go-rtk

Go package wrapping RTKLIB via CGo for PPK (Post-Processed Kinematic) GNSS post-processing. Works with drone image metadata, RINEX observation files, .pos solutions, and .MRK timestamp files.

Package

import "github.com/flywave/go-rtk"

Single flat package rtk — no sub-packages.

Dependencies

Dependency	Source
RTKLIB (C)	external/rtklib/ — prebuilt as lib/librtklib.a
go-proj	coordinate transforms via PROJ
go-geoid	EGM84/96/2008 geoid height conversions
goexif	EXIF tag parsing
go-xmp	XMP metadata parsing
gocsv	CSV marshaling for .MRK files

go-proj and go-geoid are local replaces in go.mod — they must exist as siblings at ../go-proj and ../go-geoid.

Build

go build ./...
go test ./...
go vet ./...

lib/librtklib.a is checked in. To rebuild from source: cmake external/rtklib && make.

Usage

PPK processing

poses, trange := rtk.ReadPos("solution.pos")
mrks, err := rtk.ReadMRK(mrkFile)

rtk.PPKInitPos(poses, mrks)
rtk.PPKUpdatedMrks(mrks)

sols, err := rtk.PPKSolution("solution.pos", "marks.MRK",
    rtk.WGS84, rtk.HAE, "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs",
    rtk.HAE, 0.0)

GNSS time handling

gt := rtk.NewGTimeFromGPSTime(2024, 275295.301059)
week, sec := gt.GpsTime()
ep := gt.Epoch()      // [year, month, day, hour, min, sec]
utc := gt.UTC()
diff := gt.Diff(otherGT)
gt.Add(30.0)           // add seconds

EXIF / XMP metadata

f, _ := os.Open("image.jpg")
err, fields := rtk.ReadExifXMP(f)
// fields["drone-dji: RtkFlag"], fields["drone-dji: RtkStdLon"], etc.

Coordinate transforms

h := rtk.MSLToWGS84(100.0, 120.0, 30.0, geoid.EGM2008)
h = rtk.WGS84ToMSL(120.0, 30.0, 100.0, geoid.EGM96)
h = rtk.HAEToMSL(120.0, 30.0, 100.0, 0.0, geoid.EGM84)

Solution processing (RINEX → .pos)

err := rtk.Solution("rover.obs", "base.obs", "brdc.nav", "output.pos")

File formats

Format	Reader	Description
.pos	ReadPos	RTKLIB solution file (tab-separated, header lines start with %)
.MRK	ReadMRK	Tab-separated timestamp marks with GPS week/SOW, phase center offsets, and RTK state
.exif / XMP	ReadExifXMP	DJI drone image metadata (RtkFlag, RtkStd, absolute altitude)
.obs / .nav	Solution	RINEX observation and navigation files (via RTKLIB)
.bin	RawToRIndex	RTCM3 binary → RINEX conversion

.MRK columns

Sequence  GPSSecondOfWeek  GPSWeek  NorthOff  EastOff  VelOff  Latitude  Longitude  EllipsoidHeight  Std  RtkState

Tab-delimited, no header row.

Data directories

• proj_data/ — PROJ datum grids and transform files
• geoid_data/ — EGM84/96/2008 geoid height grids (PGM format)
• testdata/ — sample .pos, .MRK, .exif, and RINEX files for testing

Paths are set automatically via init() — no environment variables needed.

Notes

• Go 1.13 compatible (no generics, no errors.Is/errors.As, no os.ReadFile)
• CGo with per-file #cgo directives in gtime.go, pos.go, solution.go, ppkraw.go
• Tests use t.FailNow() on failure (no error messages)
• go.sum has no entries for replace-only deps — CI may need -mod=mod