DIGITALNA ARHIVA ŠUMARSKOG LISTA
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intersecting directions regarding to traditional methodology, distances are also measured in this study to enhance control on measurements. This also increases the reliability of the observations and enhancement of the accuracy for point positing to be determined.
Figure 4 also illustrates the measurement sketch. Although one triangle is enough to solve the point coordinates, namely K, located under the forested area (forest condition), the model is built for solving the problem using two triangles, not only to control the measurements surveyed at field site but also to control the coordinates of the points, namely N3, N4 and K, whose directions or distances are measured. The above-mentioned angular variables seen in Figure 3 were calculated for each triangle using the following expressions (Eq.1 and Eq.2). The formulas below formulas were generated according to Triangle 1:
Eq.1 is the cosine rule for finding bearing angles and Eq.2 is the formula of finding the azimuth, which is defined as a horizontal angle measured clockwise from the north base line. Here, a is one of the interior angles of Triangle-1. S1, S2 and S3 indicate measured horizontal distances of the Triangle-1. t is the azimuth angle. DY and DX are departure and latitude values, which are Y and X components of a line in a rectangular grid system, respectively.
Table 1 shows the coordinates calculation procedure of point K. The formulation has been given for triangle I and III.
3.3 Model Validation – Valjanost modela
In this study, the precision of GNSS positioning was calculated using the following equation:
Where indicates the precision of GNSS positioning; and indicate the differences of positional errors along the x and y axes, respectively.
4. RESEARCH RESULTS
4.1 Surveys at Field Site – Terensko snimanje
To supply the available condition in this computation strategy, visibility between points N3 – K, and N4 – K should be provided. The terrestrial surveys conducted with total station presented in Table 2 were performed to obtain the horizontal directions, vertical directions and horizontal lengths.
GNSS surveys were conducted at N1 and N2 simultaneously. Stations N1 and N2 illustrated in Fig.4 were surveyed by RTK GNSS method by using İSKİ-CORS network (Fig.2), and corrections were made via VRS mode, then the coordinates of these points were determined. The Position dilution of precision (PDOP) values for N1 and N2 are 2.089 and 1.615, the horizontal RMS (root mean square) and vertical RMS values are 7 mm and 14 mm, and 9 mm and 18 mm, respectively. The visible satellite numbers for N1 and N2 are of total 12 with 5 GPS+7 GLONASS, of total 14 with 6 GPS + 8 GLONASS, respectively. The elevation mask is 10 degree, and record interval is 10 seconds. The provided coordinates depending on these survey situations are computed as shown in Table 3.
A 3 hour-static GNSS survey at point K (under the forested area, see Fig. 6) was computed by using ISKI-CORS reference stations PALA and KCEK (approx. 10 km far away from the