I have a shapefile includes polygon features of tilted solar panels and I used "Calculate Geometry tool" in ArcGIS to find out the projected area of solar panels (horizontal area).

I am looking for ArcGIS tool or an accurate algorithm to calculate surface area, assuming the tilt angle of solar panels is 40 degree.

I found the following formula:

Surface Area = Planimetric Area / cosine(Slope Angle)
  • in hertzis more simple expresed Nov 20, 2016 at 12:38

1 Answer 1


Your formula

Surface Area = Planimetric Area / Cosine (Slope Angle)

is correct, provided slope angle is measured from the horizontal to the slope (and be sure to convert degrees to radians if the cosine function requires it).

  • Hello Martin, Thank you for your answer, i would like to ask what you mean by convert degrees to radians if function requires it ? the assumed slope angle from horizontal to slope plane.
    – Alfa
    Nov 20, 2016 at 13:50
  • We humans measure angles in degrees (0 - 360 in a circle). However, most computer languages use "natural" angular measures called radians (0 - 2pi in a circle). An end-user tool will, most likely, work in user-friendly degrees.
    – Martin F
    Nov 20, 2016 at 19:57
  • Hello Martin, yeah it needs radians.
    – Alfa
    Dec 9, 2016 at 23:37

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