In a DTM/DEM, masspoints and break lines are captured to represent the shape of the terrain. Mass points are irregularly spaced each with X and Y location and Z values typically ( but not always) used to form a TIN. When generated manually, mass points are ideally chosen to depict the most significant variations in the slope or aspects of TIN triangles.The masspoints are representing the bare Z-value (spot height with X,Y and Z information) of the earth surface.
Breaklines are captured in the areas where there is a break or change in slope or continuity.Breaklines are captured on ridgelines, valleys, top and bottom of the slope.These are also used for roads, ditches.All masspoints and breaklines are measured from Aerial Photographs in stereo mode to achieve the  high accuracy on the terrain.

• Generation of elevation models and contours.
• Orthorectification process of aerial photography.
• Visualizing, analyzing and modeling purposes.
• Modelling of hydrographical networks & functions.
• Expansion Model.
• Slope Analysis.

The cameras lens forms a photograph by a bundle of rays. In stereo Photogrammetry a bundle of rays is reconstructed by

1. Inner orientation: Inner orientation is a process by which the image-forming bundles of rays for each photo is reconstructed, true in its geometry. The IO is the process to find the positions and orientation of the film coordinate system of the image obtained by scanner / camera. During this process fiducial points are measured. Before starting IO process, calibration data (i.e. calibrating focal length, radial lens distortion values) is entered in the system.


2. Exterior Orientation: -The relationship with the object spaces is created by exterior orientation of centrally projected image space. Exterior orientation is achieved in two steps:

B. Absolute Orientation: Absolute Orientation relates a model to the ground (object) coordinate system, which establishes a relationship between model coordinates and the true ground coordinates or in other words horizontalization and scaling of the model. During AO, known GCP's locations are measured in the relatively oriented model. This way absolute orientation creates three-dimensional ground coordinates within relatively oriented stereo pairs.

Bundle Block Adjustment: Bundled solution is computed including the exterior orientation parameters of each image of tie points and adjusted GCP’s. A block of images contained in a project is simultaneously processed in one solution. A statistical technique known as least square adjustment is used to estimate the bundled solution for the entire block while also minimizing and distributing error. Block triangulation is the process of calculating the camera or sensor model parameters for each photo with the help of limited number of control points. Once the relationship has been established, accurate imagery and information concerning the earth’s surface can be created.

Orthorectification or Orthophoto Generation is a process of removing the effects of tilt, relief, and many of the lens aberrations from standard perspective photographs.
Orthophotos are maps, created by geometrically corrected Aerial Photographs.We create digital orthophotos using Datum software.

Digital orthophoto are used as maps, for visual identification, also with combination of other mapping products like DTM and contours.

To generate a digital orthophoto that most closely achieves the resolution of the continuous tone, original aerial image, we apply a variety of image enhancement and edge sharpening routines using special Image Processing techniques.
The process involves color / contrast matching and feathering techniques to ensure a virtually seamless mosaic. Many images can be mosaicked together and resampled to produce an overview image file to supplement the original orthoimages. Accuracy is measured by comparing the rectified position of ground control point to the true coordinates of the point.