diff --git a/go.mod b/go.mod
index c402d7b..f5e360f 100644
--- a/go.mod
+++ b/go.mod
@@ -7,20 +7,25 @@ require (
 	github.com/deadsy/sdfx v0.0.0-20220428051248-ab3af168a1af
 	github.com/fogleman/fauxgl v0.0.0-20200818143847-27cddc103802
 	github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646
-	gonum.org/v1/gonum v0.11.0
+	gonum.org/v1/gonum v0.11.1-0.20220625074215-67f3e1dbfccc
 	gonum.org/v1/plot v0.11.0
 )
 
 require (
+	git.sr.ht/~sbinet/gg v0.3.1 // indirect
 	github.com/ajstarks/svgo v0.0.0-20211024235047-1546f124cd8b // indirect
 	github.com/dhconnelly/rtreego v1.1.0 // indirect
 	github.com/fogleman/simplify v0.0.0-20170216171241-d32f302d5046 // indirect
+	github.com/go-fonts/liberation v0.2.0 // indirect
+	github.com/go-latex/latex v0.0.0-20210823091927-c0d11ff05a81 // indirect
+	github.com/go-pdf/fpdf v0.6.0 // indirect
 	github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0 // indirect
 	github.com/hschendel/stl v1.0.4 // indirect
 	github.com/llgcode/draw2d v0.0.0-20200930101115-bfaf5d914d1e // indirect
 	github.com/yofu/dxf v0.0.0-20190710012328-5a6d1e83f16c // indirect
-	golang.org/x/exp v0.0.0-20191002040644-a1355ae1e2c3 // indirect
-	golang.org/x/image v0.0.0-20220302094943-723b81ca9867 // indirect
+	golang.org/x/exp v0.0.0-20220613132600-b0d781184e0d // indirect
+	golang.org/x/image v0.0.0-20220617043117-41969df76e82 // indirect
+	golang.org/x/text v0.3.7 // indirect
+	golang.org/x/tools v0.1.11 // indirect
 	rsc.io/pdf v0.1.1 // indirect
 )
-
diff --git a/go.sum b/go.sum
index 7859ca4..bb15cb7 100644
--- a/go.sum
+++ b/go.sum
@@ -1,5 +1,6 @@
 dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
 gioui.org v0.0.0-20210308172011-57750fc8a0a6/go.mod h1:RSH6KIUZ0p2xy5zHDxgAM4zumjgTw83q2ge/PI+yyw8=
+git.sr.ht/~sbinet/gg v0.3.1 h1:LNhjNn8DerC8f9DHLz6lS0YYul/b602DUxDgGkd/Aik=
 git.sr.ht/~sbinet/gg v0.3.1/go.mod h1:KGYtlADtqsqANL9ueOFkWymvzUvLMQllU5Ixo+8v3pc=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
@@ -28,14 +29,17 @@ github.com/fogleman/simplify v0.0.0-20170216171241-d32f302d5046/go.mod h1:KDwyDq
 github.com/go-fonts/dejavu v0.1.0/go.mod h1:4Wt4I4OU2Nq9asgDCteaAaWZOV24E+0/Pwo0gppep4g=
 github.com/go-fonts/latin-modern v0.2.0/go.mod h1:rQVLdDMK+mK1xscDwsqM5J8U2jrRa3T0ecnM9pNujks=
 github.com/go-fonts/liberation v0.1.1/go.mod h1:K6qoJYypsmfVjWg8KOVDQhLc8UDgIK2HYqyqAO9z7GY=
+github.com/go-fonts/liberation v0.2.0 h1:jAkAWJP4S+OsrPLZM4/eC9iW7CtHy+HBXrEwZXWo5VM=
 github.com/go-fonts/liberation v0.2.0/go.mod h1:K6qoJYypsmfVjWg8KOVDQhLc8UDgIK2HYqyqAO9z7GY=
 github.com/go-fonts/stix v0.1.0/go.mod h1:w/c1f0ldAUlJmLBvlbkvVXLAD+tAMqobIIQpmnUIzUY=
 github.com/go-gl/gl v0.0.0-20180407155706-68e253793080/go.mod h1:482civXOzJJCPzJ4ZOX/pwvXBWSnzD4OKMdH4ClKGbk=
 github.com/go-gl/glfw v0.0.0-20180426074136-46a8d530c326/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
 github.com/go-latex/latex v0.0.0-20210118124228-b3d85cf34e07/go.mod h1:CO1AlKB2CSIqUrmQPqA0gdRIlnLEY0gK5JGjh37zN5U=
+github.com/go-latex/latex v0.0.0-20210823091927-c0d11ff05a81 h1:6zl3BbBhdnMkpSj2YY30qV3gDcVBGtFgVsV3+/i+mKQ=
 github.com/go-latex/latex v0.0.0-20210823091927-c0d11ff05a81/go.mod h1:SX0U8uGpxhq9o2S/CELCSUxEWWAuoCUcVCQWv7G2OCk=
 github.com/go-pdf/fpdf v0.5.0/go.mod h1:HzcnA+A23uwogo0tp9yU+l3V+KXhiESpt1PMayhOh5M=
+github.com/go-pdf/fpdf v0.6.0 h1:MlgtGIfsdMEEQJr2le6b/HNr1ZlQwxyWr77r2aj2U/8=
 github.com/go-pdf/fpdf v0.6.0/go.mod h1:HzcnA+A23uwogo0tp9yU+l3V+KXhiESpt1PMayhOh5M=
 github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0 h1:DACJavvAHhabrF08vX0COfcOBJRhZ8lUbR+ZWIs0Y5g=
 github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0/go.mod h1:E/TSTwGwJL78qG/PmXZO1EjYhfJinVAhrmmHX6Z8B9k=
@@ -78,6 +82,8 @@ golang.org/x/exp v0.0.0-20190125153040-c74c464bbbf2/go.mod h1:CJ0aWSM057203Lf6IL
 golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20191002040644-a1355ae1e2c3 h1:n9HxLrNxWWtEb1cA950nuEEj3QnKbtsCJ6KjcgisNUs=
 golang.org/x/exp v0.0.0-20191002040644-a1355ae1e2c3/go.mod h1:NOZ3BPKG0ec/BKJQgnvsSFpcKLM5xXVWnvZS97DWHgE=
+golang.org/x/exp v0.0.0-20220613132600-b0d781184e0d h1:vtUKgx8dahOomfFzLREU8nSv25YHnTgLBn4rDnWZdU0=
+golang.org/x/exp v0.0.0-20220613132600-b0d781184e0d/go.mod h1:Kr81I6Kryrl9sr8s2FK3vxD90NdsKWRuOIl2O4CvYbA=
 golang.org/x/image v0.0.0-20180708004352-c73c2afc3b81/go.mod h1:ux5Hcp/YLpHSI86hEcLt0YII63i6oz57MZXIpbrjZUs=
 golang.org/x/image v0.0.0-20190227222117-0694c2d4d067/go.mod h1:kZ7UVZpmo3dzQBMxlp+ypCbDeSB+sBbTgSJuh5dn5js=
 golang.org/x/image v0.0.0-20190802002840-cff245a6509b/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
@@ -92,6 +98,8 @@ golang.org/x/image v0.0.0-20210628002857-a66eb6448b8d/go.mod h1:023OzeP/+EPmXeap
 golang.org/x/image v0.0.0-20211028202545-6944b10bf410/go.mod h1:023OzeP/+EPmXeapQh35lcL3II3LrY8Ic+EFFKVhULM=
 golang.org/x/image v0.0.0-20220302094943-723b81ca9867 h1:TcHcE0vrmgzNH1v3ppjcMGbhG5+9fMuvOmUYwNEF4q4=
 golang.org/x/image v0.0.0-20220302094943-723b81ca9867/go.mod h1:023OzeP/+EPmXeapQh35lcL3II3LrY8Ic+EFFKVhULM=
+golang.org/x/image v0.0.0-20220617043117-41969df76e82 h1:KpZB5pUSBvrHltNEdK/tw0xlPeD13M6M6aGP32gKqiw=
+golang.org/x/image v0.0.0-20220617043117-41969df76e82/go.mod h1:doUCurBvlfPMKfmIpRIywoHmhN3VyhnoFDbvIEWF4hY=
 golang.org/x/mobile v0.0.0-20190719004257-d2bd2a29d028/go.mod h1:E/iHnbuqvinMTCcRqshq8CkpyQDoeVncDDYHnLhea+o=
 golang.org/x/mod v0.1.0/go.mod h1:0QHyrYULN0/3qlju5TqG8bIK38QM8yzMo5ekMj3DlcY=
 golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
@@ -117,6 +125,7 @@ golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/text v0.3.5/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/text v0.3.7 h1:olpwvP2KacW1ZWvsR7uQhoyTYvKAupfQrRGBFM352Gk=
 golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
 golang.org/x/tools v0.0.0-20180525024113-a5b4c53f6e8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
@@ -125,6 +134,8 @@ golang.org/x/tools v0.0.0-20190927191325-030b2cf1153e/go.mod h1:b+2E5dAYhXwXZwtn
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.1.0/go.mod h1:xkSsbof2nBLbhDlRMhhhyNLN/zl3eTqcnHD5viDpcZ0=
 golang.org/x/tools v0.1.9/go.mod h1:nABZi5QlRsZVlzPpHl034qft6wpY4eDcsTt5AaioBiU=
+golang.org/x/tools v0.1.11 h1:loJ25fNOEhSXfHrpoGj91eCUThwdNX6u24rO1xnNteY=
+golang.org/x/tools v0.1.11/go.mod h1:SgwaegtQh8clINPpECJMqnxLv9I09HLqnW3RMqW0CA4=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
@@ -134,6 +145,8 @@ gonum.org/v1/gonum v0.8.2/go.mod h1:oe/vMfY3deqTw+1EZJhuvEW2iwGF1bW9wwu7XCu0+v0=
 gonum.org/v1/gonum v0.9.3/go.mod h1:TZumC3NeyVQskjXqmyWt4S3bINhy7B4eYwW69EbyX+0=
 gonum.org/v1/gonum v0.11.0 h1:f1IJhK4Km5tBJmaiJXtk/PkL4cdVX6J+tGiM187uT5E=
 gonum.org/v1/gonum v0.11.0/go.mod h1:fSG4YDCxxUZQJ7rKsQrj0gMOg00Il0Z96/qMA4bVQhA=
+gonum.org/v1/gonum v0.11.1-0.20220625074215-67f3e1dbfccc h1:ADX7LJ8SknE89dXBcPhZGGV60cMUzqB9XcaNKuHZxy4=
+gonum.org/v1/gonum v0.11.1-0.20220625074215-67f3e1dbfccc/go.mod h1:fSG4YDCxxUZQJ7rKsQrj0gMOg00Il0Z96/qMA4bVQhA=
 gonum.org/v1/netlib v0.0.0-20190313105609-8cb42192e0e0/go.mod h1:wa6Ws7BG/ESfp6dHfk7C6KdzKA7wR7u/rKwOGE66zvw=
 gonum.org/v1/plot v0.0.0-20190515093506-e2840ee46a6b/go.mod h1:Wt8AAjI+ypCyYX3nZBvf6cAIx93T+c/OS2HFAYskSZc=
 gonum.org/v1/plot v0.9.0/go.mod h1:3Pcqqmp6RHvJI72kgb8fThyUnav364FOsdDo2aGW5lY=
diff --git a/helpers/sdfexp/import.go b/helpers/sdfexp/import.go
index 0ec7630..10fcbc7 100644
--- a/helpers/sdfexp/import.go
+++ b/helpers/sdfexp/import.go
@@ -6,7 +6,6 @@ import (
 	"math"
 
 	"github.com/soypat/sdf/internal/d3"
-	"github.com/soypat/sdf/render"
 	"gonum.org/v1/gonum/spatial/kdtree"
 	"gonum.org/v1/gonum/spatial/r3"
 )
@@ -17,7 +16,7 @@ import (
 // using vertexTol.
 // vertexTol should be of the order of 1/1000th of the size of the smallest
 // triangle in the model. If set to 0 then it is inferred automatically.
-func ImportModel(model []render.Triangle3, vertexTolOrZero float64) (ImportedSDF3, error) {
+func ImportModel(model []r3.Triangle, vertexTolOrZero float64) (ImportedSDF3, error) {
 	m, err := newMesh(model, vertexTolOrZero)
 	if err != nil {
 		return ImportedSDF3{}, err
@@ -61,7 +60,7 @@ type pseudoVertex struct {
 	N r3.Vec // Vertex Normal
 }
 
-func newMesh(triangles []render.Triangle3, tol float64) (*mesh, error) {
+func newMesh(triangles []r3.Triangle, tol float64) (*mesh, error) {
 	bb := d3.Box{d3.Elem(math.MaxFloat64), d3.Elem(-math.MaxFloat64)}
 	minDist2 := math.MaxFloat64
 	maxDist2 := -math.MaxFloat64
@@ -102,7 +101,7 @@ func newMesh(triangles []render.Triangle3, tol float64) (*mesh, error) {
 	cache := make(map[[3]int64]int)
 	ri := 1 / tol
 	for i, tri := range triangles {
-		norm := tri.Normal()
+		norm := r3.Unit(tri.Normal())
 		Tform := canalisTransform(tri)
 		InvT := Tform.Inv()
 		sdfT := meshTriangle{
diff --git a/helpers/sdfexp/spatial3.go b/helpers/sdfexp/spatial3.go
index 4d70895..7882f5f 100644
--- a/helpers/sdfexp/spatial3.go
+++ b/helpers/sdfexp/spatial3.go
@@ -4,7 +4,6 @@ import (
 	"math"
 
 	"github.com/soypat/sdf/internal/d3"
-	"github.com/soypat/sdf/render"
 	"gonum.org/v1/gonum/spatial/kdtree"
 	"gonum.org/v1/gonum/spatial/r2"
 	"gonum.org/v1/gonum/spatial/r3"
@@ -83,8 +82,8 @@ func (t *meshTriangle) CopySign(p r3.Vec, dist float64) (signed float64) {
 	return math.Copysign(dist, signed)
 }
 
-func (t *meshTriangle) triangle() render.Triangle3 {
-	return render.Triangle3{
+func (t *meshTriangle) triangle() r3.Triangle {
+	return r3.Triangle{
 		t.m.vertices[t.Vertices[0]].V,
 		t.m.vertices[t.Vertices[1]].V,
 		t.m.vertices[t.Vertices[2]].V,
@@ -96,7 +95,7 @@ func (t *meshTriangle) triangle() render.Triangle3 {
 //  - the triangle's first edge (t_0,t_1) is on the X axis
 //  - the triangle's first vertex t_0 is at the origin
 //  - the triangle's last vertex t_2 is in the XY plane.
-func canalisTransform(t render.Triangle3) d3.Transform {
+func canalisTransform(t r3.Triangle) d3.Transform {
 	u2 := r3.Sub(t[1], t[0])
 	u3 := r3.Sub(t[2], t[0])
 
@@ -124,7 +123,7 @@ func lowerVec(v r3.Vec) r2.Vec {
 	return r2.Vec{X: v.X, Y: v.Y}
 }
 
-func centroid(t render.Triangle3) r3.Vec {
+func centroid(t r3.Triangle) r3.Vec {
 	return r3.Scale(1./3., r3.Add(r3.Add(t[0], t[1]), t[2]))
 }
 
diff --git a/render/3mf.go b/render/3mf.go
index 670dd45..feea79c 100644
--- a/render/3mf.go
+++ b/render/3mf.go
@@ -109,7 +109,7 @@ type mf3Triangle struct {
 	V3 int `xml:"v3,attr"`
 }
 
-func (m *model) AddObject(name string, src []Triangle3) error {
+func (m *model) AddObject(name string, src []r3.Triangle) error {
 	id := len(m.Resources.Objects) + 1
 	type vertexEntry struct {
 		idx   int
diff --git a/render/internal_test.go b/render/internal_test.go
index 69f1fd0..8eb90e1 100644
--- a/render/internal_test.go
+++ b/render/internal_test.go
@@ -60,7 +60,7 @@ func TestSTLWriteReadback(t *testing.T) {
 	mismatches := 0
 	for iface, expect := range input {
 		got := output[iface]
-		if got.Degenerate(1e-12) {
+		if got.IsDegenerate(1e-12) {
 			t.Fatalf("triangle degenerate: %+v", got)
 		}
 		for i := range expect {
@@ -78,10 +78,10 @@ func TestSTLWriteReadback(t *testing.T) {
 func TestOctreeMultithread(t *testing.T) {
 	oct := NewOctreeRenderer(must3.Sphere(20), 100)
 	oct.concurrent = 2
-	buf := make([]Triangle3, oct.concurrent*100)
+	buf := make([]r3.Triangle, oct.concurrent*100)
 	var err error
 	var nt int
-	var model []Triangle3
+	var model []r3.Triangle
 	for err == nil {
 		nt, err = oct.ReadTriangles(buf)
 		model = append(model, buf[:nt]...)
diff --git a/render/io.go b/render/io.go
index 27caf0a..57653ad 100644
--- a/render/io.go
+++ b/render/io.go
@@ -1,14 +1,18 @@
 package render
 
-import "io"
+import (
+	"io"
+
+	"gonum.org/v1/gonum/spatial/r3"
+)
 
 // RenderAll reads the full contents of a Renderer and returns the slice read.
 // It does not return error on io.EOF, like the io.RenderAll implementation.
-func RenderAll(r Renderer) ([]Triangle3, error) {
+func RenderAll(r Renderer) ([]r3.Triangle, error) {
 	var err error
 	var nt int
-	result := make([]Triangle3, 0, 1<<12)
-	buf := make([]Triangle3, 1024)
+	result := make([]r3.Triangle, 0, 1<<12)
+	buf := make([]r3.Triangle, 1024)
 	for {
 		nt, err = r.ReadTriangles(buf)
 		if err != nil {
@@ -22,21 +26,21 @@ func RenderAll(r Renderer) ([]Triangle3, error) {
 	return result, err
 }
 
-type triangle3Buffer struct {
-	buf []Triangle3
+type TriangleBuffer struct {
+	buf []r3.Triangle
 }
 
 // Read reads from this buffer.
-func (b *triangle3Buffer) Read(t []Triangle3) int {
+func (b *TriangleBuffer) Read(t []r3.Triangle) int {
 	n := copy(t, b.buf)
 	b.buf = b.buf[n:]
 	return n
 }
 
 // Write appends triangles to this buffer.
-func (b *triangle3Buffer) Write(t []Triangle3) int {
+func (b *TriangleBuffer) Write(t []r3.Triangle) int {
 	b.buf = append(b.buf, t...)
 	return len(t)
 }
 
-func (b *triangle3Buffer) Len() int { return len(b.buf) }
+func (b *TriangleBuffer) Len() int { return len(b.buf) }
diff --git a/render/kdrender_test.go b/render/kdrender_test.go
index e79f924..3fc1165 100644
--- a/render/kdrender_test.go
+++ b/render/kdrender_test.go
@@ -50,7 +50,7 @@ var (
 	_ kdtree.Bounder   = kdTriangles{}
 )
 
-func NewKDSDF(model []Triangle3) sdf.SDF3 {
+func NewKDSDF(model []r3.Triangle) sdf.SDF3 {
 	mykd := make(kdTriangles, len(model))
 	// var min, max r3.Vec
 	for i := range mykd {
@@ -93,7 +93,7 @@ func (s kdSDF) Evaluate(v r3.Vec) float64 {
 		return 0
 	}
 	pointDir := r3.Sub(v, closest)
-	n := triangle.Normal()
+	n := r3.Unit(triangle.Normal())
 	alpha := math.Acos(r3.Cos(n, pointDir))
 	return math.Copysign(minDist, math.Pi/2-alpha)
 }
@@ -120,7 +120,7 @@ func (s kdSDF) Bounds() r3.Box {
 
 type kdTriangles []kdTriangle
 
-type kdTriangle Triangle3
+type kdTriangle r3.Triangle
 
 func (k kdTriangles) Index(i int) kdtree.Comparable {
 	return k[i]
@@ -187,7 +187,7 @@ func (a kdTriangle) Bounds() *kdtree.Bounding {
 }
 
 func (a kdTriangle) Normal() r3.Vec {
-	v := Triangle3(a)
+	v := r3.Triangle(a)
 	return v.Normal()
 }
 
diff --git a/render/marchingcubes.go b/render/marchingcubes.go
index 3fe975b..c187565 100644
--- a/render/marchingcubes.go
+++ b/render/marchingcubes.go
@@ -12,7 +12,7 @@ const (
 	marchingCubesMaxTriangles = 5
 )
 
-func mcToTriangles(dst []Triangle3, p [8]r3.Vec, v [8]float64, x float64) (n int) {
+func mcToTriangles(dst []r3.Triangle, p [8]r3.Vec, v [8]float64, x float64) (n int) {
 	if len(dst) < marchingCubesMaxTriangles {
 		panic("destination triangle buffer must be greater than 5")
 	}
@@ -41,12 +41,12 @@ func mcToTriangles(dst []Triangle3, p [8]r3.Vec, v [8]float64, x float64) (n int
 	table := mcTriangleTable[index]
 	count := len(table) / 3 // max count is 5, a.k.a marchingCubesMaxTriangles
 	for i := 0; i < count; i++ {
-		t := Triangle3{
+		t := r3.Triangle{
 			points[table[i*3+2]],
 			points[table[i*3+1]],
 			points[table[i*3+0]],
 		}
-		if !t.Degenerate(1e-12) {
+		if !t.IsDegenerate(1e-12) {
 			dst[n] = t
 			n++
 		}
diff --git a/render/octree_renderer.go b/render/octree_renderer.go
index c136c17..eea2b56 100644
--- a/render/octree_renderer.go
+++ b/render/octree_renderer.go
@@ -15,7 +15,7 @@ type octree struct {
 	dc        dc3
 	mu        sync.Mutex
 	todo      []cube
-	unwritten triangle3Buffer
+	unwritten TriangleBuffer
 	// concurrent goroutine processing.
 	concurrent int
 	// Number of triangles generated.
@@ -61,7 +61,7 @@ func NewOctreeRenderer(s sdf.SDF3, meshCells int) *octree {
 	cubes[0] = cube{sdf.V3i{0, 0, 0}, levels - 1} // process the octree, start at the top level
 	return &octree{
 		dc:        *newDc3(s, bb.Min, resolution, levels),
-		unwritten: triangle3Buffer{buf: make([]Triangle3, 0, 1024)},
+		unwritten: TriangleBuffer{buf: make([]r3.Triangle, 0, 1024)},
 		todo:      cubes,
 		cubes:     1,
 	}
@@ -69,7 +69,7 @@ func NewOctreeRenderer(s sdf.SDF3, meshCells int) *octree {
 
 // ReadTriangles writes triangles rendered from the model into the argument buffer.
 // returns number of triangles written and an error if present.
-func (oc *octree) ReadTriangles(dst []Triangle3) (n int, err error) {
+func (oc *octree) ReadTriangles(dst []r3.Triangle) (n int, err error) {
 	if len(dst) == 0 {
 		panic("cannot write to empty triangle slice")
 	}
@@ -104,7 +104,7 @@ func (oc *octree) ReadTriangles(dst []Triangle3) (n int, err error) {
 // Returned newCubes are non-empty cubes that should be processed in future calls to readTriangles.
 // Triangles that were not succesfully written to dst are stored in octree unwritten buffer.
 // This function is safe to call concurrently.
-func (oc *octree) readTriangles(dst []Triangle3, todo []cube) (n, cubesProcessed int, newCubes []cube) {
+func (oc *octree) readTriangles(dst []r3.Triangle, todo []cube) (n, cubesProcessed int, newCubes []cube) {
 	for _, cube := range todo {
 		if n == len(dst) {
 			// Finished writing all the buffer
@@ -112,7 +112,7 @@ func (oc *octree) readTriangles(dst []Triangle3, todo []cube) (n, cubesProcessed
 		}
 		if n+marchingCubesMaxTriangles > len(dst) {
 			// Not enough room in buffer to write all triangles that could be found by marching cubes.
-			tmp := make([]Triangle3, marchingCubesMaxTriangles)
+			tmp := make([]r3.Triangle, marchingCubesMaxTriangles)
 			tri, cubes := oc.processCube(tmp, cube)
 			oc.mu.Lock()
 			oc.unwritten.Write(tmp[:tri])
@@ -131,10 +131,10 @@ func (oc *octree) readTriangles(dst []Triangle3, todo []cube) (n, cubesProcessed
 
 // readTrianglesThreaded is a multithreaded triangle reader implementation for octree.
 // It writes nt triangles into dst.
-func (oc *octree) readTrianglesThreaded(dst []Triangle3) (nt int) {
+func (oc *octree) readTrianglesThreaded(dst []r3.Triangle) (nt int) {
 	var wg sync.WaitGroup
 	div := len(dst) / oc.concurrent
-	work := make([][]Triangle3, oc.concurrent)
+	work := make([][]r3.Triangle, oc.concurrent)
 	cubeWork := make([][]cube, oc.concurrent)
 	newCubesC := make([][]cube, oc.concurrent)
 	divC := len(oc.todo) / oc.concurrent
@@ -183,7 +183,7 @@ func (oc *octree) readTrianglesThreaded(dst []Triangle3) (nt int) {
 
 // Process a cube. Generate triangles, or more cubes.
 // Safe to call concurrently.
-func (oc *octree) processCube(dst []Triangle3, c cube) (writtenTriangles int, newCubes []cube) {
+func (oc *octree) processCube(dst []r3.Triangle, c cube) (writtenTriangles int, newCubes []cube) {
 	if c.n == 1 {
 		// this cube is at the required resolution
 		c0, d0 := oc.dc.Evaluate(c.Add(sdf.V3i{0, 0, 0}))
diff --git a/render/render.go b/render/render.go
index 594ad54..90c832b 100644
--- a/render/render.go
+++ b/render/render.go
@@ -1,34 +1,9 @@
 package render
 
 import (
-	"github.com/soypat/sdf/internal/d3"
-	"gonum.org/v1/gonum/spatial/r2"
 	"gonum.org/v1/gonum/spatial/r3"
 )
 
 type Renderer interface {
-	ReadTriangles(t []Triangle3) (int, error)
-}
-
-// Triangle2 is a 2D triangle
-type Triangle2 [3]r2.Vec
-
-// Triangle3 is a 3D triangle
-type Triangle3 [3]r3.Vec
-
-// Normal returns the normal vector to the plane defined by the 3D triangle.
-func (t *Triangle3) Normal() r3.Vec {
-	e1 := t[1].Sub(t[0])
-	e2 := t[2].Sub(t[0])
-
-	return r3.Unit(r3.Cross(e1, e2))
-}
-
-// Degenerate returns true if the triangle is degenerate.
-func (t *Triangle3) Degenerate(tolerance float64) bool {
-	// check for identical vertices.
-	// TODO more tests needed.
-	return d3.EqualWithin(t[0], t[1], tolerance) ||
-		d3.EqualWithin(t[1], t[2], tolerance) ||
-		d3.EqualWithin(t[2], t[0], tolerance)
+	ReadTriangles(t []r3.Triangle) (int, error)
 }
diff --git a/render/render_test.go b/render/render_test.go
index 0ba87e4..1027a34 100644
--- a/render/render_test.go
+++ b/render/render_test.go
@@ -1,6 +1,7 @@
 package render_test
 
 import (
+	"math/rand"
 	"os"
 	"runtime/pprof"
 	"testing"
@@ -10,6 +11,7 @@ import (
 	"github.com/soypat/sdf/form3/obj3/thread"
 	"github.com/soypat/sdf/internal/d3"
 	"github.com/soypat/sdf/render"
+	"gonum.org/v1/gonum/spatial/r2"
 	"gonum.org/v1/gonum/spatial/r3"
 )
 
@@ -92,3 +94,54 @@ func startProf(t testing.TB, name string) {
 		t.Fatal(err)
 	}
 }
+
+func TestTriangle(t *testing.T) {
+	const tol = 1e-12
+	rng := rand.New(rand.NewSource(1))
+	for i := 0; i < 100; i++ {
+		tri := randTriangle(rng)
+		golden := Triangle3{}
+		for j := range tri {
+			golden[j] = tri[j]
+		}
+		got := tri.Normal()
+		expect := golden.Normal()
+		if !d3.EqualWithin(got, expect, tol) {
+			t.Errorf("expect %f, got %f", expect, got)
+		}
+	}
+}
+
+func randVec(rng *rand.Rand) r3.Vec {
+	return r3.Vec{X: 20 * (rng.Float64() - .5), Y: 20 * (rng.Float64() - .5), Z: 20 * (rng.Float64() - .5)}
+}
+
+func randTriangle(rng *rand.Rand) r3.Triangle {
+	return r3.Triangle{
+		randVec(rng),
+		randVec(rng),
+		randVec(rng),
+	}
+}
+
+// Triangle2 is a 2D triangle
+type Triangle2 [3]r2.Vec
+
+// Triangle3 is a 3D triangle
+type Triangle3 [3]r3.Vec
+
+// Normal returns the normal vector to the plane defined by the 3D triangle.
+func (t *Triangle3) Normal() r3.Vec {
+	e1 := t[1].Sub(t[0])
+	e2 := t[2].Sub(t[0])
+	return r3.Cross(e1, e2)
+}
+
+// Degenerate returns true if the triangle is degenerate.
+func (t *Triangle3) Degenerate(tolerance float64) bool {
+	// check for identical vertices.
+	// TODO more tests needed.
+	return d3.EqualWithin(t[0], t[1], tolerance) ||
+		d3.EqualWithin(t[1], t[2], tolerance) ||
+		d3.EqualWithin(t[2], t[0], tolerance)
+}
diff --git a/render/stl.go b/render/stl.go
index da4eefb..949f760 100644
--- a/render/stl.go
+++ b/render/stl.go
@@ -19,7 +19,7 @@ func CreateSTL(path string, r Renderer) error {
 }
 
 // WriteSTL writes model triangles to a writer in STL file format.
-func WriteSTL(w io.Writer, model []Triangle3) error {
+func WriteSTL(w io.Writer, model []r3.Triangle) error {
 	if len(model) == 0 {
 		return errors.New("empty triangle slice")
 	}
@@ -43,7 +43,7 @@ func WriteSTL(w io.Writer, model []Triangle3) error {
 	var d stlTriangle
 	for _, triangle := range model {
 		var b [50]byte
-		n := triangle.Normal()
+		n := r3.Unit(triangle.Normal())
 		d.Normal[0] = float32(n.X)
 		d.Normal[1] = float32(n.Y)
 		d.Normal[2] = float32(n.Z)
@@ -80,7 +80,7 @@ const trianglesInBuffer = 1 << 14
 
 type stlReader struct {
 	r   Renderer
-	buf [trianglesInBuffer]Triangle3
+	buf [trianglesInBuffer]r3.Triangle
 }
 
 func (w *stlReader) Read(b []byte) (int, error) {
@@ -109,7 +109,7 @@ func (w *stlReader) Read(b []byte) (int, error) {
 			panic("bug: buffer overflow")
 		}
 		for _, triangle := range w.buf[:nt] {
-			n := triangle.Normal()
+			n := r3.Unit(triangle.Normal())
 			d.Normal[0] = float32(n.X)
 			d.Normal[1] = float32(n.Y)
 			d.Normal[2] = float32(n.Z)
@@ -169,7 +169,7 @@ func min(a, b int) int {
 	return b
 }
 
-func readBinarySTL(r io.Reader) (output []Triangle3, readErr error) {
+func readBinarySTL(r io.Reader) (output []r3.Triangle, readErr error) {
 	var header stlHeader
 	if err := binary.Read(r, binary.LittleEndian, &header); err != nil {
 		if errors.Is(err, io.ErrUnexpectedEOF) {
@@ -213,7 +213,7 @@ func readBinarySTL(r io.Reader) (output []Triangle3, readErr error) {
 				return nil, err
 			}
 		}
-		output = append(output, d.toTriangle3())
+		output = append(output, d.Triangle())
 	}
 	// NormalMismatch error validation may be returned.
 	// For high resolution models this error may be incorrectly returned.
@@ -324,8 +324,8 @@ func equalWithin3F32(a, b [3]float32, tol float32) bool {
 		math32.Abs(a[2]-b[2]) <= tol
 }
 
-func (d stlTriangle) toTriangle3() Triangle3 {
-	return Triangle3{
+func (d stlTriangle) Triangle() r3.Triangle {
+	return r3.Triangle{
 		r3From3F32(d.Vertex1),
 		r3From3F32(d.Vertex2),
 		r3From3F32(d.Vertex3),