d3.js - How to automatically get the scale for a d3.geo.mercator projection with the topojson's bbox? -

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i have topojson file created --bbox flag, figured out how center (where b bbox):

var center = [(b[0] + b[2]) / 2, (b[1] + b[3]) / 2]

then calculated scale, problem calculated equirectangular projection (because it's easy enough):

var wscale = width  / (math.abs(b[0] - b[2]) / 360) / 2 / math.pi var hscale = height / (math.abs(b[1] - b[3]) / 360) / 2 / math.pi var scale = math.min(wscale, hscale)

equirectangular straya

i can't find way calculate mercator projection. i've seen this answer , tried use projection scale , directly set new scale:

projection = d3.geo.mercator()     .translate([width / 2, height / 2])     .center(center)     .scale(1)  [b0, b1] = projection([b[0], b[1]]) [b2, b3] = projection([b[2], b[3]]) scale = 1 / math.max(math.abs(b2 - b0) / width, math.abs(b3 - b1) / height)  projection.scale(s)

but result isn't perfect (poor tasmania):

sad mercator straya

edit: should have post in https://gis.stackexchange.com/ or here fine ?


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