From bf95149e9cd6aac2abfb97269ecc209b3b202088 Mon Sep 17 00:00:00 2001
From: Dmitry Shirokov <deadrunk@gmail.com>
Date: Mon, 5 Jan 2026 11:00:51 +1100
Subject: [PATCH] fix: precision for 3d points

---
 src/dataset/mapshaper-layer-utils.mjs |  5 ++++-
 src/geom/mapshaper-rounding.mjs       |  6 ++++--
 test/geojson-test.mjs                 | 14 +++++++++++++-
 3 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/dataset/mapshaper-layer-utils.mjs b/src/dataset/mapshaper-layer-utils.mjs
index 24b2b6e7f..817cd2b1d 100644
--- a/src/dataset/mapshaper-layer-utils.mjs
+++ b/src/dataset/mapshaper-layer-utils.mjs
@@ -86,9 +86,12 @@ export function deleteFeatureById(lyr, i) {
 export function transformPointsInLayer(lyr, f) {
   if (layerHasPoints(lyr)) {
     forEachPoint(lyr.shapes, function(p) {
-      var p2 = f(p[0], p[1]);
+      var p2 = f(p[0], p[1], p[2]);
       p[0] = p2[0];
       p[1] = p2[1];
+      if (p[2] !== undefined) {
+        p[2] = p2[2];
+      }
     });
   }
 }
diff --git a/src/geom/mapshaper-rounding.mjs b/src/geom/mapshaper-rounding.mjs
index 1f96f5b51..eca257d84 100644
--- a/src/geom/mapshaper-rounding.mjs
+++ b/src/geom/mapshaper-rounding.mjs
@@ -100,8 +100,10 @@ export const fround = Math.fround || fround2;
 export function setCoordinatePrecision(dataset, precision, fixGeom) {
   var round = getRoundingFunction(precision);
   var repairArcs = dataset.arcs && fixGeom ? getRepairFunction(dataset.arcs) : null;
-  transformPoints(dataset, function(x, y) {
-    return [round(x), round(y)];
+  transformPoints(dataset, function(x, y, z) {
+    return (z !== undefined)
+      ? [round(x), round(y), round(z)]
+      : [round(x), round(y)];
   });
   if (repairArcs) {
     repairArcs(dataset.arcs);
diff --git a/test/geojson-test.mjs b/test/geojson-test.mjs
index 40c5e7ca9..cdb93a14f 100644
--- a/test/geojson-test.mjs
+++ b/test/geojson-test.mjs
@@ -425,7 +425,19 @@ describe('mapshaper-geojson.js', function () {
         var output = await api.applyCommands(cmd, {'point.json': input});
         var json = JSON.parse(output['point.json'])
         var coords = json.geometries[0].coordinates;
-        assert.deepEqual(coords, [[4,4],[0.123457,-9.876543]]);
+        assert.deepEqual(coords, [[4, 4],[0.123457, -9.876543]]);
+      });
+
+      it('set coordinate precision to 6 decimals - with 3d points', async function() {
+        var input = {
+          type: 'MultiPoint',
+          coordinates: [[4.000000000000001, 3.999999999999, 5.0000000000001], [0.123456789,-9.87654321, 0.5678901234]]
+        };
+        var cmd = '-i point.json -o precision=0.000001';
+        var output = await api.applyCommands(cmd, {'point.json': input});
+        var json = JSON.parse(output['point.json'])
+        var coords = json.geometries[0].coordinates;
+        assert.deepStrictEqual(coords, [[4, 4, 5],[0.123457, -9.876543, 0.56789]]);
       });
     });