COGO is an abbreviation for coordinate geometry. It is a standard term in the field of surveying and refers to data collection methods that use distances, bearings, and angles to establish survey points. If you are not a surveyor, you may need to understand a little about COGO in order to correctly interpret and manage point data that comes to you from surveyors or from field crews who have used COGO methods to collect data. For example, a field crew has just placed two new streetlights and you need to add those new assets to the database using AutoCAD Map 3D. You receive two sketches from the field crew with some crosses and numbers on them (see the illustration below).
Even though these sketches are crude, they contain all the information you need to correctly place the new assets, provided that you already know, or can find, the general area (street and intersection) where the work has been carried out.
In the first example, in the sketch above, on the left, the field crew has established the location for the new street light using the COGO method of distance/distance. This is a quick and easy method that only requires a tape measure. They started from two known points, in this case the corners of two lots, and measured the distance from those points.
In AutoCAD Map 3D, you can reproduce the distance/distance measurements and place the street light accurately using a COGO command. The illustration on the left below shows the base map open in AutoCAD Map 3D and the work site located (compare with the sketch above). The illustration on the right shows the COGO distance/distance command in progress. When you select the start points and the distances, a calculation is performed using two intersecting arcs. The start points are indicated by the black tripod symbols. There are actually two possible locations because there are two points where the lines intersect. However, it will be obvious which one is correct. The final location is indicated by the red symbol.
In the second example, in the sketch on the right, the field crew established the location of the new street light using the bearing/bearing method. In this case, the crew had to work on a busy street and could not drag a tape across it. Instead they started from two known points and then took compass bearings from those points.
In AutoCAD Map 3D, if you have this kind of source data, you can use the bearing/bearing command to place the asset. The illustration on the left below shows the base map open in AutoCAD Map 3D to the location of the work site (compare with the sketch). The illustration on the right shows the COGO bearing/bearing command. The black tripod symbols are the start points, the black lines are the bearings, and the red symbol is the location of the street light.
The first animation demonstrates how to use the COGO distance/distance command to establish the location of a point. This animation accesses the COGO command from the Survey task pane and adds the point to an existing survey points database.