The authors investigate the benefits for the precise point positioning (PPP) ambiguity resolution technique of using the GPS L1, L2 and L5; Galileo E1, E5a, E5b and E6; and BeiDou B1, B2 and B3 measurements. Data from 17 reference stations over a period of 31 consecutive days in 2018 were used. It was found that the four-frequency Galileo combination of E1+E5a+E5b+E6 provides the lowest geometric and ambiguity variance. In a kinematic test using triple- and four-frequency GNSS measurements, the solution convergence time can be shortened by an average of 5 minutes as compared to the triple-frequency GPS-only PPP case.

We assess the time-to-first-fix (TTFF) and the ambiguity fixing rate of two PPP wide-lane ambiguity resolution (WL-AR) methods, namely the geometry-based and ionospheric-free (GB-IF) method, and the geometry-free and ionospheric-free (GF-IF) method. First, an optimal GF-IF WL linear combination is selected based on the ratio between the code and carrier phase measurement noise ( $RT$). Then, the relation between ambiguity variance and satellite geometry in the GB-IF WL-AR is investigated. Both simulated and real data from 31 GNSS stations over 37 consecutive days in 2017 were used. Numerical results show that the GF-IF WL-AR method has shorter TTFF and higher ambiguity fixing rate compared to the GB-IF method when $RT\le 150$. However, when $RT\ge 150$, the GB-IF method outperforms the GF-IF method. Depending on RT values used, 2–10 min would be required to resolve the WL ambiguities when using GNSS measurements with one second sampling rate.

This paper presents the preliminary work is a part of a research focusing on close range photogrammetry for landslide monitoring.The main objective of this paper is to present the Close Range Photogrammetry (CRP) technique, Unmanned Aerial Vehicle (UAV) will provide a platform to monitor the surface area This method was applied using the capabilities and power of Gatewing, Unmanned Aerial Vehicle (UAV) for data capturing with respect to UAV tracking conducted in UTP, Tronoh, Perak, on 15th March 2012 at 150m height. The Gatewing is designed for rapid terrain mapping with fully automated image processing. The result proves that data processing were conducted by Srecthout Software. Flight planning was carried out on site, where the areas to be observed are situated inside the UTP campus. The paper focus on final production of an orthomosaic. In conclusion, it is demonstrated that Gatewing, UAV is the best, fast and powerful mapping vehicle for close range photogrammetry application in future works. It shows highly excellent performance compared to other UAVs already established in the market today. Keywords: Unmanned Aerial Vehicle (UAV); Close Range Photogrammetry (CRP); Gatewing; orthomosaic; terrain.