GNSS Tools¶

A collection of browser-based tools for GNSS, RTK, and coordinate work.

Coordinate Converter¶

Converts between common geodetic and projected coordinate reference systems used in Denmark and Europe.
Please note that the calculations might differ in the final decimal place. Different tools use different rounding method, we are using the PROJ conversions here.

From CRS

To CRS

Easting (m)

Northing (m)

Height (m, optional)

Decimal Degrees ↔ DMS¶

Latitude

Longitude

For DMS input use any common format: 55°40'34.03"N, 55 40 34.03 N, or 55 40 34.03.

Distance & Bearing¶

Geodetic distance and bearing between two WGS84 points (Vincenty formula, accuracy ±0.5 mm).

Point A

Point B

NTRIP Caster Tester¶

Generates curl commands ready to run from a terminal. Browsers can't connect to most NTRIP casters directly (CORS + HTTP/0.9), so this is the practical alternative.

For RTCM stream capture, the generated command pipes the output through xxd to produce hex — paste that hex straight into the RTCM Message Analyzer below.

NTRIP 1.0 casters respond with SOURCETABLE 200 OK instead of a standard HTTP status line, which curl rejects by default. The --http0.9 flag in the generated commands handles this.

Host / IP

Port

Username (optional)

Password (optional)

Mountpoint (optional — leave blank to fetch source table only)

RTCM Message Analyzer¶

Paste an RTCM 3.x stream as a hex string (or base64) to see which message types it contains. Useful when diagnosing what correction data a base station or NTRIP caster is actually sending — and whether it matches what your rover expects.

Capture RTCM bytes from a serial log, str2str, Wireshark, or your GNSS receiver's debug output and paste the hex dump here.

RTCM hex or base64 input

NMEA Sentence Parser¶

Paste one or more NMEA sentences to decode them. Supports GGA, RMC, GSA, GLL, VTG, GSV.

NMEA input

RTK Base Station Correction¶

When your RTK base is placed at an assumed or approximate position, all rover measurements carry that same offset error.

How it works: Measure a known survey point with your rover.
Enter the base current configured assumed position, the true survey point coordinates, and your rover measurement of that survey point.
The tool calculates the position offset and outputs corrected base coordinates. Enter those into your base, and all future rover measurements should be accurate.

Base — current assumed coordinates Lat Lon [Height] — space-separated, WGS84 decimal degrees

Survey point — true/official coordinates Lat Lon [Height] — from official source

Survey point — rover measurement with RTK corrections from your base Lat Lon [Height] — what your rover actually measured at the survey point

I only made 1 of the tools on here, then figured out LLM was faster anyway if we ignore the disagreements that took hours.