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      Step 1. Before Starting a Project > 1. Designing the Image Acquisition Plan > c. Computing the Image Rate for a given Frontal Overlap - PIX4Dmapper

      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.


      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)

      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]

      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)

      Note: x is given in [m], considering that the GSD is in [cm/pixel].

      Combining the equations (3) and (5):

      t = x / v = ((imH * GSD) / 100) * (1 - overlap) / v (6)

      Example: In order to achieve an overlap of 75% (overlap = 0.75) and a GSD of 5 [cm/pixel], supposing that the image height is 4000 [pixels] and the speed of the UAV/plane is 30 [km/h] = 8.33 [m/s], based on the equation (6), the image rate should be 6 seconds:

      t = ((imH * GSD) / 100) * (1 - overlap) / v = ((4000 * 5 ) / 100) * (1 - 0.75) / 8.33 = 6 [s]

      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:

      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)

      Note: The result is given in [m], considering that the GSD is in [cm/pixel].

      Combining equations (3) and (8):

      t = x / v = ((imW * GSD) / 100) * (1 - overlap) / v (9)