Back to Basics: Quick setup with a laser plummet.
December 1, 2009
The radio crackles. “Hey, could you come over here right away and give me line on the wall forms?” a voice asks. “I’ve got 15 people waiting to pour concrete.”
When you’re faced with this request, how much time does it take you to set up over the point and provide the line? Can you do it in two minutes?
When you watch people who truly know what they're doing, it looks like an art. However, the ability to set up quickly over a point is a procedure just like any other in surveying and can easily be performed by anyone if exact steps are followed.
Any instrument with a laser plummet can be set up quickly and efficiently by following these steps.
1. Rough-set the tripod, by observation, over the point by moving the legs in or out on the ground. Hold two legs, and place the third one past the point. Move the two you are holding until the head of the tripod is approximately over the point (within a tenth or two) and horizontal.
2. Securely attach the instrument to the tripod. Turn on the laser by pressing the appropriate button on the keyboard of the laser plummet-equipped instrument.
3. Look at the point you are planning to set the instrument over, and observe where the laser dot is in relation to the point. Quickly determine which direction the laser dot needs to move to get over the point. If it is more than two tenths from the point, you may have to move the tripod closer.
4. Rotate the instrument’s leveling screws, as needed, to center the laser dot exactly on the point.
5. With the laser centered over the point, adjust the legs of the tripod up or down to center the bull’s-eye bubble on the instrument. Work with only one leg at a time.
6. Check to confirm that the laser plummet dot is still on or very close to the point.
7. Use the leveling screws to exactly center the bubble on the instrument. The process is fundamentally the same whether your instrument has a physical or electronic bubble system. Ultimately, the bubble should remain centered when the instrument is rotated about its vertical axis.
8. Check the relation of the laser plummet dot to the point. It will probably be off the point slightly.
9. Loosen the instrument attachment clamp on the tripod slightly, and while looking at the laser plummet dot, slide the instrument until it is exactly on the point. Be careful not to rotate the instrument.
10. Tighten the attachment clamp, and recheck the level.
11. Re-level and repeat, if necessary, until the instrument is exactly level and directly over the point.
12. Constantly check and confirm. You should now be exactly over the point and exactly level. That means it’s time to get to work.
Efficiency Is Key
Using a laser plummet is one of the basic procedures of surveying field operations. After reading, studying and practicing this process, you should be able to set up an instrument in about two minutes.
Keep in mind that while this article discusses and illustrates a method that many instrument users have found to work well, there is more than one way to set up an instrument quickly. Slight differences from the procedure presented here are to be expected. If your method gets an instrument set up, level, over the point and ready to measure angles in two to three minutes--then by all means, use it.