Buffer distance

[flightsurvey]

I have created a buffer around a geojson object in Leaflet in the following way:

var geoJSON ={
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              -4.491606,
              54.143007
            ],
            [
              -4.499331,
              54.139085
            ],
            [
              -4.497614,
              54.13828
            ],
            [
              -4.495983,
              54.139135
            ],
            [
              -4.495296,
              54.138783
            ],
            [
              -4.490061,
              54.141146
            ],
            [
              -4.491606,
              54.143007
            ]
          ]
        ]
      }
    }
  ]
};

var area = L.geoJSON(JSON.parse(geoJSON)), {
	color: 'green',
	weight: 2,
	onEachFeature: function (feature, layer) {
		layer.on("click", function (e) {
			map.fitBounds(layer.getBounds());
		});
	}
}).addTo(map);

var distance = 50;

var buffer = L.geoJSON(turf.buffer(JSON.parse(area), distance / 1000, {units:'kilometers'}), {
	color: 'orange',
	weight: 2,
	onEachFeature: function (feature, layer) {
		layer.on("click", function (e) {
			map.fitBounds(layer.getBounds());
		});
	}
}).addTo(map);

I then measured a perpendicular line between the area and the buffer - albeit freehand but it seems to be pretty true - and it appears to be around 44m.

To view the output paste the following into geojson.io:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              -4.491008208047599,
              54.14317729554968
            ],
            [
              -4.4910793289379,
              54.14324457294276
            ],
            [
              -4.491172202002483,
              54.14330203846458
            ],
            [
              -4.491282991531243,
              54.14334731869702
            ],
            [
              -4.4914071217792,
              54.14337854349127
            ],
            [
              -4.4915394659636,
              54.14339442321583
            ],
            [
              -4.491674558029246,
              54.14339430202498
            ],
            [
              -4.4918068184314475,
              54.14337818494692
            ],
            [
              -4.491930784606396,
              54.14334673767213
            ],
            [
              -4.492041336604907,
              54.143301259052194
            ],
            [
              -4.499766330943429,
              54.139379210582064
            ],
            [
              -4.499855281221839,
              54.139324303903805
            ],
            [
              -4.499924414426821,
              54.13926035213715
            ],
            [
              -4.4999711175876955,
              54.139189772565246
            ],
            [
              -4.49999362558707,
              54.139115232965906
            ],
            [
              -4.499991087854817,
              54.139039550771095
            ],
            [
              -4.499963600490543,
              54.13896558657387
            ],
            [
              -4.499912202604401,
              54.138896136007745
            ],
            [
              -4.4998388370186895,
              54.13883382408492
            ],
            [
              -4.4997462768187315,
              54.13878100598601
            ],
            [
              -4.498029287924673,
              54.137976015172434
            ],
            [
              -4.497917507036294,
              54.137933615722105
            ],
            [
              -4.497793541787066,
              54.13790512215984
            ],
            [
              -4.497662368762999,
              54.137891678365825
            ],
            [
              -4.497529253887912,
              54.13789382405563
            ],
            [
              -4.497399541047021,
              54.13791147311333
            ],
            [
              -4.497278437580579,
              54.137943917044495
            ],
            [
              -4.497170805253291,
              54.1379898534117
            ],
            [
              -4.495977972533194,
              54.13861515582364
            ],
            [
              -4.495733558522022,
              54.138489923952314
            ],
            [
              -4.495627491604399,
              54.1384455270722
            ],
            [
              -4.495508672456908,
              54.138414112723275
            ],
            [
              -4.495381671944031,
              54.138396889388886
            ],
            [
              -4.495251375637127,
              54.138394519645125
            ],
            [
              -4.49512279589262,
              54.13840709467304
            ],
            [
              -4.495000879053287,
              54.138434130748365
            ],
            [
              -4.494890315185861,
              54.138474587844314
            ],
            [
              -4.4896553212314725,
              54.140837556173345
            ],
            [
              -4.4895608621765035,
              54.140889530204326
            ],
            [
              -4.489485414002924,
              54.14095125325352
            ],
            [
              -4.489431844752228,
              54.14102037914921
            ],
            [
              -4.489402190854689,
              54.1410942803016
            ],
            [
              -4.489397579698279,
              54.14117014757768
            ],
            [
              -4.489418186747154,
              54.14124509708067
            ],
            [
              -4.489463228844416,
              54.14131627977578
            ],
            [
              -4.491008208047599,
              54.14317729554968
            ]
          ]
        ]
      }
    },
    {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              -4.491606,
              54.143007
            ],
            [
              -4.499331,
              54.139085
            ],
            [
              -4.497614,
              54.13828
            ],
            [
              -4.495983,
              54.139135
            ],
            [
              -4.495296,
              54.138783
            ],
            [
              -4.490061,
              54.141146
            ],
            [
              -4.491606,
              54.143007
            ]
          ]
        ]
      }
    },
    {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "LineString",
        "coordinates": [
          [
            -4.4956934452056885,
            54.14144647026728
          ],
          [
            -4.49527233839035,
            54.14114479855208
          ]
        ]
      }
    }
  ]
}

Would anyone like to comment on this? I am quite happy to accept that my implementation is wrong but at the moment it doesn't seem to be to me.

[rowanwins]

Hi @flightsurvey

Sorry for the slow reply, in Australia this is our summer holiday period and so my contributions and support have slowed.

So are you wanting a buffer of 50m and you're saying that the result if 44m?

There are some known issues in the buffer module at the moment. #1470 outlines a breaking change that was made a while ago so you might be best of revert back to the version specified version in that issue.

Hope that helps,
Rowan

[flightsurvey]

Hi Rowan,

Thank you very much for the insight. I'll have a look at your suggestion and, in the meantime, enjoy the sunshine.

Cheers,
Paddy

[chrispahm]

Hi @flightsurvey @rowanwins @mfedderly ,

trying to help to clean up some older issues here: This bug has been resolved with Turf v6.2.0 (and later) as highlighted in the following notebook
https://observablehq.com/@chrispahm/turf-issue-1547

So I guess this issue can be closed?

[JamesLMilner]

Again thanks @chrispahm - as you have shown the fix we can close this out. Any related problems can be raised in a new issue.