Terrain visibility analysis

Can you see Mont Blanc from Mont Aigoual?

Short answer: Yes, theoretically, from this exact mapped summit point on Mont Aigoual. Mont Blanc clears the modelled terrain horizon over 321.3 km, with high model confidence and a summit margin of about +400 m. Clear air and suitable atmospheric conditions remain essential; this is not a guaranteed sighting or a verdict for the entire massif.

Mont Blanc from the mapped Mont Aigoual summit point: a 321.3 km terrain profile with standard refraction, exact coordinates and atmospheric limits.

View the calculation in Sightelo

Key figures

Observation point: Mapped Mont Aigoual summit point, at ground level, France; Latitude, longitude: 44.1216253, 3.5813643; Modelled ground elevation: 1549.1 m; Eye height: 1.7 m
Point of interest: Mont Blanc, catalogue summit reference, France and Italy
Target elevation: 4,807.3 m
Straight-line distance: 321.3 km
Direction to the summit: 52.6° (northeast)
Modelled summit clearance: +400 m

Terrain profile and line of sight

Detailed profile

Scroll horizontally to explore the full profile on a small screen.

Calculated terrain
Observer–summit sight line
Minimum visibility line
Elevation reference: 0 m

Terrain already includes modelled curvature and refraction (k = 0.13). The grey curve projects a constant elevation of 0 m using that model; it is not an observed sea level. Subtract it from the terrain curve to read elevation. Sight lines remain straight; no second curvature correction is applied. Vertical and horizontal scales differ.

At the summit, the target clears the modelled horizon by 400.5 m. No blocking terrain is calculated. The relief forming the horizon is 198.688 km from A.

The calculation models terrain, Earth curvature and standard atmospheric refraction. It does not model buildings, trees, clouds, haze or local atmospheric variations.

Calculated profile values

Distance (km)	321.3 km
Observer eye altitude	1550.8 m
Summit altitude	4807.3 m
Minimum visible target altitude	4406.8 m
Target margin above the modelled horizon	+400.5 m
Minimum local sight-line clearance	+45.7 m
Displayed / calculated samples	499 / 3214
Excluded around A / B	200 m / 1400 m
Horizon-forming relief	198.6881 km

Audited calculation: 2026-10-22. The interactive calculator can recalculate with currently available elevation data.

What this example helps you study

This calculation starts at the mapped Mont Aigoual peak (OSM node 26863762), at ground level, not on the observatory tower or its orientation table. Copernicus gives a surface elevation of 1,549.1 m at this point; the mapped peak height and the tourist summit height are different references and do not replace the DEM. Mont Blanc uses the catalogue reference of 4,807.3 m. The modelled horizon is formed about 198.7 km away. A +400 m summit margin differs from the minimum local clearance of about 46 m. Over 321.3 km, actual refraction, haze, cloud and contrast strongly limit observation; high model confidence is not a weather forecast. No ridge name or blocking obstacle is inferred. This result applies only to the studied point, not the whole Aigoual massif.

Limits of interpretation

The calculation models terrain, Earth curvature and standard atmospheric refraction. It does not model buildings, trees, clouds, haze or local atmospheric variations.

Technical details

Observation point coordinates: 44.1216253, 3.5813643
Summit coordinates: 45.832706, 6.865171
Terrain model: Copernicus DEM 90
Eye height: 1.7 m
Refraction used: Standard (k = 0.13)
Sample step: 100 m
Uncertainty threshold: 30 m
Observer exclusion radius: 200 m
Requested summit exclusion radius: 600 m

A positive value means the summit clears the modelled terrain horizon. A negative value means the summit lies below the minimum elevation required to clear that horizon. This value is not the local height of blocking terrain above the sight line.