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D3 function for fitting a projection to geodata
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| import d3 from 'd3'; | |
| export const fitProjection = (projection, data, box, center) => { | |
| // get the bounding box for the data - might be more efficient approaches | |
| let left = Infinity; | |
| let bottom = -Infinity; | |
| let right = -Infinity; | |
| let top = Infinity; | |
| // reset projection | |
| projection.scale(1).translate([0, 0]); | |
| data.features.forEach((feature) => { | |
| d3.geo.bounds(feature).forEach((coords) => { | |
| const [x, y] = projection(coords); | |
| if (x < left) left = x; | |
| if (x > right) right = x; | |
| if (y > bottom) bottom = y; | |
| if (y < top) top = y; | |
| }); | |
| }); | |
| // project the bounding box, find aspect ratio | |
| const width = (bb) => (bb[1][0] - bb[0][0]); | |
| const height = (bb) => (bb[1][1] - bb[0][1]); | |
| const aspect = (bb) => width(bb) / height(bb); | |
| const startbox = [[left, top], [right, bottom]]; | |
| const widthDetermined = aspect(startbox) > aspect(box); | |
| const scale = widthDetermined ? | |
| // scale determined by width | |
| width(box) / width(startbox) : | |
| // scale determined by height | |
| height(box) / height(startbox); | |
| // set x translation | |
| let transX = box[0][0] - startbox[0][0] * scale; | |
| // set y translation | |
| let transY = box[0][1] - startbox[0][1] * scale; | |
| // center if requested | |
| if (center) { | |
| if (widthDetermined) { | |
| transY = transY - (transY + startbox[1][1] * scale - box[1][1]) / 2; | |
| } else { | |
| transX = transX - (transX + startbox[1][0] * scale - box[1][0]) / 2; | |
| } | |
| } | |
| return projection.scale(scale).translate([transX, transY]); | |
| }; |
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