Topcon Total Station

Instructions for Forest Mapping

Written by Barry Argo
Most Recent Revision: December 1995

Total Station equipment:

  • The GTS-300 instrument
    1) Handle/ battery
    2) Measurement module
    3) Tri-bract base
     
  • CMT MCII datalogger and signal cable
  • Prism and Target pole
  • Data retrieval software and peripherals

  Other equipment needed:

  • plumb bob
  • meter tape
  • folding meter stick
  • compass/clinometer
  • tiny flat screwdriver
  • survey pins
  • flag stakes and Sharpie
  • two-way radios
  • survey field book
  • program instruction book

Precautions:

1) Sun - NEVER point the instrument at direct sunlight, which could damage components. More importantly, it WILL instantly and permanently blind you!

2) Rain - NEVER let the instrument get wet; not a drop; it WILL destroy electronics!

3) Fine-focus adjustment knobs; keep unlocked when not actually taking a measurement, and especially during transport, or fine gears can be stripped.

4) The Horizontal Circle Ring at the bottom of the instrument holds the coordinate plate from which measurements are calculated. This ring MUST remain stationary while instrument is in use. The black knob with white dot clamps the ring into place and sometimes becomes loose during transport. Be sure this knob is tightened securely!

Setup:

The Total station requires a known instrument point and backsite from which to generate coordinates. An arbitrary instrument point may be chosen and a backsight established with a compass and meter tape.

  1. tripod over point
    Set up tripod over instrument point, about chest high with one leg upslope.

  2. attach instrument
    Carefully set instrument on tripod base and secure with yellow-handled screw attachment.

  3. remove inst. from tribract
    With small screwdriver, loosen screw to unlock tribract fixing lever, and carefully remove instrument from tribract.

  4. attach plumb bob
    Attach plumbbob to clip under tripod and adjust tripod plumb over point with base plate leveled by eye.

    Adjust legs to get bubble off wall of level.

    Carefully punch in legs by standing on footplate.

  5. readjust to get bob over point
    Readjust legs to get bubble off wall of level. Plumbbob should still be close to survey pin.

    Carefully reattach instrument to tribract and lock securely.

    Make sure the coordinate plate knob is tight!

  6. optical plummet view
    Look through optical plummet telescope on side of instrument, and focus field and retical.

    Survey pin in center of sight is ideal; outside of center but in view is usually acceptable.

    Tribact can be moved slightly horizontally to adjust view. If pin is still not in view a slight adjustment of tripod legs may correct. Otherwise tripod must be reset.

  7. fine level
    The three screws on the tribract adjust the fine leveling of the instrument. Always use this method when fine leveling: Put both thumbs on screw facing you and hold stationary. Adjust other two screws with middle fingers, turning in opposite directions (as if they were gear cogs) to level in one plane, then turn only the knob that thumbs are to level in the other plane. Use this method first to center bubble in circular level. Next, turn instrument so that plate level above display is in line with thumbs, and SLOWLY adjust two screws to center bubble in plate level. Then rotate instrument 90 degrees and adjust remaining screw to level in that plane.

    The instrument should now be level and ready to turn on. From this point throughout measurements be EXTREMELY careful not bump or step to closely to tripod legs or instrument will be through out of level, and measurements compromised.

    Turn instrument on by pressing green POWER button once, and display should light. Be sure that vertical and horizontal motion clamps (fine focus locks) are loose, and rotate vertically and horizontally several complete turns to clear instrument memory.

  8. prism set
    Set up prism rod on backsight point. When first setting up on a previously unsurveyed sight, this will be an arbitrarily chosen point, usually about 10 meters from instrument point in a cardinal direction (e.g. magnetic north). The instrument MUST have this initial backsight from which to calculate subsequent measurements. A pin is set at this point using compass to sight directly across the initial instrument point , a the tape measure is used to find approximate slope distance from instrument to backsight point. The person in charge of the prism rod should push tip of rod into ground and hold level as possible.
     
    The person operating the instrument then must locate the base of the prism rod.

  9. sight through collimator
    The small black tube at the top of the instrument is called a "collimator" and allows for rough sighting. Look through the tube until you see an upward-pointing triangle superimposed on field of view. Be sure that adjusting knobs are loose, and move instrument viewer until tip of arrow is on top of rod base.

  10. focus on base of rod
    Lock vertical and horizontal fine adjust knobs and look through viewfinder. Adjust focus ring until rod comes into focus. Adjust reticle ring until crosshairs come into focus. Fine focus screws can then be adjusted until crosshairs are directly on intersection of ground level and bas of rod.

  11. zero set
    With rod level and instrument focused, press the "zero set " button TWICE. The instrument will now take all measure from this location as the zero bearing.

     Now loosen adjust knobs and focus on the prism itself.

  12. plug in datalogger; turn on
    Connect the datalogger to the instrument using the connector cable with telephone type jack at datalogger end to "signal" jack on instrument. Then turn on datalogger and scroll through menu to set system options according to table1. Datalogger operations are detailed in C&G software manual.

    Choose "collect raw data" option from main menu. Enter job and file data.

    Initial instrument point will be "1"; backsight point will be "2"

    Determine instrument height by measuring folding rule from ground at survey pin to hash mark on side of instrument.

    BEFORE entering "rod height" be sure that instrument is focused on level backsight rod; as soon as this is entered, machine will shoot the backsight point. Default rod height with tip in ground is 1.36m. (center of prism to tip is 1.40m.)

    Instrument should give two beeps when it begins shooting and two plus three when it has successfully collected the data point.

    IMMEDIATELY RECORD information from backsight point data, specifically horizontal difference and vertical difference, as this will be needed to reduce data to coordinate file.

 

Now you can begin taking frontsight points (which will default to #3) by following the same procedure for focusing instrument and entering data. Frontsight points will not automatically shoot after rod height is entered, for another set of options are available.

 

If using the "offset option" (if trying to locate the center of a tree for example) the instrument will first shoot distance and elevation to prism (tip on ground next to tree) , and will then prompt for angle (adjust crosshairs to center of tree) and measurement will be adjusted internally.

 

Make as many measurement s as possible from a single instrument point, including putting down marker at places that will make good sight to reset instrument to continue measurements (New inst. points).

 

To move to a new instrument point, instead of taking another frontsight, escape to "Inst. point" prompt. turn off datalogger and instrument and move to new sight, following the same procedures for setup leveling, etc.

 

Enter the correct new instrument point (which is one of your previous frontsights) and use the previous instrument point as your new backsight point. (Remember to be focused and leveled before entering rod height!

 

When finished surveying an area, carefully repack all of the equipment, and refer to manual for reduction and retrieval of data.