Low cost optimized GNSS application
Oct 2012 | No Comment
Today global navigation systems have become a part of our everyday life. It is part of many useful things and assisted people in many ways. It is part of the marine, aircraft and traffic issues – from private user up to logistic cooperation. Also it is used in agricultural companies for precise farming as well as for information systems in all kind of tasks like geology, archeology, hydrology and a lot more. In the sector of engineering, it supports and guides the construction machines. Diverse scientific experiments and duties utilize GPS as part of their time measuring systems. In the field of survey, the exploit broadness is also widely spread.
The main motivation is to provide a solution for engineering professionals but with a mass market-based Android application platform. So, combining simplicity in handling with object orientated databases – where targets can be addressed and edited. It can be used by people without special surveyor education but produces outcomes that can further be used in high end solutions. A qualified post processing is possible any time.
A large part of the world doesn`t have the infrastructure for bi-directional online services for high precision GNSS and also lack of money for cost intensive two frequency devices. In conclusion, we try to use the possibilities that are available at the time to raise the precision of low cost GNSS devices. The fields of use are the rail and road maintenance (infrastructure and building sites) as well as the power supply infrastructure.
At the time, we combine tablet PC’s that have the application and already have an internal GPS chip (in some cases an AGPS) or for higher precision OEM GPS receiver via Bluetooth (see figure 2).
So GPS and GLONASS satellites are used in combination and additionally the SBAS service from the geostationary satellites. In conjunction, the signals can suffice to raise the precision up to 1.5m accuracy and lower. This is an adequate resolution for supervising in the field and detecting data.
GNSS is the term for a global navigation satellite system that consists of several satellites (~ 30) which transmit their position and time. With the combination of the signals (min. 4 satellites), a receiver could identify its own position through intersection methods. There are some GNSS in use and they partly transmit on the same frequency (see figure 3).
There are GPS (USA), GLONASS (Russia), Compass (BeiDou) and Galileo (Europe – under construction). Each global navigation satellite system consists of 24 to 34 satellites in altitudes of 19,000 km till 25,000 km. The European system – Galileo, the only system that`s not under military control, is still under construction and competes with china`s system – Compass for the same frequency channels. The channels were configured for thin bandwidth, so that important military channels are not overlaid.
SBAS is an additional system that makes use of geostationary satellites which have a transponder on board that broadcast on the same frequency channel as GPS correction signals for improving the positioning. The additional SBAS system with geostationary satellites for Europe is called EGNOS. There are several SBAS systems in use and intended, which are dispersed over the world and continents (see figure 4). There is the WAAS (Wide Area Augmentation System) from the United States, the MSAS (Multi-functional Satellite Augmentation System) from Japan, the proposed GAGAN (GPS-aided geo augmented navigation) from India, the proposed SDCM (System for Differential Correction and Monitoring) from Russia as well as some commercial solutions.
The differential navigation system EGNOS (for Europe) transmits the corrections of the GPS signals via 3 geostationary satellites (120,124,126) at the time. In near future, it should be amplified with two additional satellites. The data are used for safety in aviation. When the position accuracy exceeds a marginal value of about 20 m horizontal/40 m vertical radius, a warning signal is transmitted after 6 seconds. So the user knows that there is a problem with the signals and the data are too inexact for using GPS alone. The gratis correction data are not so dense like the paid ones. Also there are several proposals with costs from the regional government authorities. For Germany, it is SAPOS where correction data for high accuracy is sent via radio or internet (also mobile communication). The adequate service for central and eastern Europe is called EUPOS. This is a special kind of Ground Based Augmentation System (GBAS) with more than 1,000 permanent stations between 6° east and the Ural Mountain (www.eupos.org). So the correction data could be processed in real-time or retrospectively. The IGS (International GNSS Service) has stations and service centers around the world that provides correction data for the time specifications and maps of the ionosphere. GIGOS service available correction data from IGS:
– The satellite ephemerides for GPS and GLONASS,
– earth rotation parameters
– IGS tracking station coordinates and speed measurements
– GPS and IGS monitoring stations and their time information
– The tropospheric zenith path delay
– Global ionospheric maps (www.igs.org/components/prods.html)
The IGS centers generate and provide accurate GPS and GLONASS products and facilitate support. The IGS service portal is called GGOS. GGOS integrates different geodetic techniques, different models and different approaches in order to ensure a long-term, precise monitoring of the geodetic observables.
The benefit of low cost GNSS applications is brilliantly described and taken in focus in the targets and working groups of UNOOSA. The United Nations Office for Outer Space Affairs (UNOOSA) is the United Nation’s office responsible for promoting international cooperation in the peaceful use of outer space. UNOOSA serves as the secretariat for the General Assembly’s only committee dealing exclusively with international cooperation in the peaceful use of outer space (www.UNOOOSA unvienna.org). UNOOSA is the current secretariat of the International Committee on Global Navigation Satellite Systems (ICG). The current and future development planned GNSS and SBAS systems are described in one of the main ICG publications.
Tablet-PC with GNSSApplication
The application could be downloaded from the technet-rail server for the German Railway. There is an online and an offl ine version. The installation is carried out on the SD card of the device. Track geometry data and points of interest and infrastructure facilities are stored on the SD card too.
Subsequently, the data can be read out and committed to other computers for further editing or for documentation. It’s also possible to synchronize data via Internet or transferred to experts. The app is working on the android system (minimum version 3 – “Honeycomb”). The SD card space should be minimum 32 GB. When the app starts, the dataset is loaded and the internal GPS is on reception. Over the Bluetooth connection, an external GPS receiver can be connected. This has a tremendous infl uence in raising the accuracy of the positioning without using any mobile GPRS /3G /4G or internet services.
The tablet shows your position in an information system background, so you can retrieve information and determine points of engineering maintenance interest (rail or electric wire faults). The system has a layered structure on which several datasets can be imported. Data of objects like bridges, tunnel, crossings, rail switches or nature protection areas are available as well as information about the whole rail net like the track numbers and the chainage.
Despite this, there is always the coordinates shown in UTM and as geographic coordinates. There can be hand out PDFs at any time to present and transfer an issue to colleagues. The elements (bridges, tunnel…) are implemented as editable objects and can be additionally fitted with comments or technical data. Just as well, there can be exported geotiffs or tiffs. In the background, there is diverse map material (scalable) achievable for the different user tasks. The infrastructure plans from the German Deutsche Bahn AG (ivl plan) shows the rail environment and counts as special maps, but there were also open source data implemented like WMS (web map service), TMS (tile map service) or some free digital orthophotos (DOP40) from the German bureau of cartography and geodesy. They cover the state “Nordrhein-Westfalen” in 40 cm ground resolution. In principle, every user can load or buy map material for their issues from several services and call them up via internet. The interface for implementing the data is already there.
The position of the user is shown in the middle of the monitor as standard. In the upper menu console the coordinates are shown as well as information to the track the user is on. So there is shown the nearest track number and the chainage at this position. It also classified the rails in main or stationary rails and additionally could replay directional if there were nature protection areas to estimate. The tracked data can be exported to just save or use it for documentation purposes or for further processing.
The High precision corridors are a combination of raster and vector data of the tracks and the track vicinity infrastructure. All this are stored on the SD card. The navigation tool allows the precise navigation based on geo position, track number and railway station ID.
If the online use is not possible, the background for the geo position is the raster data of the railway cadaster. Additional markers can be loaded for representing clearance restrictions.
– Diverse basis layer
– IVL drawings (infrastructure maps of the Deutsche Bahn AG)
– Information of main and rail station tracks
– Information of chainage
– Search function to navigate to stations, tracks with chainage or coordinates
– Display position with marker
– Display clearance restrictions
– Display environment protected areas
– Set points of interest
The Android unit with application and internal GNNS chip. Diverse information layer are also offl ine accessible because they are stored on the SD Card. An OEM GNSS (GPS/GLONASS L1) sensor plugged on via Bluetooth.
The app is useful as a low cost GNSS solution for investigation, capturing measurements in real time and simple for field evaluation. Further analyzing subsequently on high end software is feasible. The app can be modified for other duties so it could be convenient for diverse disciplines. At the time, it is on the stadium of a pilot project and has to extend in its features.
IGS (www.igs.org/ components/prods.html)
http://www.ggos-portal.org/ lang_en/GGOS-Portal/EN/GGOSProducts/ GGOS-Products.html
SAPOS article and websites (www.sapos.de)
UN OOSA (www.oosa.unvienna.org/)
ICG_ebook.pdf – Current and Planned Global and Regional Navigation Satellite
Systems and Satellite-based Augmentations Systems