COLMAP Points3D Binary format

README.md

@@ -2,6 +2,33 @@
 
 Structs for interacting with reconstruction data from different SFM programs
 
+## COLMAP
+
+Interact with COLMAPS's `points3D.bin` file output under the sparse reconstruction data.
+
+
+```golang
+package example
+
+import (
+	"fmt"
+
+	"github.com/EliCDavis/sfm/colmap"
+)
+
+func main() {
+	points, err := colmap.ReadPoints3D("ColmapProject/sparse/0/points3D.bin")
+
+	if err != nil {
+		panic(err)
+	}
+
+
+	fmt.Printf("File contains %d points", len(points))
+}
+
+```
+
 ## Meshroom
 
 Interact with Meshroom's `cameras.sfm` file output from the `StructureFromMotion` step.

colmap/points.go

@@ -0,0 +1,73 @@
+package colmap
+
+import (
+	"encoding/binary"
+	"image/color"
+	"os"
+
+	"github.com/EliCDavis/bitlib"
+	"github.com/EliCDavis/vector/vector3"
+)
+
+// Everything transcribed from
+// https://github.com/colmap/colmap/blob/main/scripts/python/read_write_model.py
+// https://docs.python.org/3/library/struct.html
+
+type Point3DTrack struct {
+	ImageID   int
+	Point2DID int
+}
+
+type Point3D struct {
+	ID       uint64
+	Position vector3.Float64
+	Color    color.RGBA
+	Error    float64
+	Tracks   []Point3DTrack // as (IMAGE_ID, POINT2D_IDX)
+}
+
+func ReadPoints3DBinary(filename string) ([]Point3D, error) {
+	f, err := os.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	reader := bitlib.NewReader(f, binary.LittleEndian)
+
+	numPoints := reader.UInt64()
+	points := make([]Point3D, numPoints)
+
+	for i := uint64(0); i < numPoints; i++ {
+		p := Point3D{}
+
+		p.ID = reader.UInt64()
+
+		p.Position = vector3.New(
+			reader.Float64(),
+			reader.Float64(),
+			reader.Float64(),
+		)
+
+		c := color.RGBA{A: 255}
+		c.R = reader.Byte()
+		c.G = reader.Byte()
+		c.B = reader.Byte()
+		p.Color = c
+
+		p.Error = reader.Float64()
+
+		numTracks := reader.UInt64()
+		p.Tracks = make([]Point3DTrack, numTracks)
+		for trackIndex := uint64(0); trackIndex < numTracks; trackIndex++ {
+			track := Point3DTrack{}
+			track.ImageID = int(reader.Int32())
+			track.Point2DID = int(reader.Int32())
+			p.Tracks[trackIndex] = track
+		}
+
+		points[i] = p
+	}
+
+	return points, reader.Error()
+}

go.mod

@@ -1,3 +1,8 @@
 module github.com/EliCDavis/sfm
 
 go 1.21.0
+
+require (
+	github.com/EliCDavis/bitlib v1.0.0
+	github.com/EliCDavis/vector v1.5.0
+)

go.sum

@@ -0,0 +1,4 @@
+github.com/EliCDavis/bitlib v1.0.0 h1:iMWUThiBzXnEQTAG3C5Mtjzfna8cpFhrmQylhWSJINM=
+github.com/EliCDavis/bitlib v1.0.0/go.mod h1:B/mBEBsbOKSL85ELpHDmN1ncf1gO14Nrum184HWHcPQ=
+github.com/EliCDavis/vector v1.5.0 h1:IE7Xco/V9S0inlIoIPu5J87Nnup9RJUEK/PiDLsueY8=
+github.com/EliCDavis/vector v1.5.0/go.mod h1:A+Zf8tDKfocwQa9md33HsE53KclL7uayR/cKjKHUFSA=