The chart is plotted under the AuotoCAD2000 environment.
During the process of office plotting, a specific plotting software package is used to edit the data collected in the field and all the data are transformed into discernable format by the topographical and cadastral plotting software package CASS4.0. We can, therefore, conclude that the surveying results are accurate and reliable. The elevation difference is generally less than 0.1m, which illustrates the coordinates by RTK method and ETS is within the allowable error of this type of project. The maximum distance measurement range is 3,600 meters.Īccording to the statistical results shown in Table 1, the maximum difference of the horizontal locations among the control points is 0.36m. The model of Electronic Total Station is Nikon DTM532 – C, with an angle measurement precision of 2 seconds and distance measurement precision of 2mm+2ppm. As for the height component, China national standard datum is used. The results are listed in the following Table 1. Coordinates from GPS RTK are compared with the coordinates derived from Electronic Total Station measurements. 17 control points of Shashi river reach are used as checking points to evaluate the RTK GPS results. GPS baseline vector is processed in order to promptly check the quality of the field observation data. They are observation file (*.o) carrier phase and pseudo range observation file, navigation file (*.n), epoch parameter file and survey station information file. The office work consists of the following two parts: data edition and visualizationĪfter the field survey work, GPS data which is recorded in the receiver/or data card needs to be downloaded through Trimble proprietary software package – TGO (v1.6).įour data files will be created. During the survey process, water level at the related hydrometric station and water level observation station is recorded at the same time for a necessary check. The elevation of the underwater surveying point is therefore deduced from the water level and the water depth. The height of each cross section is derived from the ETS. The height is measured through trigonometrical leveling with ETS. The survey boat is driven along with the cross section line while the laptop computer collects coordinates and the depth of water automatically. Before the survey is carried out, the space of the measurement points needs to be established in the Hypack survey software.
Each cross section line is roughly perpendicular to the shoreline with an interval of 200 meters. The river cross-section survey data collection and recording is carried out by the laptop computer with the Hypack survey software. The echo sounder is controlled by the computer to collect water depth signals in an electronic form and then transformed into a digital form (i.e. The sounding pole of the echo sounder and the GPS rover station antenna are put in the identical horizontal position. The SDH-13D digital echo depth sounder is used to measure water depth of the points. Coordinates of the mobile station are computed using both the received GPS satellite information and the differential information from the reference station via the data link. A common set of GPS satellites are recorded at both the reference and rover stations simultaneously. GPS roving station is located in a powerboat for bathymetric survey. GPS reference stations are located at open, ashore known points so that the reception of GPS satellite signals is not potentially blocked and the data link of GPS signal transmission does not pose any problem. The cross-section interval will be set about 200 meters apart, and Trimble 5700 GPS is used to fix horizontal position. Cross-section survey of the river depends on cross-section measurement method used.