COGO Tools in SuperGIS Desktop 3.2
What is COGO?
COGO is the short for coordinate geometry, which is a reference system used to measure horizontal and vertical distance on a planimetric map, as shown in figure 1. It is usually created by civil engineers to record their field survey data, including the distance and direction for straight lines, and angle, radius, arc length, and other COGO measurements for curved lines. To record the surveyed data, the civil engineers use a known location as a reference/base point, and then record down the distances and directions of other surveyed points relative to the reference/base point.
There are different ways for the civil engineers to record the straight lines and curved lines. One of the most commonly used ways is called traverse, which simply describes the direction, distance, angle, arc, or other measurements of the COGO lines. Most of the COGO lines can be record in the form of traverse line. Another way is called 2-Point line. The civil engineers set a start point and record the location of the end point relative to the start point using various methods. This is useful when the civil engineers want to record lines between some existing lines. The other way is call offset line, which describes the location of the line vertexes relative to a chosen centerline. It helps the civil engineers to describe boundaries on either side of a specified centerline.
Figure 1: An example of land survey plan.
COGO in GIS
In GIS, COGO refers to a data conversion process in which a digital map is constructed from written descriptions, such as the survey plan data of land parcel boundaries. By its original definition, COGO is a command structure problem oriented language to solve geometric problems. It originates from a MIT’s subsystem of Integrated Civil Engineering System (ICES) in the 1960s, and is related to the LOGO language used to create precise descriptive data tied to the ground surface.
Nowadays, the COGO tools are used to create or edit vector data in GIS systems with precision surveying data such as land surveying data. In order to match the descriptions, such as directions and distance, used by the civil engineers, the COGO lines in GIS systems have a specific rule: They are either completely straight or completely circular. By following the rule, the surveyed data can be precisely re-created in the GIS systems.
SuperGIS Desktop 3.2 with COGO
The COGO tools are now available with the latest version of SuperGIS Desktop 3. It provides users different ways to create new COGO lines, including Traverse, 2-Point Line, Offset Line, Cul-De-Sac, and Split Line Proportionally. Users can now use SuperGIS Desktop to precisely build their COGO lines. The COGO tools in SuperGIS Desktop 3.2 include edit tools, information tools, and other tools.
Figure 2: COGO tools in SuperGIS Desktop 3
The Edit Tools
The edit tools help users to re-create the COGO lines record in the survey plan, including traverse, 2-point line, offset line, cul-de-sac, and split line proportionally. These tools are designed to match the way civil engineers record the data, so that they can create the COGO lines as the way they do the record. The traverse tool is for creating features that are collected in the form of directions and distance, or angles and distances. The 2-point line tool helps users to create lines between existing features. Both traverse and 2-point line tool provides 4 courses to set the segments, including direction-distance and angle-distance for straight lines, and curve and tangent curve for curve lines. The offset line is used when the survey data are in the form of strip descriptions, which describes boundaries on either side of a specified centerline. The cul-de-sac tool helps users to build a dead-end turnaround by assigning the turnaround radius, street width, and return radius. The split line proportionally tool helps to split line features into segments proportionally, based on the segment proportions provided.
The Information Tools
The survey data, including the directions and distances of line features, are measured on the surface of the Earth, which are called ground measurements. But the directions and distances of the line features in SuperGIS Desktop are projected data, which are called grid measurements. The two measurements are often different and need to be converted. Ground To Grid Conversion tool is one of the COGO information tools that helps to convert the 2 measurements. Other tools in the information tools, including report, area calculator, and curve calculator, can help users to get COGO descriptions in both ground and grid measurements.
The other tools includes convert to COGO lines tool and update attribute tool. The first one helps users to convert existing line into COGO lines that match the rule of being completely straight or circular. The second one helps users to get the COGO descriptions of the selected lines in their attribute table.
The COGO approach has been used by civil engineers since the early 1960’s developed by MIT’s ICES. It is useful for those who want to precisely convert the human-made features in written descriptions to digital forms. Now the latest version of SuperGIS Desktop 3.2 provides its users the COGO tool. With the tool, you are able to re-create the COGO lines in SuperGIS Desktop as the way civil engineers record their survey plans. In addition to the rich COGO editing tools, there are also information tools and other helpful tools that assist you in getting COGO information and help you create and manage the COGO features.