UNIT 25: USING COGO FOR DATA INPUT
Written by Ross Miller, British Columbia Institute of Technology
Coordinate Geometry (COGO) is a method of inputting surveying or engineering data into GIS, CAD or mapping softwares. These data may be collected in the field using conventional surveying techniques and instrumentation, or may be derived from existing maps, plats, engineering plans, drawings or records.
Data collected in the field consist typically of coordinates of points, distances and bearings between points, and point identifiers (with possibly additional descriptions for these points). The data are observed and recorded through standard field surveying procedures, such as a traverse or a series of layout measurements. The data may be non-digital (recorded in notebooks), or digital (recorded on some sort of total station or data logging device) In the latter case the data will be transferred to office computers through specialized software.
Existing maps and plans include subdivision plans, showing legal lot boundaries, and engineering drawings. In both cases features are depicted with some coordinate values, and distances and bearings or offset distances are shown between the features.
The City of Abbotsford has developed a reasonably accurate cadastral base for their GIS implementation, but a more accurate data set is required to support future engineering applications. To achieve this, the cadastral base map is being improved in an incremental fashion, using COGO to enter new field survey data as it becomes available. City survey crews collect some survey data when they tie in property corners at major intersections during routine surveys, and legal survey plans from the Land Title Office are frequently acquired when new subdivisions are developed.
The GIS technician is responsible for entering the field and plan data into the GIS software using the COGO module. She also must check the data carefully, and adjust the data sets, in consultation with the City Surveyor and the GIS manager, to ensure a good fit with the base map as a whole.
The following list describes the expected skills which students should master for each level of training, i.e. Awareness/Competency/Mastery.
The expected learning goals of this section are to achieve a general understanding of COGO, its potential uses, and a working knowledge of basic COGO vocabulary.
The learning goals of this section are to develop the ability to perform common COGO operations.
The learning goals of this section are to be able to perform more advanced technical operations associated with field survey data and COGO.
Recommended:
Unit 4 - Land Records
Complementary:
Unit 11 - Registration And Conflation
Other Recommended
General: Knowledge of applications and survey measurement practices which utilize field surveying/cogo regularly - for example municipalities, forestry, utility, civil engineering , energy/gas/oil/pipeline companies
For Competency and Mastery levels, thorough knowledge of coordinate systems, field surveying methods and plane survey computations
For Mastery level, knowledge of survey data adjustment procedures
At the completion of these exercises, the student will be able to
Vocabulary
Topics
What is COGO ?
What is the relationship of COGO to CAD, GIS, engineering software?
What is the relationship to other methods of data input ?
Who uses COGO ?
How is COGO accomplished ?
Advantages and Disadvantages;
Advantages - accuracy, adjustment of measurements, automated feature generation, attribute tables, links to surveying and engineering activities, automated transfer of data
Disadvantages - time, cost of conversion
Learning Objectives:
Vocabulary
(see 'Other Recommended' above, for prerequisite knowledge for this section)
Topics
Setup a COGO session in GIS/CAD software
enter data into COGO
editing of COGO data
Learning Objectives:
Vocabulary
(see 'Other Recommended' above, for prerequisite knowledge for this section)
Topics (requires good background in civil, forestry, survey field methods and measurements)
Import field data
Editing Data
Adjustment of Measurements
A list of GIS Resources.
ARC/INFO COGO manual, ESRI, esp. Cranes Roost exercise. ARC/INFO COGO is an optional module for workstation and NT ARC/INFO. The ARC/INFO documentation provides an excellent overview of the COGO module. The Crane's Roost Exercise is a lengthy one, but can be used at the introductory and intermediate levels.
Lab Exercise This exercise is written for Arc/Info COGO, but the data set can be easily used with other software. The exercise takes about 2-3 hours to complete. It involves coordinating a subdivision plan, and makes use primarily of traversing, sideshots, and curve layout operations. However the data is such that more advanced exercises can be introduced. For example, depending on how the student computations are done, it may be necessary to balance the traverse, break some lines, apply multiple distances along a bearing. In addition the exercise can involve placement of annotation directly from the attribute tables, and the use of other ARCEDIT functions for copying some lines (including snapping). The exercise can be used at all levels. There are also Powerpoint lecture notes for this exercise, covering basic terms and features of COGO, in particular ARC/INFO COGO
Microstation and CivilDraft
Instructors who have the Microstation Geoengineering Academic Suite will also have Geopaks CivilDraft software. This provides extensive COGO capabilities within Microstation. Alternatively, Autocad software can be used in conjunction with Softdesk civil engineering software to introduce COGO.