3.3. Total Stations

This instrument is an integrated version of an electronic Theodolite and an EDM, as shown in Figure 3.6. It also has a small micro-processor, electronic data collector and storage system. A Total Station is an electronic/optical instrument used to measure sloping distance of object to the instrument, horizontal angles and vertical angles (Garg, 2021). Micro-processor in Total Station processes the collected data to compute the average of multiple angles measured, average of multiple distance measured, horizontal distance, elevation of ground, and 3-D coordinates of the observed points. These data can be stored in the system itself but each Total Station has a limited storage space. The data can be transferred to a laptop and desktop later for its processing.

A Total Station combines the functions of an electronic theodolite and an electronic distance measuring (EDM) device. It measures the angles and distances from the instrument to a target point, allowing surveyors to calculate the coordinates and elevation of that point. The integrated micro-processor helps in processing this data, averaging multiple measurements, and storing them for later use. Because the Total Station has limited internal storage, data is often transferred to larger systems for further analysis.

Think of a Total Station like a smartphone equipped with a camera and GPS. Just as your phone can take pictures of locations and record their coordinates, a Total Station measures the angles and distances to points in a survey. Like saving photos and maps on your phone for later use, the Total Station saves survey data to be used for creating maps and planning projects.

The Total Station sends out infrared waves that are reflected by the prism kept at the object. By taking measurements of the prism, the Total Station computes the prism’s coordinates as well as reduced level of the ground point. Some of the major advantages of using Total Station over the conventional surveying instruments are; saving in time, ease in working, increase in accuracy, and facility to use computer for storing, processing the data and derive the final result in a desired format (Gopi et.al., 2017).

Total Stations work by sending infrared waves toward a prism placed at the target point. When these waves hit the prism, they reflect back to the Total Station. By measuring the time it takes for the waves to travel to the prism and back, the Total Station calculates the distance to the prism. This distance, combined with angle measurements, allows the instrument to determine the target's exact coordinates on the ground. The efficiency of this system makes it faster and more accurate than traditional methods.

You can think of the Total Station's operation like a game of catch with a friend in a park. When you throw the ball (the infrared wave) at your friend (the prism), timing how long it takes for the ball to come back gives you an idea of the distance. Just as you can adjust where you throw the ball to reach your friend accurately, the Total Station adjusts its settings to accurately measure distances and angles.

Total Station consists of a distance measuring instrument (EDM), an angle measuring instrument (Theodolite) and a simple micro-processor (Figure 3.7). It is a compact instrument, and one person can easily carry it to the field from one point to another. Total Stations with different accuracy, in angle measurement and different range of measurements, are available in the market. The components of a Total Station are as follows: 1. A tripod which is used to hold the Total Station 2. A mainframe device which is used to record, calculate and even manipulate the field data. 3. Prism and prism pole/tripod which can be used to measure distances up to 6-7 km with triple prism 4. Battery is required to provide power source to the instrument.

A Total Station combines several key components: the EDM for measuring distance, a theodolite for measuring angles, and a micro-processor for data processing. This compact device is lightweight and portable, allowing surveyors to carry it easily to different field sites. It typically includes a tripod for stabilization, a mainframe to record data, and a prism, which reflects the infrared waves back to the Total Station for distance measurement. Battery power is essential for the operation of the device in field conditions.

Imagine a Total Station as a high-tech camera tripod. Just as the tripod holds your camera steady to capture perfect photos, a Total Station rests on its tripod to ensure precise measurements. The camera (EDM) snaps distance measurements, the lens (theodolite) captures angles, and the 'computer' inside (micro-processor) helps organize all that data so you can create beautiful maps and models later, just like photo editing software helps you process your photos at home.

Fix the instrument on the tripod that has been firmly kept on the ground. Fix the instrument on the tripod with the help of a given screw in tripod. Set up the instrument on the ground point. Some instruments have optical plummet which consists of a sharp laser beam and may be used for centering purpose. Levelling of the instrument approximately with the help of “bull’s eye bubble” using eye judgement. Use the standard procedure for levelling, and then correct the levelling precisely electronically. Focus the diaphragm. Fix the prism on the prism rod at a known height. Since, the prism rod is graduated so height of the prism is known. Measure the height of instrument with the help of a tape. Set up the working unit in the instrument. Enter the height of prism pole, height of instrument, coordinates of point where instrument is kept (if known), temperature and atmospheric pressure at the site (if known). Focus the prism kept at the other point. Bisect the centre of reflecting prism and with the help of appropriate functional buttons in the instrument. The measurement will be displayed on the display panel. Store all the measurements in the instrument itself. Compute the other data from measured observations. To speed up the work, more than one prism set is used the field. Various persons can set up the prisms at respective locations and observer from the same location of instrument can take observations all around. It saves lot of time in data collection.

Surveying with a Total Station involves several key steps. First, the instrument is secured onto a stable tripod. Then, it is leveled using a 'bull's eye bubble' for initial adjustments and electronic corrections. After focusing on the prism, the surveyor enters necessary parameters, including the height of the instrument and prism. Measurements are taken to determine the coordinates and elevations of points. To improve efficiency, multiple prisms can be set up at various locations, allowing the surveyor to gather data more rapidly.

Think of setting up a Total Station like preparing to play a game of darts. You need a firm and stable board (tripod) to hold the dart (Total Station) steady. You check to make sure the board is level (leveling the instrument) before trying to aim at your target (prism). Once everything is set up, you can throw darts at multiple targets quickly, similar to using several prisms around your Total Station to take measurements all at once.

Most Total Stations have a distance measuring accuracy of 2-3 mm at short ranges, which will decrease to about 4-5 mm at 1 km (Mishra, 2014). Although angles and distances can be measured and used separately, the most common applications for Total Stations occur when these are combined to define the position in control surveys. 1. Angle measurement: To measure horizontal and vertical angles, the Total Station is used with an accuracy of better than one seconds. For horizontal measurement of angles, any direction can be taken as reference. In case of vertical measurement of angles, horizontal direction is taken as reference. 2. Distance measurement: The EDM is a major part of Total Station. To measure the distance, EDM instrument of Total Station is used with an accuracy of 5-10 mm per km or better. The accuracy varies with each Total Station equipment. They are also available to be used in Robotic mode, with automatic target recognizer.

Total Stations are notably accurate in both angle and distance measurements. Angle calculations are precise to less than one second, and distance readings typically range from 5 to 10 mm of accuracy per kilometer. These two measurements, when combined, allow for precise positioning on the surveyed land. Additionally, modern Total Stations also come in robotic versions that can automatically recognize and track targets, further enhancing productivity in the field.

You can visualize the accuracy of Total Stations like a GPS in your car while navigating. Just as a GPS gives you clear turn-by-turn directions (distances) and the exact angles to turn at intersections (angles), Total Stations give surveyors precise measurements to ensure they accurately map or lay out land for new projects. In a robotic Total Station, it's like your GPS learning to predict when to reroute based on traffic, offering even smoother navigation.

There are two methods of measuring the distance; (i) With reflector and (ii) Reflectorless or prismless modes. The prism method uses a reflective prism at the measurement point, and the non-prism or reflectorless method does not require a reflective prism. Both the methods have been widely used in engineering and industrial surveying systems to measure the distances and angles automatically (Xia et al, 2006).

Total Stations can operate in two main modes: with a reflector and without a reflector (reflectorless). The reflector method requires a reflective prism placed at the target point to measure distance and angles accurately. In contrast, the reflectorless mode utilizes a laser beam to measure distances without a prism, making it ideal for challenging terrain or hazardous locations. Each method has its own applications, and it is essential to choose the right mode based on the surveying conditions.

Think of these two methods like using binoculars versus a camera zoom to see a bird in a tree. The binoculars (reflector method) give you a clear view, but you need to be close enough to the bird (the prism) to get a good shot. Using a zoom camera (reflectorless method) allows you to capture the same bird from far away without frightening it off, making it easier to get a good picture without needing to approach the subject directly.

Another advancement in Total Station is the emergence of Robotic Total Station (RTS) which is able to follow a prism horizontally and vertically through servomotor in the instrument. These RTSs are expensive as they have more sensors in the device as well as prism. These sensors make the instrument to work in robotic mode. The servomotor automatically rotates the instrument, as it communicates with an Advanced Tracking Sensor (ATS) fitted in the prism for tracking the movement of the prism (Garg, 2021).

Robotic Total Stations represent a significant technology advancement, allowing for automated tracking of prisms without the need for the surveyor to constantly adjust the instrument's position. Using servomotors and advanced sensors, these devices can automatically rotate to follow the prism's movement, making them very efficient for surveying tasks, especially in dynamic environments. Although they are more expensive due to their sophisticated technology, they significantly reduce labor costs and time in the field.

Imagine a studio camera that automatically follows an actor during a performance without the need for a camera operator. Just as the camera adjusts its angle and focus to keep the actor in the frame, a Robotic Total Station follows the moving prism, allowing one person to conduct a detailed survey as effortlessly as the camera captures the action on stage.

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