Photogrammetry

Layer informatics provides complete solutions on all tasks of Digital Photogrammetry such as Aerial Triangulation, Stereo Compilation, DSM/DTM Extraction, Orthophoto Production, Radiometry Adjustment and Mosaicking.

Aerial Triangulation

Aerial Triangulation is the primary component of any photogrammetry project and involves the calculation of true ground coordinates of individual points from photo coordinate measurements. The main objective of aerial triangulation is to connect and increase ground control points through strip and or block for other photogrammetric operations.

Normally performed in two stages as interior orientation (relating the pixel coordinates of the digital image to the photo coordinate system and often involves the measurement of fiducials for the frame images) and Exterior orientation (analytically determine the position of the camera station and the attitude of the camera at the instant of exposure, involves the measurement of pass/tie points and orienting the model coordinates to the ground).

As the increased number of point measurements improves the solution, the tie points are selected using the auto-correlation techniques and manually edited if required. The Air Borne GPS values (Use of GPS in the aircraft to determine the positions of camera exposure stations) are also used in the adjustment to strengthen the solution. The following are the inputs required to perform aerial triangulation...

  • The flight path
  • Camera calibration certificate
  • Coordinates , descriptions and the accuracy of the ground controls
  • Projected accuracy of the final AT solution
Stereo Compilation

Stereo compilation refers to the mapping of vector features from oriented stereo pair (pair of overlapping photographs) in 3 dimensions. Our advanced softcopy plotter enables us to capture vector data from models of diverse scales and deliver the high quality digital topographic maps in industry standard formats.

DTM/DEM Extraction

A DTM (Digital Terrain Model) is a three dimensional representation of a terrain’s surface whereas a DEM (Digital Elevation Model) is a subset of DTM characterized by a regular spaced grid of points representing the terrain. The DTM/DEM has a wide range of applications from contour generation to superior Ortho-Photo production.

Orthophoto Production

An Ortho-Photo is a rectified aerial photograph geometrically corrected for relief and tilt displacements. The scale of an Ortho-Photo is uniform and hence can be used to measure true distances. It is a photomap which has the geometric qualities of a map and a pictorial representation of a photo. An Ortho-Photo has a variety of functions, the most common being a backdrop for feature extraction in GIS applications.

Layer informatics boasts of sound expertise in producing Ortho-Photos of varied pixel sizes (as high as 4cm GSD), in different bands (RGB & CIR) and over terrains ranging from a flat, semi built to highly undulated and complex built-ups.

Seamlines were automatically generated and manually edited in the center of the overlapping Orthos and were mosaicked to the tiles of required dimensions with a suitable feather. The tiles were then edited in an image editing software where the team is adept at fixing the color differences along the seam joints and performing localized and global radiometric adjustments.

The team also specializes in creating a pan sharpening product (a process of producing high resolution color imagery from a high resolution Panchromatic and a lower resolution multispectral imagery).

The final Ortho’s will be delivered as tiles in industry accepted standard formats.