Overlapping Aerial Photographs Capturing by Drones - Principles

Introduction

These days the 3D modeling from photographs getting more popular. No of Software facilitate these functions in the GIS and Mapping arena. However some of the giant market leaders covered up 90% the market. Those are,

1. ContextCapture (Previously Known as Acute3D) From Bentley Systems

2. Drone2Map from ESRI.

3. Pix4D

These Software are requesting minimum 60% overlapping images for preparing 3D models. But most of the Drone Manufactures did not provide the functionality of Capture Overlapping Photos on their Native Remote Controlling units. For example DJI. Then We Need to do this in Manually (See Here). So How we can do? For that we need to understand Some Principles of Digital Photography.

1. Sensor Size.

Every Digital Camera have a Image Sensor. When you doing a Aerial Photography you should know the your Camera Sensor Size. Its Generally measure in millimeters. Most of the sensors are Not in Square so you should understand your camera sensor width and length. these details can be found in your camera Manufacture Handbook.

2. Image Size

Image dimensions are the length and width of a digital image. It is usually measured in pixels. Generally The image size is not a fixed value for a camera. You can change as you wish. In aerial photography for 3D modelling the large image size is recommended. Hence Set your Camera maximum image size.

3. Pixel

In digital imaging, a pixel, pel, dots or picture element is a physical point in a raster image, or the smallest addressable element in an all points addressable display device; so it is the smallest controllable element of a picture represented on the screen.

4. Pixel size

Pixel size means how much length of a pixel.

Pixel size = Sensor length / Image length.

For exmple of DJI Phantom 3 Professional Camera:

Pixel Size = 6.16 / 4000

                 = 0.00154 mm

5. Focal Length

The focal length of the lens is the distance between the lens and the image sensor when the subject is in focus, usually stated in millimeters (e.g., 28 mm, 50 mm, or 100 mm). Normally the Drone Camera have fixed focal length.

6. Flight Height

Flight Height Means your drone flying Height. Normally Drones have Capable of flying in 120 m above the Ground in good weather condition. 

6. Ground Sample Distance

The Ground Sampling Distance (GSD) is the distance between two consecutive pixel centers measured on the ground. The bigger the value of the image GSD, the lower the spatial resolution of the image and the less visible details.

Normally the Accuracy of the Model is twice of Ground Sample Distance. Hence If your Ground Sample Distance is very low then your Model become High Accuracy.

GSD = Pixel Size X Flight Height / Focal Length.