GNSS Engineering Tools
WGS84 Baseline Distance Calculator
Enter two lat/lon points and get the geodesic distance, initial and final bearings, 3D chord through the Earth, and great-circle midpoint — accurate to sub-millimetre using Vincenty's inverse formula on the WGS84 ellipsoid. Built for RTK base-rover separation planning, CORS network design, monitoring-network layouts, and antenna direction-finding spacing.
Two points, one ellipsoidal baseline
Edit any latitude or longitude and the distance and bearings recompute live. Pick a preset to start from a known baseline, or share the page URL — it stays in sync so a colleague gets exactly the same numbers when they open the link.
Point A (origin)
Point B (destination)
Geodesic distance
1936.8 km
Vincenty's inverse on WGS84 ellipsoid
Initial bearing (A → B)
6.40°
N
Final bearing (arrive at B)
7.70°
N
3D chord
1929.3 km
Straight-line ECEF distance through Earth's interior
Height difference
+20.00 m
Δh (B − A)
Great-circle midpoint
31.2422, 115.0393
Vincenty's inverse formula: Distance is computed on the WGS84 ellipsoid. Vincenty's algorithm converges to sub-millimetre for all baselines except near-antipodal pairs (when A and B are within ~0.5° of opposite sides of the planet), where the spherical haversine is used as a stable fallback — accurate to ~0.5% in that edge case.
What this is for
What this is for
Geodesic baseline distance shows up in every GNSS deployment plan. Each scenario below uses exactly the same Vincenty computation — the differences are what the numbers mean in context.
RTK base-rover planning
Multi-frequency RTK fixes degrade roughly 1 ppm per km of baseline length under good ionospheric conditions, and faster on long baselines or active geomagnetic days. Use this calculator to verify the base-to-rover separation is inside your accuracy budget before deploying.
CORS network layout
Continuously operating reference stations are typically spaced 50–100 km for regional RTK networks, 200–300 km for national CORS coverage. Check inter-station distances before submitting a network design to a survey authority.
Deformation monitoring
Long-term ground motion is measured as changes in the baseline vector between monuments. The geodesic distance + 3D chord here gives you the reference epoch length to compare against.
Direction-finding & TDOA spacing
Multi-antenna direction-finding (and time-difference-of-arrival ranging) requires precise inter-element baselines and known bearings. The initial/final bearing outputs feed straight into TDOA geometry calculations.
Site-to-site mission planning
Aviation, UAV, and survey-team mission planning all need cross-site distance and azimuth. Drop a preset for a known reference pair, or paste coordinates from your flight plan to verify range.
Sanity check Vincenty vs. spherical
If your existing pipeline uses haversine and you're seeing ~10 km errors over transcontinental distances, this is why — haversine on a sphere is ~0.3% off from ellipsoidal geodesic. The 3D chord here also lets you see the centimetre-level surface-vs-chord gap for short baselines.
FAQ
Frequently asked questions
Common questions about geodesic baseline computation and how this calculator handles the edge cases.
Why does my distance differ from Google Maps or a flight-tracker site?
Most consumer maps use spherical haversine on Earth's mean radius — that's about 0.3% off (~15–20 km on transcontinental routes) vs the true ellipsoidal geodesic. Aviation flight planners often add a great-circle adjustment for cruise altitude. This calculator returns the WGS84-ellipsoid geodesic, which is what GNSS receivers and post-processors actually use.
What's the difference between geodesic distance and 3D chord?
Geodesic distance is along the curved surface of the WGS84 ellipsoid. The 3D chord is the straight line through Earth's interior, computed by converting both points to ECEF XYZ. For a 100 km baseline the difference is about 60 cm. For a 1000 km baseline it's about 65 m. For interferometric baseline calculations you usually want the 3D chord; for distance-on-ground you want the geodesic.
How accurate is Vincenty's inverse formula?
Sub-millimetre for any baseline outside the near-antipodal region (when the two points are within roughly 0.5° of opposite sides of the planet). For antipodal pairs the iteration oscillates and never converges — this calculator falls back to the spherical haversine, accurate to ~0.5% in that degenerate case. The fallback is signalled in the method footnote under the results.
Why are the initial and final bearings different?
On a curved Earth a constant heading does not follow a great-circle (that's a rhumb line / loxodrome — longer than the geodesic). The great-circle has changing bearing along the path. Initial bearing is your heading at A; final bearing is your heading when you arrive at B. For short baselines they're nearly identical; for transcontinental routes they can differ by tens of degrees.
Can I share my computed baseline with a colleague?
Yes — every edit updates the page URL with the two coordinate pairs as query parameters. Copy the address bar and send the link. Opening it on any browser drops both pins at the same locations and reproduces the same distance and bearings.
Does this account for ellipsoidal vs orthometric height?
The horizontal distance and bearings are independent of height. The Δh result is the raw difference between the two altitudes you enter — whatever frame you provided them in. If both altitudes are ellipsoidal (WGS84) Δh is the ellipsoidal height difference. If both are orthometric (mean sea level / EGM2008), Δh is the orthometric height difference. Don't mix the two.
Need RTK-grade antennas for long baselines?
Sub-mm geodesic computation is only useful if the antennas at both ends actually deliver that accuracy. Browse our high-precision 3D choke ring, multi-frequency survey, and CORS-grade product lines, or send your network layout and we'll spec a fit.