DIFFERENT METHODS OF SURVEYING Part (C) Aerial Surveys

Aerial survey is a method of collecting information conducted from an airborne platform. This is collected by using aerial photography, Liar or laser scanning. It is often recognized similarly as aero photogrammetry, part of photogrammetry where the camera is mounted on an aircraft. Aerial survey is different to satellite imagery because of its better resolution, quality and atmospheric conditions. Technical Data used in the field explained in civil surveyor course in Rawalpindi.

Photogrammetry is the practice of determining the geometric properties of objects from photographic images. This involves estimating the three dimensional coordinates of points on an object. These are determined by measurements made in two or more photographic images taken from different positions. Common points are identified on each image. A line of sight (or ray) can be constructed from the camera location to the point on the object. It is the intersection of these rays (triangulation) that determines the three‐dimensional location of the point. Some more details of civil surveyor course in Rawalpindi are as under.

In the simplest example, the distance between two points that lie on a plane parallel to the photographic image plane can be determined by measuring their distance on the image, if the scale of the image is known. The images are obtained by mounting a camera on an aircraft which points vertically down towards the ground. Multiple overlapping photos of the ground are taken as the aircraft flies along a flight path. These photos are processed in a stereo‐plotter (an instrument that lets an operator see two photos at once in stereo view).Generally the higher you fly the less points you have per square meter and your pixel resolution worsens. Photogrammetry is more accurate in the x and y direction while range data is generally more accurate in the z direction. The range data can be supplied by techniques like LiDAR and laser scanners.

Airborne LiDAR is a highly cost effective means of collecting detailed topographic survey information, and offers significant advantages over traditional forms of topographical survey in terms of speed, access, resolution, accuracy and canopy penetration, for a variety of applications.

LiDAR – Light Detection and Ranging is a method of detecting distant objects and determining their position or other characteristics by analysis of pulsed laser light reflecting from their surfaces. Basically a laser pulse is reflected from a rotating mirror inside a laser scanner. By measuring the time delay between when the laser pulse is emitted, and when it returns to the scanner, the distance between the scanner and the object can be precisely determined. The scanner can also accurately measure angles. When all of the distance, angular and positional information is processed the scanner can produce highly accurate 3 dimensional data set, which is sometimes referred to a point cloud. Photos can clearly define the edges of buildings when the point cloud footprint cannot. Therefore often the orthorectified images are draped on top of the Lidar grid thus creating a 3 dimensional visual survey. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join civil surveyor course in Rawalpindi.