The purpose of this lab is to solve for the location of an unknown point by observing inaccessible known points. This problem is known as " resection" or " three point problem". The information needed to solve the problem is: two observed angles and given location of three control points. The solution for the problem is in page (401) of the textbook. This will be an approximate solution since the result is a unique solution. The classical ways of solving the problem is by observing more angles and solve for more than one solution. The lab results will be the observed angles and the misclosure error. Point location is the first week's homework.
The technique that will be used is "closing the horizon", page (207) of the textbook. An example of field notes for that problem is in page (208). The idea is to measure the two required angles as well as the angle that closes the horizon as a check. The sum of all the angles should be as close as possible to 3600. For today, an error within one minute will be considered as a good job. Since the purpose of the lab is to learn, the quality of readings will not affect your grade as long as it is within reasonable limits. If readings are very much off, by degrees for example, do not re-observe the points. In that case, try to give a reasonable explanation of the problem.
This is not a group work, but each group will check out one set of equipment. Take the equipment you need and follow the instructor to the roof of More Hall. Set up the theodolite on one of the points on the roof, and aim at any three targets you choose from the list of targets. If you can see Denny Hall, include it in your targets, that will provide a better solution. Remember to record the number of the point you chose to occupy. Assuming you are on point (1) and aiming at points A, B, and C, the measuring process should be in the following order:
Follow the example of page 208 to record the observations, to compute average angles and to compute the misclosure, which is the difference between the sum of the observed three angles and 360o. Remember that solving for the point location is not required for the lab.
What to submit
next lab I expect a short report from each student. First mention your objectives, why did you do that task. Survey Plan is the section where you describe the location of the work you did, do not forget to mention the point number. The next section is Data Acquisition, mention in details what you did. The following sections are: data acquisition problems, results, and finally a copy of your observations. The report should be at least three pages.
What to Check out
A theodolite or a total station, a plumb line, and a tripod.
The last group to leave the roof, is responsible for locking the door. Keep good notes for your self about the theodolite, you may not use it for some labs, and you may be asked about it in any exam. While you are waiting for a theodolite, or after you are done measuring, use the total station to measure the horizontal distance between the total station and the prism. Mention that distance in your results. If you have enough time, explore the total station features.
Students are advised to review figures 11-3, and 11-4