WGS84 Conversion:

WGS84 is the spherical coordinate system of latitude and longitude adopted by GPS and used extensively for navigation. Maps however are drawn using a Cartesian system and so a mathematical conversion is required to ‘flatten’ the spherical system. In addition, whilst the spherical system assumes the earth is a spheroid Surveyors need to work with the more precise Geoid which describes the equipotential plane of the earths surface. Much work has been done by the Ordnance survey of Great Britain in building a Geoid model and we are much indebted to their open source data that is used in this conversion utility. Currently the converter only converts to the UK system of OSGB36 but other areas are being added to user requests.

Least Squares Transformation:

Least square’s uses regression analysis to determine the most probable measurement from groups of measurements taken under different conditions. The term least squares is born from each point once a solution is found having a residual and the best solution is when the sum of these residuals squared is a minimum. Cogeo employs this method to determine the necessary transformation parameters to convert from one coordinate system to another given groups of coordinates in each system of matching points.

Star Azimuth:

The stars are the most effective way of determining direction and a surveyor by reference to an almanac can take angular observations to a star and determine the azimuth to another point by reference to it once he has entered the stars declination for the time of the observation and approximate latitude

Resection:

The position of an observer may be determined by measurements to known points and this method is known as resection. Several mathematical solutions are possible from angular and distance measurements. CoGeo will let you select the measurements to use and display the resulting position using those measurements.

Level Book:

Heights are often determined by measuring height differences from a known point using a ‘spirit’ level. This is an optical device which relies on gravity to form a line of sight parallel to the earths surface and latest spirit levels work automatically reading heights from a bar coded staff. A common method of booking these observations is the height of collimation method and is reduced to heights using simple arithmetic. The surveyor closes his levelling run onto a known point and will find an error which if it is within reasonable bounds he will distribute amongst his observations to determine the most probable height of each point. CoGeo provides a convenient electronic booking sheet which reduces the observations and distributes the error appropriately. If a digital level is used then the book may be connected to the instrument to trigger it’s measurement and record the data.

Land Surveyors measure the terrain in 3D and produce accurate detailed maps and plans. The work involves using several types of instruments to do this including optical spirit levels, theodolites, laser and infra red distance measuring equipment and GPS. A variety of methods are used to compute these measurements and in many cases solve the most probable solution from groups of measurements.
CoGeo is a tool designed to perform these calculations in a seamless and effective manner.

Traverse:

Traversing involves measuring a series of angles and distances between points on the ground starting at a known point and ending on a known point, most often the start point again. The measurements are never perfect and errors will accumulate throughout the traverse with a residual error at the closing known point. These errors are then distributed and several recognised methods can be employed to distribute these residuals so that the best probable solution is determined for all of the points.