It’d be convenient to allow the feature to be specified as a name, e.g.

topojson.feature(topology, "foo")

would be equivalent to

topojson.feature(topology, topology.objects.foo)

Hi, are you planning to adopt ESM?

Thanks!

• topojson.bbox (return new bbox)
• topojson.quantize (clone arcs)
• topojson.transform (return new point)
• topojson.untransform (return new point)

Related topojson/topojson#86.
Related topojson/topojson-simplify#5.
Related topojson/topojson-server#2.

Related #7.

If an arc collapses down to a single point during quantization, we add a [0,0] at the end to ensure that each arc has at least two points, per the specification. The problem with this is that it implicitly drops any additional dimensions (beyond x and y) of the coincident points.

So, it’d be better to add the last point p instead of making a new point [0,0], so that any additional dimensions in the last point p are preserved. This assumes that the input arc has at least two points, but that should be a reasonable assumption given the specification.

If there are more than two geometries in a collection that share the same arcs, the mesh filter function will ignore some neighboring geometries.

For instance, given the following topology, the filter function will never be passed geometry with id 2.

var topology = {
  "type": "Topology",
  "objects": {
    "collection": {
      "type": "GeometryCollection",
      "geometries": [
        {"id": 1, "type": "LineString", "arcs": [0,1]},
        {"id": 2, "type": "LineString", "arcs": [0,1]},
        {"id": 3, "type": "LineString", "arcs": [0,1]}
      ]
    }
  },
  "arcs": [
    [[1, 0], [2, 0]],
    [[0, 0], [1, 0]]
  ]
};

topojson.mesh(topology, topology.objects.collection, function (geometry, neighbor) {
  return geometry.id === 2 || neighbor.id === 2;
});

For a more practical use case, in the screenshot below the bold line is created with a mesh filter intend to outline Uganda. However, since Uganda shares borders with both Kenya and Kenya’s states, the filter fails and the border is partially missing.

The issue appears to be in the extractArcs function (https://github.com/topojson/topojson-client/blob/master/src/mesh.js#L50) where only the first and last neighbors are sent to the filter function.

Here are some possible solutions that I could think of:

• pass all geometries as a third argument to the filter function.

function(geoms) { if (filter(geoms[0].g, geoms[geoms.length - 1].g, geoms.map(function(geom) { return geom.g; })) arcs.push(geoms[0].i); });

• only pass all geometries to the filter function.

function(geoms) { if (filter(geoms.map(function(geom) { return geom.g; }))) arcs.push(geoms[0].i); });

• pass each geometry as an individual argument to the filter function

function(geoms) { if (filter.apply(this, geoms.map(function(geom) { return geom.g; }))) arcs.push(geoms[0].i); });

• allow the way the filter function is applied to be changed as an optional argument to the mesh function

topojson.mesh(topology, object, filter, [apply = defaultApply])

function defaultApply(geometries, filterFn) {
  return geometries.reduce(function (accum, geom, i, geoms) {
    if (accum === false) return false;
    return filterFn(geoms[0], geom);
  }, true);
}

function (geoms) { 
  var apply = apply || defaultApply;
  if(apply(geoms.map(function(geom) { return geom.g; }), filter) arcs.push(geoms[0].i); 
});

If the input is polygons, it should use topojson.mergeArcs.

If the input is lines, it should use topojson.meshArcs.

https://github.com/topojson/topojson/blob/v1.6.27/bin/topojson-merge

Related topojson/topojson#112.

Because I am working with both right now, I am wondering why links objects (from d3.force) and neighbors objects (from d3.geo) are structured differently, whereas they are substantially equivalent.

Since neighbors are, to my knowledge, not used directly in any subsequent functions, I would suggest to structure them as links objects.

I am trying to render districts outlines on a map using updated topojson file which I created from geojson file.

I successfully made the original file create map using d3. Bu then, I added more features created using "geojson.io". I did so by exporting features in geojson format, appending them to original districts geojson file and then finally converting the updated geojson file to topojson using geo2topo. cli

The new topojson file seems to run perfectly on "geojson.io", "mapShaper". But in my app, on passing the topology and topojson object to topojson-client's feature method, it returns undefined.

I've checked the initial topojson file with new one. All the keys/ values are there, and that because latter works on above mentioned sites. I've been forced to believe there is some bug in the method which is returning undefined.

Right now, the only way to add use the the topojson-client is to import it like this:

import * as topojson from "topojson-client";

What if we export it in a way that we can use it like:

import topojson from "topojson-client";

I expected topomerge to be able to deduplicate geometries but it didn't work:

topomerge -k 'd.id' < foo.json

Geometries come out like this:

{"type":"MultiPolygon","arcs":[[]],"id":"1"}
// etc.

As a workaround I used ndjson-reduce 'p[d.id] = d, p' '{}' | ndjson-split 'Object.values(d)' on the GeoJSON features first.

It’d be nice to have a binary for taking projected, planar TopoJSON as input and then modifying the transform (or computing the transformed coordinates, if there is no transform) so that the TopoJSON fits in the desired bounding box. It should also support --invert for flipping the y-dimension, as Proj4 and other projection systems typically use the other y direction than Canvas and SVG.

https://github.com/topojson/topojson/blob/v1.6.27/lib/topojson/scale.js

https://observablehq.com/@observablehq/plot-state-labels

I have multiple TopoJSON files representing different layers within the same overall shape, and I would like to merge them into one file
together for easier future use(keep multiple objects), similar to the effect achieved "us-counties-10m.json" file in above link.

Currently topojson.mesh() returns one big mesh, and no simple way to extract borders and tag them by neighbors (for example).

Could it be interesting to have an extension of topojson.mesh() that allows a tag(a,b) function to partition the resulting mesh?

Here's a block that demonstrates the idea (with code adapted from src/mesh.js):
http://blockbuilder.org/Fil/9ff0ca1825369075394d0e77e149052c

Notice how the two lines between USA and Canada belong to the same MultiLineString (they have the same tag). The coastline is tagged 0 and also is a unique MultiLineString.

This gist reproduces the issue: https://gist.github.com/noffle/aad0b1db44a2e443b8c64897897064d0

There are three large Polygons, which produce a MultiPolygon when merged. However, each LinearRing inside does not repeat the first coordinates as the last coordinates as per the GeoJSON spec. This issue doesn't seem to appear with all merges, just this particular case. I notice that if I remove the 3rd polygon, this issue is no longer reproduced.

I have a minor nudge.

var stitchedArcs = {}

Looking at the life-cycle of the object stitchedArcs

It has the characteristics of a set ( i.e. a [key,value] pairs where the value is only ever set to '1' )

I would like to make this semantically more precise.

By semantically I mean I want to, lock this down, to give assurances that the value is never accidentally incremented or set to a a value like as 'socks'.

I am about to submit a three line PR

I have the topojson file in attachment:
topojson_issue.json.txt

which I made with the "pytopojson" library. I'm pretty confident it looks ok, library doesn't complain but I guess there isn't an online validator. Geojson-wise it's a feature collection of 20 multipolygons. I use the following snippet in javascript:

d3.json("https://75.119.131.164/data/hourly_homezones.json", function(error, topology) {
    console.log(topojson.feature(topology, topology.objects.my_geojson.geometries));
};

which returns:

I don't think this is an expected response. I expect a featurecollection of multipolygons.

Any foolish mistake I'm making ? Or is this a bug ?

One of the biggest performance costs in topojson.feature (and topojson.mesh) is calling array.slice on every point. There are times when this is needed, but in many cases it would be perfectly reasonable to modify the coordinates in-place when applying the transform, and to avoid the copy when creating a feature or mesh. We should design an appropriate API to enable this faster path.

Moved from topojson/topojson#215.

topojson.absolute([transform])

If the specified transform is non-null, returns a function that removes the delta-encoding from the specified arc and applies the specified transform. The specified arc coordinates are modified in-place, and the arc is returned. If the specified transform is null, returns the identity function.

topojson.relative(transform)

If the specified transform is non-null, returns a function that applies the delta-encoding to the specified arc and removes the specified transform. The specified arc coordinates are modified in-place, and the arc is returned. If the specified transform is null, returns the identity function.