# Calculate surface area from horizontal area and angle

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 `hertz`is more simple expresed – ronzano cukaj Nov 20 '16 at 12:38

``````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. – yanni joni Nov 20 '16 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 '16 at 19:57
• Hello Martin, yeah it needs radians. – yanni joni Dec 9 '16 at 23:37

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