Needs modification to work with d3 v3 about topogram HOT 7 CLOSED

👍 I don't mind working on a pull request if anyone can hint about a possible cause.

from topogram.

The problem seems to be that v3's projection functions work differently than v2's. @mbostock, can you provide a hint?

from topogram.

https://github.com/mbostock/d3/wiki/3.0
https://github.com/mbostock/d3/wiki/Upgrading-to-3.0

from topogram.

Thanks for the hints. Every 32nd point (with a few exceptions), the algorithm seems to insert a diagonally offset coordinate:

Point 1: M738.6410891318739,288.6117802470147
18.64099944406587,-71.38842446507579
18.640909754354652,-71.38862917712373
[...]
-1.089590636644175,-84.48670347140757
-1.090580345942044,-84.48688700598365
Point 33: 718.9084298790658,275.5129294610754
-1.0919136122784039,-84.48703876147886
-1.0922570996749528,-84.48700698383607
[...]
Point 65: 702.9690598895354,277.89646070245584
-17.030943323429927,-82.10357075652627
-17.030946536420732,-82.1036022155083
[...]
Point 97: 702.6845670620858,275.83483610874566

I haven't been able to find the solution yet but will look deeper into the mapping of arcs to screen space:

Row 38: // project the arcs into screen space
      var tf = transformer(topology.transform),
          projectedArcs = topology.arcs.map(function(arc) {
            var x = 0, y = 0;
            return arc.map(function(coord) {
              coord[0] = (x += coord[0]);
              coord[1] = (y += coord[1]);
              return projection(tf(coord));
            });
          });

@shawnbot: What do you think?

from topogram.

I would probably use the browser's debugger to step through the code as it is running to understand what is happening. There could be many reasons why this isn't working, and without being familiar with the code it's difficult for me to say what the problem is.

I suspect it might be caused by d3.geo's adaptive resampling of the projection, which detects areas of distortion. When you pass in a bare function as the projection to d3.geo.path, it gets wrapped in a resampling projection stream (see d3_geo_pathProjectStream); an instance of d3.geo.projection in contrast adds rotation and clipping, in addition to resampling, to the projection stream.

Adaptive resampling requires that the geometry being transform is expressed in spherical coordinates, so if you pass in Cartesian coordinates, you're going to have a bad time. If you want to use the identity projection (i.e., pass projected Cartesian coordinates to d3.geo.path and disable resampling), then in V3 you should set path.projection(null) rather than passing in the identity function. Otherwise the adaptive resampling will introduce intermediate points in your geometry using great-arc interpolation, because it assumes each polygonal segment is a great arc.

from topogram.

Thanks @mbostock! Passing null instead of the identity was all it took. Have submitted the fix.

from topogram.

💥

from topogram.