 I am Mr. Seshkanth B. Gosavi, Assistant Professor, Department of Civil Engineering, Valchandar Institute of Technology, Sulapur, presenting before you the online educational resource on coordinates of points on ground using the Resection Method of Total Station. The learning outcomes of this particular online educational resource are at the end of this session, the learners will be able to measure the coordinates of points on ground using the Resection Method of Total Survey. It will also be to explain the advantages and limitations of this method. All of us are familiar with the serving instruments. Every serving instrument requires the temporary adjustments. In case of the total station also, we have already seen that we require setting up the total station at a convenient height for the server. We also require centering operation which can be done either with the help of the plumb bob or with the help of the optical plummet such that the vertical axis of the total station will be exactly above the point marked on the ground. We also require leveling. The leveling approximately can be done by using the tripod and the leveling precisely can be done by using plate level which can be adjusted by using the foot screws or the bubble can be adjusted through the digital bubble assembly also. In addition to that, in this instrument also we need the focusing and the focusing can be done by using the eyepiece focusing as well as the objective focusing. In some of the instruments, this focusing is also possible by autofocus arrangement. But more important than all these operations, one more operation is orienting the telescope of the instrument in such a way that every point on the ground will be having the position of the total station parallel. Now this is what is called as the orientation of the total station. Keeping the instrument exactly parallel to its first position at every succeeding station is what is called as the orientation that we have already studied even in case of the plane tables. There are two methods of the orientation as all of us have studied in plane table that one is that of the orientation by magnetic compass and the other one is orientation with the help of the resection method or back siting method also. In this particular case, magnetic compass is used at the first station itself. In the first station you can do it by using the magnetic compass and that orientation, that directional sense of the instrument is already understood by the instrument. I am in the angular position of different points in horizontal plane will be always in relevance to the arbitrary north picked up with the magnetic compass. The other is other possibility of orientation is with OCC backside. In this particular case we need to have another station whose coordinates are known to us and from the occupied station we are bisecting it. In these cases we require to define the coordinates of occupied station on our own. However, there is one more method which is required when we are shifting the instrument from the first station to every subsequent location or maybe we are extending the work by setting the instrument or the total station at a new location from where we can extend our work such that at that station the data of the previous station should be available. That is called as the resection. Resection is determination of the coordinate of occupied station of the instrument with the help of minimum two stations whose data is already available into our microprocessor. What are the differences or the advantages disadvantages in case of the conventional method and the resection method or initial setup position of the instrument and extended one. In both the cases we are trying to define the coordinates of occupied station and thereafter we are trying to bisect rest of the station whose coordinates we require. On the left hand side you can see it is initial setup. So the method of orientation of the total station is done at the initial setup itself. It may be with the help of the magnetic compass or it may be with the help of the OC-CBS setup. In addition to that on the left hand side you can also see that there is a manual feed of the coordinates of the occupied station. What are the coordinates of occupied station that we are supposed to define normally those are northing, easting and we also require the zenith distance or that is called as altitude. While on the right hand side if you will see it is extended work that means the initial work has been done earlier somewhere and now we want to set up the instrument at the subsequent location from where we are going to continue the new work that we intend to do has to have the perfect connectivity with the previous work done from the initial setup and therefore we require some previously worked out data into the instrument and their locations should also be accessible from the new stations. This is called as the resection method of the plane table. The previous data should be available and the suitability of the resection method is it is suitable for the extended work. There are more chances of errors in the resection method and therefore one has to be very very cautious while working at the extended position. There can be some acceptable error which will be informed to you right in the beginning by the instrument in the resection method and if you will accept that error then you can proceed further. Here it is recommended that the accepted error should be very very cautiously chosen. The already I told you that the resection method is defined as the determination of the coordinates of the occupied station with the help of some earlier data which is available into the instrument of some other stations which are already available into the data as well as onto the field. All of us are familiar with the total station. It is also required to be set up onto a tripod and vertically below that the occupied station will be there. In some of the cases these coordinates of the occupied station are predefined like in the first instrument position while in other cases what we require is to find out its coordinate with reference to some other points which are previously already bisected from the previous station or the initial station. As you can see in this particular sketch over here we were having a refractor and this refractor can be placed near that pole or near that particular concrete components and with the help of these we can of course get the coordinates of those station from the initial station and from the new station also these particular points can be bisected by keeping prism or the target on their locations. As I said in the initial setup their coordinates are already known that means that has already been recorded into the memory of the instrument. What is done in the extended work is from the extended station we will look back to the station we will revoke their data and we will try and ask instrument to verify whether the OCC coordinates are matching with the new station with reference to these two stations or not. All of us are familiar that we can have a drawback and adapter with the prism also and this particular assembly is specifically designed for the resection method of plane table survey. If you would fix up the prism above a rod then there are chances that you may lose the verticality of the instrument and therefore you may require more time in correcting the position of the prism exactly above the same point which was previously bisected. Here pin point accuracy is needed I mean you will have to be very very accurate maybe less than 5 mm should be the error in holding the prism at the same point. In the initial setup some prisms were held maybe near that pole or near that concrete pillars or walls you have to hold it exactly at those points. Now what are the steps in resection method? This is normally done not by the standard measurement but with the software. So as usual you carry out temporary adjustments go to the onboard program software such as Topser with Topcon instrument Topser is there with Sokia or with Pentax or with Trimble some other software will be available. Create new file and give file name this is typically I am telling about the window based instrument even in case of the DOS based instrument you need to create a new file and give it a name. Go to the functions or program and select resection. You can go for the fourth step wherein you will have to enter input data such as name of occupied station, height of instrument and height of target. This can be measured with the help of the steel tape with 1 mm accuracy. Select two stations which are previously bisected from the initial instrument station. Hold the prism on them, bisect each of the station from the previous data that means we will be revoking that data and select the function observations. Keep the target on station whose coordinates are known and bisect and give input information. Repeat this till errors shown by the instruments are acceptable to us. As I said it has to be less than 5 mm so angular accuracy will be more in that particular case. It will return the coordinates of occupied station. Once those are known to us you can proceed further with the remaining steps of the total station survey wherein we can take the observations by holding the refractor at each subsequent location. Please pause the video for a while and answer following questions. Minimum how many stations should be available in previous data for resection method? Solution is minimum two stations should be needed for resection method. I have referred serving for engineers by Oran and Pee price and elementary serving by Gelani and Wolf. Thank you very much one and all.