Flight planning

Overlap: how much two photos share.

To turn photos into a model, every point has to appear in several images. The overlap decides how many. 80 % along track and 70 % across track suit most area routes.

You set it on both area routes, with and without oblique images.

Along track and across track

An area route flies over the site in lines and triggers the camera at fixed intervals. That gives two values:

Overlap along track: how much of the frame two photos share that are taken one after the other on the same line. DJI Pilot 2 calls it frontal overlap.
Overlap across track: how much the photos of two neighbouring lines share. DJI Pilot 2 calls it side overlap.

Rule-of-thumb values

Overlap along track: 80 %
Overlap across track: 70 %
Little texture, trees, tall buildings: 85 % along, 75 % across

Why these values

Airclip Cloud looks for the same point in several photos and works out its position from the different viewing angles. The more often a point is seen, the more firmly it sits in the model.

At 80 % along track, each photo moves on by only a fifth of the frame height. A point on the ground therefore appears in about five photos of the same line. At 70 % across track it also appears on three neighbouring lines. That is enough for a model without holes, and the flight stays short.

When to increase it

The rule-of-thumb values assume a surface with enough texture: tiles, gravel, road markings, edges. Where that is missing, the software finds fewer points it can match and needs more photos to do so.

Uniform surfaces: bitumen and membrane roofing, large photovoltaic arrays, snow, sand, water.
Trees and meadows: leaves move in the wind and look different from one image to the next.
Tall buildings at low altitude: the overlap applies at the height the route is planned for, usually the ground. A roof is closer to the camera, each photo shows less of it, and the overlap on the roof is smaller than the value you set. Increase the values or fly higher.

Two drone photos above a flat roof. On the left from a greater height, the whole building and its surroundings are visible, green tick. On the right from low altitude, the image shows only roofing membrane without edges, red cross. — Left, enough distance: the roof is in the photo with its edges and surroundings. Right, too close: only uniform roofing, and the software finds hardly any points it can match.

What more overlap costs

The two values do not cost the same. More overlap along track only means the camera triggers more often: you get more photos, the lines stay the same. More overlap across track moves the lines closer together, so there are more of them, and every line costs flight time and battery.

If you need to save flight time, save across track, not along track. Going below the rule-of-thumb values rarely pays off: photos missing on the ground cannot be computed afterwards, only flown again.

Point of Interest and Smart 3D Capture

On the two patterns for single buildings you do not set an overlap percentage. With Point of Interest it follows from how many photos the drone takes on the circle. Smart 3D Capture plans it by itself.

Frequently asked questions

What overlap do I need for a 3D model from drone photos?

For an area route, 80 % along track and 70 % across track. Every point on the ground then appears in about five photos of one line and on three neighbouring lines. Over uniform surfaces, trees or tall buildings, increase it to about 85 % along and 75 % across.

What is the difference between overlap along track and across track?

Overlap along track applies between two photos taken one after the other on the same line. Overlap across track applies between the photos of two neighbouring lines. DJI Pilot 2 calls them frontal and side overlap.

Why does my model have holes in the roof?

Often the overlap on the roof is smaller than the value you set. The route calculates it for the ground, but the roof is closer to the camera and each photo covers less of it. Increase the overlap or fly higher. Uniform roofing without texture also needs more photos.

How do I save flight time without making the model worse?

Save on overlap across track, not along track. More overlap along track only costs extra photos, more overlap across track costs extra lines and therefore flight time. Do not go below 80 % along and 70 % across, though.