A tachymeters is a theodolite with integrated device for distance measuring. A tachymeter is also called a total station. In the 80s, theodolites were expanded with a distance measuring attachments and thus became tachymeters. From 1990 on, this attachment standard in all total stations or tachymeters.. Measured results (vertical and horizontal angle and slope distance) were recorded by hand well into the 90s. During the middle of the decade, this raw data was then saved and converted into 3-D coordinates (x, y, z). By now, records are matched directly with a digital model. Users take advantage of a digital 3-D model (*.dxf, *.dwg, *.3dm; ...) and all measured results and logged data are directly incorporated into the 3-D model.

GLM Lasermeßtechnik distinguishes between two types of total stations:

  • motorized and non-motorized instruments. They are characterized by the following differences:
  • Non-motorized instruments usually require two persons to operate. Person A stands next to the instrument and uses the eyepiece (telescope) to focus the instrument on the target (marked target). The slope distance and the two angles are then measured to the target point and converted into 3-D coordinates. The second person then removes the target mark off the target and takes it to the next destination. If a point is to be staked out (transferred to the location), person A provides person B with 3-D correction values (Ay, Ax, Az) after each measurement. Person B then shifts the target mark as indicated by the corrected values, another measurement is triggered by person A, and person B is again provided with correction data. This is repeated until the [ACTUAL] point is within the stakeout tolerance.
  • For motorized instruments, no one is required to be at the tachymeter. Only one person is needed. The instrument tracks the target and target mark automatically and is controlled with a digital data carrier (electronic field book, handheld PC). The user can also allow the total station to lead him or her to a specific point (similar as a car's navigation system) because the 3-D correction data are displayed on the mobile or handheld data carrier in real time.

For distance measurements, different types of measuring technologies are available (pulse method and phase comparison method). All tachymeters made by Sokkia use the phase comparison method.

Different types of target markers can be used as well:

  • On a prism (reflective, SMR)
  • On a special foil and
  • Reflectorless

As already mentioned above, the software controlling the tachymeter increasingly gains in importance. Many experts are by now of the opinion that "without adequate software in a digital handheld field unit or instrument, any economical or efficient work is no longer possible."