The disclosure presents novel methods to conduct aerial surveying, inspection and measurements with higher accuracy in a fast and easy way, comprising: (1) flying a drone with an accelerometer, gyro, and camera sensors over a target object; (2) capturing a first aerial image at a first position; (3) capturing a second aerial image at a second position, wherein the second position has a horizontal and vertical displacement from the first position; (4) calculating the displacements between the first and second location using a sensor fusion estimation algorithm from the position sensors' data; (5) solving for the pixel depth information of the aerial images by using a single-camera stereophotogrammetry algorithm with the relative altitude and horizontal distance; (6) deriving the ground sample distance (GSD) of each pixel from the calculated depth information; (7) using the image pixel GSD values to compute any geometric properties of the target objects.