The engineers use various softwares for observation processing and GPS networks, generally everyone who uses a device, he uses softwares with the same brand for the processing of it GPS processing networks by defined default parameters and models. The most outstanding issue is that, it should be understood, the application of which kinds of softwares will help us to gain the desirable accuracy and whether the accuracy of coordinate estimation is acceptable in all commercial softwares or not. In this article, we compared a series of softwares which engineers use for their data processing with powerful scientific software that meanwhile it is too hard and time consuming to learn it. We have considered accuracy and validity of scientific software, which gives acceptable results, as a baseline to see how much errors and difference is between this software and the commercial softwares, so we selected Bernese as a scientific software and LGO, Ashtech Solutions, CGO softwares as commercial softwares and we analyzed them and compared the applied models of the softwares with each other. To do so, we choose a GPS network from Tehran city and discussed it, in order to evaluate the measured accuracy for baselines and also coordinate system that after data processing, it was understood that if the polygon of a network is small, commercial softwares can be utilized with very high acceptable accuracies and even by Ephemerides Precise data, their accuracy will increase more, but if our network is more extended and bigger, there is no other choice except using scientific softwares to calculate coordinate that performs a processing by many parameters.
In the middle of 1990s, GPS inventors introduced Real-Time Kinematic (RTK) method, that by means of it, we can achieve the desirable accuracies in surveying. In this method, the user usually is in need of a reference station which is located at maximum 10 km distance, in order to determine the position with centimeter accuracy. The applications of this method account for: positioning with high accuracy for navigation systems, guiding auto-run machines, unmanned aerial vehicles, marine missions like: dredging and large-scale map’s update [
By increasingly development of GNSS satellite navigation and emergence of new companies for production of related receivers, numerous softwares have been developed for processing of these data that in the most general form, these softwares can be divided into scientific and commercial groups. Scientific softwares that mainly are prepared by universities or reliable scientific centers are programmed for utilization in precise and professional tasks. In addition, commercial softwares which are produced by those companies that produce GNSS receivers are applied for data processing of general users and engineers. Commercial softwares not only don’t have the complexity of professional and scientific softwares, they have a plain graphical and user friendly environment that it has simplified and quicken dealing with these softwares. While scientific softwares are much more complex and have specific and professional settings that make it too hard to handle them [
In this part, we will introduce various models of this scientific software and we will explain each of them briefly.
Offset model of satellite antenna phase and variation of electrical phase of receiver antenna and offset center of receiver’s antenna have many effects on PPP processing. So models with ANTEX format have been applied to delete these effects. In Bernese software, “.rel” format is used to omit these effects and in fact, rel. is the ANTEX format of Bernese software. To achieve this format, in addition of using the products of CODE, PHCCNV software can be applied that in Bernese software is prepared for conversion of ANTEX format to “.rel” format [
Like other scientific softwares, Bernese software also, uses IGS products to decrease the orbital errors of satellite and the errors of satellite clock, so Bernese software owns this ability to decrease the errors of satellite clocks and errors of satellite clock by using “.clk” and “.sp3” formats. Furthermore, to decrease the orbital errors of satellites, it can use “.sp3” and “.pre” and “.eph” formats too.
In order to omit the effect of relocation caused by ocean upload, Bernese software uses “.blq” standard suffix of these models. One of the most famous centers that gives these models is Onsala observatory. The users can refer to the website of this observatory and fill the related form to receive these models [
Earth rotation parameters are those parameters that are presented in “.eop” standard format. These parameters both are presented by IGS processing center weekly and also they are shown in two (A) and (B) Bultons by IERS. Bulton (A) includes fast earth rotation parameters that are presented daily and Bulton (B) are earth rotation parameters which are published monthly.
Satellite state space model are models which are released annually by AIUB. These models reveal satellites’ safety at different episodes and Bernese software uses these models for proving the satellites’ safety at observing time and if satellites’ safety is not proved, that satellites’ observation would be deleted from observation list [
Satellite Ephemeris models are binary files with “.eph” format. These models are presented by solar dynamics observatory, Jet Propulsion Laboratory and NASA. Up to now, three series of these models are presented in these numbers: DE100, DE200 and DE400. Bernese software uses these models to calculate the position of moon, sun and other planets.
Since, the binary format of these models are not free, Bernese software uses a tool to convert numeral format of these models into binary format of Bernese [
Bernese software applies very well-known gravity models like: GEMT3, GEM- 10N, JGM3, EGM96, TEG4, EIGEN1 and EIGEN2 [
The ocean tide models have “.tid” Suffix that most of them are prepared by space research center of Texas University. Bernese software exploits these models for calculation of variations in gravity caused by oceanic tides.
Note: in scientific softwares, we don’t have model for ionosphere and troposphere and the software itself calculates them scientifically [
As mentioned before, in scientific softwares, we don’t have any ionospheric and tropospheric errors and the software calculates them scientifically but in commercial softwares, we decrease or omit them by models. In commercial software, we tune the ionosphere error model in automatic state that if the length of network is large, L3 frequency will be used that in this condition, the ionosphere error would be deleted thoroughly but the problem of this work is that the noise is very much. But if the length of network is short, L1 + L2 frequency is used that reduces the errors.
Parameters and cases that should be set and investigated before processing by LGO software are mentioned in