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The image shooting rate to achieve a given frontal overlap depends on the speed of the UAV/plane, the GSD and the pixel resolution of the camera.
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D = distance covered on the ground by one image in the flight direction [m] overlap = percentage of desired frontal overlap between two images od = overlap between two images in the flight direction [m] x = distance between two camera positions in the flight direction [m] v = flight speed [m/s] t = elapsed time between two images (image rate) [s] |
Figure 1. |
From Figure 1, we obtain the following equations:
od = overlap * D (1)
x = D - od (2)
t = x / v (3)
Two cases are possible:
- Camera oriented with the sensor width (long dimension) perpendicular to the flight direction (usual case)
- Camera oriented with the sensor width (long dimension) parallel to the flight direction
Camera oriented with the sensor width (long dimension) perpendicular to the flight direction (usual case)
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D = Dh = (imH * GSD) / 100 (4) Where: Dh = distance covered on the ground by one image in the height direction (footprint height) [m] imH = image height [pixel] GSD = desired GSD [cm/pixel]
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Figure 2. Sensor width placed perpendicular to the flight direction. |
Combining Equations (1) and (4) into Equation (2):
x = Dh - overlap * Dh
x = Dh * (1 - overlap)
x = ((imH* GSD) / 100) * (1 - overlap) (5)
Combining the equations (3) and (5):
t = x / v = ((imH * GSD) / 100) * (1 - overlap) / v (6)
Camera oriented with the sensor width (long dimension) parallel to the flight direction
If the camera is placed on the plane / UAV having the sensor width (long dimension) parallel to the flight direction:
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D = DW = (imW * GSD) / 100 (7) Where: DW = distance covered on the ground by one image in the width direction (footprint width) [m] imW = image width [pixel] GSD = desired GSD [cm/pixel] |
Figure 3. Sensor width placed parallel to the flight direction. |
Combining equations (1) and (7) into the equation (2):
x = DW - overlap * DW
x = DW * (1 - overlap)
x = ((imW * GSD) / 100) * (1 - overlap) (8)
Combining equations (3) and (8):
t = x / v = ((imW * GSD) / 100) * (1 - overlap) / v (9)
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