Easier usage with d3.geoProject?

[mbostock]

It’d be nice if this library were easier to use when saving spherically-clipped GeoJSON. For example:

https://beta.observablehq.com/d/d706c7f9c6e46907

The tedious parts are:

• You need to wrap the d3.geoClipPolygon instance with an object that has a stream method.

• You need to compose the d3.geoClipPolygon instance with streams that transform from degrees to radians and then back again.

Part of me wonders if it’s worth revisiting a more composable geographic projection pipeline…

(Also, I think d3.geoProject sometimes breaks polygon semantics, but that’s a separate issue.)

[Fil]

Yes; it would be nice to have this also for clipAngle — in your notebook it works by using:

{
  const clipAngle = d3.geoClipCircle(50/180*Math.PI);
  return d3.geoProject(land, {stream: stream => radians(clipAngle(degrees(stream)))});
}

(So maybe an issue to solve in d3-geo-projection rather than d3-geo-polygon.)

We should also account for rotation.

Since your code is working, is it not just a question of defining a syntax?

The polygon issue is similar to https://github.com/d3/d3-geo-projection/pull/146#issuecomment-415946484 : d3.geoProject is not meant to be used to project to spherical coordinates.

[mbostock]

Yep, an issue of syntax and abstraction. I would love to revisit the composable geographic projection pipeline idea. I wonder if there is some progress to be made there.