**1. Geodetic Control Survey**

**1.1 Establishing large area Geodetic control Network**

A **geodetic control network** (also **geodetic network**, **reference network**, **control point network**, or **control network**) is a network, often of triangles, which are measured exactly by techniques of terrestrial surveying or by satellite geodesy.

A geodetic control network consists of stable, identifiable points with published datum values derived from observations that tie the points together.

Classically, a control is divided into horizontal (X-Y) and vertical (Z) controls (components of the control), however with the advent of satellite navigation systems, GPS in particular, this division is becoming obsolete.

The higher-order (high precision, usually millimeter-to-decimeter on a scale of continents) control points are normally defined in both space and time using global or space techniques, and are used for “lower-order” points to be tied into. The lower-order control points are normally used for engineering, construction and navigation. The scientific discipline that deals with the establishing of coordinates of points in a high-order control network is called geodesy, and the technical discipline that does the same for points in a low-order control network is called surveying.

**1.2 Establishing geodetic control for Construction**

Conventional surveys are those performed using traditional precise surveying techniques and instruments–i.e., theodolites, total stations, and levels. Conventional control surveys can be used to economically and accurately establish or densify project control in a timely fashion. Quality control statistics and redundant measurements in networks established by these methods help to ensure reliable results. However, conventional survey methods do have the requirement for intervisibility between adjacent stations.

GPS satellite surveying techniques can often be used to establish or densify project control more efficiently (and accurately) than conventional control urveying techniques– especially over large projects. As with conventional methods, quality control statistics and redundant measurements in GPS etworks help to ensure eliable results. Field operations to perform a GPS survey are relatively easy and can generally be performed by one person per receiver, with two or more receivers required to transfer control. GPS does not require intervisibility between adjacent stations.

The most important addition to the geodetic surveying community was the introduction of the Navstar Global Positioning System (GPS), allowing the surveying industry to establish affordable, high-accuracy geodetic control. These new technological developments, along with the skills o f trained professionals, will aid in the establishment o f a geodetic control network for cities, states, and counties that plan to implement a Geographic Information System (GIS) or some other Construction Project.

**1.3 Establishing geodetic control for Topographical survey**

Control surveys establish a common, consistent network of physical points that are the

basis for controlling the horizontal and vertical positions of transportation mprovement projects and facilities. Corridor control surveys ensure that adjacent projects have compatible control. Project control surveys provide consistent and accurate horizontal and vertical control for all subsequent project surveys — photogrammetric, mapping, planning, design, construction, and right of way.

Surveying is based on geodesy. With precise survey instrument, the Earth must be treated as an ellipsoid instead of a sphere. The ellipsoid that is chosen for geodetic survey is called reference ellipsoid. The shape of the Earth, so called geoid, is expressed as an equipotential surface of gravity. Usually, position on the ground is measured in longitude, latitude on the reference ellipsoid and height on the geoid. For convenience to measure the three dimensional values, a lot of monuments whos e longitude, latitude or height is known are settled as referen ce point all over the countries. Control point surveying is a surveying to establish the reference point network, determine the coordinates of a new point based on the reference point network. Some precise measuring instruments such as total station and level are used for the surveying. In addition, rapid development of the space geodesy enables us to establish an international reference frame covering the whole globe.

**1.4 Traverse surveying/Control densification**

The densification of control points mostly require for setting out construction survey and as well topographical feature survey in construction project mainly Rail way, Road and Industrial construction project.

high-precision GPS/GNSS measurement are being used in the topographical mapping for road, Rail, pipe line, and other surveying related to infrastructure development. The engineer wants actual ground measurement which equal to plane geometrical calculation. However, when utilizing high-precision GPS measurement for topographical location purposes, there is a significant but usually unanticipated problem that must first be addressed if accurate measurements are to be made. Simply put, unless proper correction methods are used, horizontal distances between two locations determined by the GNSS method will differ from the Totalstation method.

There are two way of traversing or control densification a. The conventional method using Theodolite/Totalstation and b. First static measurement using GNSS with scale factor reduction/ground coordinate calculation. Now a day it can be done through mathematical calculation. Measurements that are made by traditional survey methods ie the totalstation. This difference between the two measurements is often referred to as the grid-to-ground problem. It is always identical and requires resolving with mathematical calculation. “Geosystem Corporation” is ready to solve for you.