org/api/1.0/gosmore.php?format=geojson&v=bicycle&fast=0&layer=mapnik&flat=44.5018645003438&flon=11.340018709036542&tlat=44.502138&tlon=11.340402&geometry=1&instructions=1&lang=it';
// Await the http get response, then decode the json-formatted response.
var response = await get(request);
if (response.statusCode == 200) {
var jsonResponse = convert.jsonDecode(response.body);
print('${jsonResponse.runtimeType} : $jsonResponse');
List<dynamic> coordinates = jsonResponse['coordinates'];
print('coordinates are : $coordinates');
print('coordinates are: ${coordinates.length}');
Map<String, dynamic> properties = jsonResponse['properties'];
// print('properties are $properties');
String distance = properties['distance'];
print('Route is $distance Km long.');
String instructions = properties['description'];
print('instructions are $instructions');
List<LatLng> suggestedRoute = [];
for (int i = 0; i < (coordinates.length); i++) {
dynamic coordinate = coordinates[i];
LatLng position = LatLng(coordinate[1], coordinate[0]);
suggestedRoute.add(position);
print('position is $position');
print(i);
}
print('postRequest() suggestedRoute is $suggestedRoute');
return suggestedRoute;
} else {
print(
'postRequest() Request failed with status: ${response.statusCode}.');
}
}
}

Answer 1

After a few tries, I've nailed down the problem to be a direction API server problem. So, request is fine, but method's json decoding just fails because gets a 242 response status code which passes the check but fails as the response body does not match what's handled in the method.