• 5-10 pixels for minimum recognition
• 20-40 pixels for reliable shape classification in real conditions (sun glare, motion blur, angle, etc.)
• Ground sample distance (GSD) = dimension/pixels
• 1 ft square and 20 pixels à GSD = 1 ft / 20 = 0.6 in/pixel

• Camera resolution and field of view are set parameters, e.g. 2 MP (1080p x 1920p) and 51 deg FOV
• Ground width = 2htan(FOV/2), where h is altitude
• Ground width = 250fttan(25.5 deg) = 48 ft
• GSD = 48 ft / 1080p = 0.5 in/pixel