GEOG 2043

LAB 5

Surveying 2: Total Station

BACKGROUND:A total station is an electronic laser that measures and computes distances using simple mathematics and timing. The total station sends an infrared laser that is reflected from a prism and sent back to the total station. The time that it takes the laser to reach the sire and return determines the slope distance to that point. Based on the vertical angle of the instrument based on a flat horizontal angle of 90 degrees, the total station can calculate the horizontal distance and vertical difference.

What does the total station look like?
 

A total station, or electronic theodolite, is helpful for collecting data in a variety of situations. For example, it is difficult to measure the width of very large rivers like the Rio Grande or the Colorado. A conventional method of tape measurement would be difficult, if not impossible. The total station provides a quicker solution to this measurement by allowing a light beam to measure the distance instead of a tape measure. The total station can also be useful in situations where large relief is present. For example, you may want to measure the characteristics of an avalanche track, beginning at the starting point and working through the runout zone. It would be tedious to do this with a level, and standard topographic maps would not provide sufficient detail. The total station allows measurement of this type to be taken by simply targeting someone as they move down the avalanche chute (assuming it's safe to do so). The total station is also very useful for doing small topographic surveys of study sites. Graduate students in Geography have used the total station to lay-out a grid network for measuring snow depth on Niwot Ridge.  Another student has used the total station to map the topography of the ground surface to see how this affects variations in snow depth and pathways for meltwater.

INSTRUCTIONS FOR SET-UP

Cautions

• Total stations are relatively expensive (cost = $8,000 -12,000), thus you should be VERY careful when handling the instrument.
• Never point the instrument directly at the sun. Direct sunlight can damage components in the instrument and your eyes.
• Avoid wet conditions, including rain and snow, at all times. If the instrument gets wet, the electronics can be irreparably harmed. The instrument is not water proof.
• Keep all the fine adjustment knobs loose and unlocked during transport, or if the instrument is not recording information. Keeping the knobs locked can strip the locking mechanisms.
• The black knob with a white dot controls a locking mechanism that locks the instrument to a plate. This knob must be tightened to keep the reference zero angle consistent during data collection.

Setup of the Total Station

• Set the tripod over the control point with the legs equally spaced at chest level.
• Carefully place the instrument atop the tripod and use the screw on the tripod to secure the instrument at its base.  Never let go of the instrument until you have it firmly attached to the tripod.
• Look through the optical plummet at the side of the instrument. You must re-focus the view and get the crosshairs in site over the control point. Put the survey control point at the center of the cross hairs and set the tripod legs into the ground. Pivot the tripod on one leg and move the other two until you are over the control point. The tribract at the base of the instrument can be moved a small distance horizontally to achieve your final position.
• The fine leveling is done with the three screws on the tribract. Use your thumbs to move two screws at a time. Once you are close, turn the instrument 90 degrees and use the other screw to move in the perpendicular direction. This process works best through trial and error.
• At this point the instrument should be level and over your control point. Look through the optical plummet to confirm.
• Push the green button to turn on the instrument. Be sure that all the motions are loose except for the black knob with the white dot, which needs to be tight. Rotate the instrument vertically and horizontally to clear the machineís memory.

• Take a backsight measurement on a control point within the line of sight. You must have a zeroing point from which to collect your data so you know how to orient the data once it is collected. There are horizontal and vertical motion screws that will lock and allow fine motion with the outer of the two screws. Before zeroing, the rule of thumb is to locate the base of the prism rod with the crosshairs of the instrument sight. With the site on the right spot, zero set the instrument.
• To foresight points, simply loosen the motion and site the next point of interest. Once the foresight is in view, adjust the horizontal and vertical motions accordingly to the center of the prism.
• At this point you can take a shot or location fix which records horizontal distance, vertical difference, horizontal angle from the reference backsight (beginning at 0í00í00), and the vertical angle. These records may be collected in a field book (see below), or in a data collector that may be directly interfaced with a computer for download.
• Depending on the accuracy and the field conditions (i.e.-melting snow), re-level the tripod and re-zero the instrument to the same reference backsight.

The diagram below shows how the field notebook should be set up to record data:

Date:
Location:
Party:
Weather:

HI =
 

Data Collector Protocol

 The Hewlett Packard 48 series was designed to directly interface with various total station models to efficiently record data. A ram card is inserted in the back of the "48" specific to surveying applications. The "48" is interfaced to the total station by a connector cord. The proper setup and interface with the "48" will enable faster data collection in the field and greater speed and accuracy with post field calculations. The "48" has the ability to do many things including inversing between points, rotating entire jobs to the correct azimuth, and setting points to be located or staked out. The "48" surveying card allows coordinates to be calculated in the computer. Inversing between two points will give a bearing from point A to point B, a horizontal distance, and a vertical distance. The "48" is capable of many tasks that will not be discussed in this limited field surveying section.

Hewlett Packard 48 Set up for Data Collection

• First turn the unit on. The power key is in the bottom left corner of button pad. To turn the unit off, use the green hot key and then press the on key. The green and purple hot keys will allow for the commands above each key to be carried out.
• To set up a job, first select the open/edit a job key by hitting ëGí. Push ëGí again to create a new job.
• In the ënew jobí screen put in your job name by pressing the alpha key, type the name, and then press the alpha key again to relock that line. It is necessary to use the alpha key for text in both the job set up screen and when editing coordinates. If you are only concerned with point locations relative to each other and not on a real world coordinate system, accept the default northing, easting and elevation. If you have real coordinates then enter those so rotation is not necessary. Push the top left key labeled, ëAí which has the term CREAT above it. Enter an appropriate description and push enter.
• Exit from the job setup screen. Select option ëGí for open/edit a job. Then select ëJí for the edit coordinates option. Here you will see the first point that you created as point 1. It is necessary to have a backsight point set in your coordinate file before you may locate other points with the sideshot option. Therefore, you must enter coordinates for point 2 before you shoot it in. There are other ways to do this but this is the easiest. If the backsight point (2) is about 50 meters directly south, then you may estimate its coordinates by saying that the nothing is 4950.0 (ie ? 50 meters less north) and 5000.0 east. You want to make sure and give the point a recognizable description. Remember to use the alpha key when keying in text in the edit coordinates menu. After the correct information has been entered than you want to store the point by pushing the ëCí key directly below the store option.
• Exit from the edit coordinates menu two times until the option for ëJí traverse side shot is available. Choose that option. Next, select the ëCí key under the title back. Enter the backsight point to be 2 and put in the proper HI (height of instrument) and HR (height of rod). Push the ëAí key that will solve this setup. It is necessary to solve all new setups before taking any sideshots. Exit the screen and make sure that the point next to FS: is 2 also. You will now zero the instrumentís horizontal angle right on the backsight, and select the ëAí key which is labeled as sides directly above. At this point the data collector will get an accurate distance and elevational difference for the backsight point. You will then be prompted to overwrite the original point 2. Say yes to overwrite and store the new point 2. The data that remains from the original point 2 is only that it is directly south of point 1. Now you may begin to locate other points simply by imputing the correct HR (height of rod) and pushing the sideís key when the laser is centered on prism. It may be wise to start data collection at point 10 or 100 so that control points can be numbered sequentially. Remember to look at the coordinates in the edit coordinates menu to make sure the units make sense. It is possible that the instrument and HP48 can be in different units, and translations may occur. Make sure the data makes sense in the field.