How to place squares along the line? (Geojson+mapbox)

Question

I have a rectangular and need to fill it with squares. I find the center line and want to place the squares along that line. But is there any simple method to draw a square in mapboxgl with any other libs like turfjs? Like set the center of the square and a side length and get a coordinates of the square? Any ideas? As placing circles with geojson is not a problem, but looks like a problem for me with squares, as I have to calculate 4 coordinates.

Answer 1

With turf you got the right tool at hand to solve this task.

One way of doing it would be something like this:

1. Get the line distance

2. Divide the line distance with the amount of rectangles you want

3. Use turf.along() to get a point along your line

4. Use turf.buffer, turf.bbox and turf.bboxPolygon to get a rectangle on the point location

5. Draw everything onto the map via mapbox-gl-js

Here is a code example. You can hit "run code snippet" to show the result.

https://jsfiddle.net/andi_lo/3rc6vca3/

mapboxgl.accessToken = 'pk.eyJ1IjoiZmFyYWRheTIiLCJhIjoiTUVHbDl5OCJ9.buFaqIdaIM3iXr1BOYKpsQ';

var map = new mapboxgl.Map({
  container: 'map',
  style: 'mapbox://styles/mapbox/streets-v9',
  center: [-74.10931699675322, 4.61336863727521],
  zoom: 11,
});

map.on('load', () => {
  map.addSource('line', {
    'type': 'geojson',
    'data': {
      'type': 'FeatureCollection',
      'features': [],
    },
  });

  map.addSource('rect', {
    'type': 'geojson',
    'data': {
      'type': 'FeatureCollection',
      'features': [],
    },
  });

  map.addLayer({
    id: 'line_layer',
    source: 'line',
    type: 'line',
    paint: {
      'line-width': 3,
      'line-color': '#333',
    },
  });

  map.addLayer({
    id: 'rect_layer',
    source: 'rect',
    type: 'fill',
    paint: {
      'fill-color': '#00b7bf',
    },
  });

  const line = turf.lineString([[-74.07, 4.66], [-74.17, 4.56]]);
  const lineCollection = turf.featureCollection([line]);
  const lineDistance = turf.lineDistance(line);
  const rectCollection = turf.featureCollection([]);

  const RECT_COUNT = 7;
  const RECT_SIZE = 0.6;
  const BUFFER_STEPS = 32;
  const SEGMENTS = lineDistance / RECT_COUNT;
  const UNITS = 'kilometers';
  for(let i = 0; i <= RECT_COUNT; i++) {
    const point = turf.along(line, (SEGMENTS * i), UNITS);
    const buffered = turf.buffer(point, RECT_SIZE, UNITS, BUFFER_STEPS);
    const bbox = turf.bbox(buffered);
    const bboxPolygon = turf.bboxPolygon(bbox);
    rectCollection.features.push(bboxPolygon);
  }

  map.getSource('line').setData(lineCollection);
  map.getSource('rect').setData(rectCollection);
});

#map {
  height: 500px;
}

<link href="https://api.tiles.mapbox.com/mapbox-gl-js/v0.38.0/mapbox-gl.css" rel="stylesheet"/>
<script src="https://api.tiles.mapbox.com/mapbox-gl-js/v0.38.0/mapbox-gl.js"></script>
<script src="https://npmcdn.com/@turf/[email protected]/turf.min.js"></script>

<div id="map"></div>