Aerial photographs are those images that are taken from the air from an aircraft or using a drone. Altitude Imaging suggests using highly-accurate cameras for clearer images. According to the experts at entrepreneur.com, there are different things to consider while taking an aerial photograph, like, film, overlap and scale. There are several more terms used in relation to aerial photography have been explained below for your convenience:
Most of the time aerial photographs are taken using black and white film. Interestingly infrared, color and even false-color films are used for specific projects at times.
The focal length can be defined as the distance from the focal place to the center of the camera lens. When the focal length increases, the image distortion goes down. Experts measure the focal length accurately when the camera is being calibrated.
The scale is actually the ratio of the gap between 2 points on an image to the real distance between the exact 2 points on the ground. Sometimes experts use the scale of the photo as well to determine the ratio between the focal length of the camera and the altitude of the plane. Scale is usually represented in any of the three following ways
· Unit equivalent
· Representative fraction
Large scale photos tend to cover smaller areas in better detail. The ground features are clearer and detailed in such images. In a small scale photo, larger areas are covered in lesser detail. The area of ground seen in a small scale photo will be more when compared to a large scale image.
These are tiny registration marks that are seen at the edges of an image. The distance between these marks is accurately measured when the camera is being calibrated. This information is usually used when creating a topographic map by cartographers.
The overlap refers to how much area in one photograph appears in another photograph. It is usually expressed in the form of a percentage. Photo surveys usually have sixty percent forward overlap as well as a thirty percent lateral overlap.
This is the 3D view that is seen when two photos that overlap are seen through a stereoscope. Each image of the pair shows a different view of the same place, which tricks the brain into interpreting it as a 3D image.
Roll And Photo Numbers
Each image taken in aerial photography is given a specific index number related to the image’s roll as well as the frame. This helps to identify each image as well as other important data like the plane’s altitude, weather conditions, and camera focal length and so on.
Flight Lines And Index Maps
After every photo mission, the aerial surveyor plots the locations of the 1st, last as well every 5th image centre, including the roll and frame number on an NTS map. Small circles represent photo centre and the straight lines connecting the circles show the flight line. This is called an air photo index map and lets you relate images to their actual geographical location.