Overlap over high terrain

A mission flown at one height above takeoff is closer to the ground over hills, so photos cover less and overlap drops. The lowest overlap and the height left over the highest ground.

Planning and education aid. Not for primary navigation. Full disclaimer

A published result changed on 2026-09-23: Promoting this tool to stable removed EXPERIMENTAL_TOOL from its warnings, which moved OVERLAP_BELOW_TARGET from index 1 to index 0 and broke eight vectors that pinned the index. Nothing computed changed. v001, v003, v004, v005, v007, v010, v011, and v012 are superseded by v015 to v022, which name the warning with the meta.warnings.*.code form. Changelog

Computing your own values needs JavaScript and WebAssembly. The worked example below was computed when this page was built, and the documentation under "How we got this" applies.

60m

Over the highest ground the drone is 60 m up, and front overlap drops to 58.3 percent.

Caution:Front overlap falls to 58.3% over the highest ground, under 75%; side overlap falls to 41.7% over the highest ground, under 65%.

Front overlap there
Side overlap there

Provenance

Computed by: drone.photogrammetry.terrain-overlap 1.0.0, core 0.1.0
Model: The footprint scales with height above the ground, h − t, while photo and line spacing stay fixed from the flat plan at h. Overlap there = 1 − (1 − o)·h/(h − t); GSD = pixel pitch × (h − t)/f. The height that keeps overlap o_min at the terrain solves (1 − o)·h/(h − t) = 1 − o_min for h, with spacing replanned at that height (Wolf, Dewitt & Wilkinson 2014, ch. 18)
Accuracy: Exact for a vertical camera over the stated highest ground; use the highest point along any flight line, and a DEM profile for more
Notes: 1 shown with the answer
Cites: Wolf, P. R., Dewitt, B. A., and Wilkinson, B. E., McGraw-Hill, Elements of Photogrammetry with Applications in GIS; Pryor, W. T., Bureau of Public Roads, Highway Research Board Bulletin 228, Relationship of Topographic Relief, Flight Height, and Minimum and Maximum Overlap

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Your values

Showing an example. Change anything.

Height above takeoff The mission's flight height, like 100 m · plain numbers mean m Highest ground Its height above the takeoff point, like 40 m · plain numbers mean m Planned front overlap Percent over flat ground, like 75 Planned side overlapoptional Percent over flat ground, like 65

More options 4

Lowest overlap you acceptoptional Percent, like 70; the planned overlap if left out Sensor widthoptional For the GSD, like 13.2 mm · plain numbers mean mm Focal lengthoptional For the GSD, like 8.8 mm · plain numbers mean mm Image widthoptional For the GSD: pixels across, like 5472

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How we got thisFormula, worked example, sources, and proof

Model: The footprint scales with height above the ground, h − t, while photo and line spacing stay fixed from the flat plan at h. Overlap there = 1 − (1 − o)·h/(h − t); GSD = pixel pitch × (h − t)/f. The height that keeps overlap o_min at the terrain solves (1 − o)·h/(h − t) = 1 − o_min for h, with spacing replanned at that height (Wolf, Dewitt & Wilkinson 2014, ch. 18)

Accuracy: Exact for a vertical camera over the stated highest ground; use the highest point along any flight line, and a DEM profile for more

When to use this: Use this before you fly a mapping mission over hills at one height above the takeoff point. It shows how much front and side overlap is left over the highest ground, and the height to fly instead so the overlap there stays at the lowest value your processing software accepts.

Limitations: It checks one highest point, not a full terrain profile, and assumes a camera pointing straight down. Trees and buildings on the high ground bring the surface even closer. Flying higher to hold overlap also coarsens the GSD over low ground, and the new height must still fit your altitude limit. A terrain-following flight avoids the problem instead.

Worked example: 100 m above takeoff over a 40 m hill at 75/65 overlap. Source: add-drone-suite hill scenario. It is golden test vector v015, and every build checks the tool still gives its answer within its tolerance.

You enter

Planned front overlap: 75
Height above takeoff: 100 m
Highest ground: 40 m
Planned side overlap: 65

You get

Height over the highest ground: 60 m
Front overlap there: 58.3
Side overlap there: 41.7

Review: Not yet independently reviewed by a Part 107 remote pilot.

Last verified: 2026-09-18, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.0.0, core 0.1.0. See this tool in the verification report.

Changes

2026-09-23, result change: Promoting this tool to stable removed EXPERIMENTAL_TOOL from its warnings, which moved OVERLAP_BELOW_TARGET from index 1 to index 0 and broke eight vectors that pinned the index. Nothing computed changed. v001, v003, v004, v005, v007, v010, v011, and v012 are superseded by v015 to v022, which name the warning with the meta.warnings.*.code form. Changelog

Checked against: 21 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

Elements of Photogrammetry with Applications in GIS, Wolf, P. R., Dewitt, B. A., and Wilkinson, B. E., McGraw-Hill, 4th edition. Chapter 18 (flight planning: effect of terrain on overlap). Read free.
Relationship of Topographic Relief, Flight Height, and Minimum and Maximum Overlap, Pryor, W. T., Bureau of Public Roads, Highway Research Board Bulletin 228, Bulletin 228. pp. 31 and 36-37 (endlap at the datum and at the point of highest relief).

Terms

GSD: ground sampling distance: The ground width one image pixel covers, such as 2 cm per pixel. A smaller GSD shows more detail. Source: Elements of Photogrammetry with Applications in GIS

Learn the concept: Photo overlap and flight lines explained