An Orthophoto can be defined as an aerial photograph which is free from relief distortions, anomalies arising from camera lens & aircraft’s flying attitude (Roll, Pitch & Yaw OR Omega Phi Kappa). An Orthophoto combines the image characteristics of an aerial photograph with the geometric qualities of a map showing all ground features in their correct ground positions facilitating direct measurement of distances, areas, angles, and the detailed portions of ground features that may be generalized on traditional maps. An Orthophoto fulfills a fundamental role as a geometrically accurate base map.
2D & 3D Topographical mapping
Consists of digital data collection and creation of topographic map using the stereo plotting equipment. According to the specifications provided, the mapping must show all topographic details visible on the photography (with the exception of street hardware) that can be shown clearly at a scale of 1:2500 photographs. Particular care is often taken to show all fences, cut lines, and other evidence of land occupation. Features such as quarries, gravel pits, open pit mines, log piles, coal, sand and slag piles etc. are shown by areas (polygons).
Digital Terrain Model (DTM)
A digital terrain model (DTM) also consists of mass points (X, Y) with elevation values (Z) but unlike the DEM, the mass points are not in the form of a regularly spaced grid. The mass points are placed randomly as per the undulation of the terrain and the density of points can be adjusted so as to represent the actual terrain. In other words, lesser mass points can be used in a flat area more mass points can be captured to describe undulating terrain. Breaklines (to depict sudden change in the terrain) are also an integral feature in a DTM, besides the mass points.
3D City Modeling
A 3D city model can be defined as a three-dimensional depiction of a city. A 3D city model consists of a digital elevation model (DEM) and 3D building data (building polygons). The building polygons are extruded on the basis of their elevation versus that of the ground (DEM). A 3D city model is used in a variety of fields including but not limited to urban planning, telecommunications, infrastructure development & tourism etc.
LiDAR (Light Detection And Ranging) is a method of generating precise and directly georeferenced spatial information about the shape and surface characteristics of the Earth. It has become an established method for collecting very dense and accurate elevation data across landscapes, shallow-water areas, and project sites. LiDAR is typically "flown" or collected from planes where it can rapidly collect points over large areas. LiDAR can also be collected from ground-based stationary and mobile platforms. These collection techniques are popular within the surveying and engineering communities because they are capable of producing extremely high accuracies and point densities, thus permitting the development of precise, realistic, three-dimensional representations of railroads, roadways, bridges, buildings, breakwaters, and other shoreline structures.