Recent advances in mobile GPS/GIS mapping technology
Independent Laser Mapping
Laser Range finders can also be used without GPS. Here you place the laser at any reference point (base map coordinates, survey points etc) and call it "ORIGIN". From this origin, you can shoot the laser to various points of interest and the distance and azimuth readings are sent to the data collector and stored. In this method the position of features are accurate to base maps and to each other. The data collected by this method will be relative data only. However, in the future when LAT/LONG positions are available for any reference or points, one can insert that value in the software and all the relative data will be converted to absolute data in LAT/LONG.
Applications
Even though the new products described have only been introduced in the past year, their use has already become very widespread in various applications, such as, environmental, geology, infrastructure, forestry, etc. This is mainly due to the portability and ease of use of the system. (See Fig 6)
Selection Considerations
GPS Receiver Selection Consideration
The most important criteria in selecting a GPS receiver is identifying the accuracy that the application requires. The receivers generally fall into 4 categories. Autonomous - 10-15 meters, 1-3 meters, submeter, and survey grade. For all but the autonomous category, you will need some way to correct the readings. The corrections can be - Post processing, Coast Guard Beacon, and Satellite based.
In the post processing option, you need to ensure that base station data is available from a nearby base station. If the Coast Guard Beacon method is chosen, one needs to identify if a beacon station is available near the site. In the satellite based option, one needs to make sure that the service is available in the area and the subscription paid for.
Data Collector Selection Consideration
The weight and size of the unit is an important factor when using these units in the field for a long time. The type of operating system (Palm O/S, Pocket PC, WINDOWS) to be used needs to be considered if integrating with other application platforms. If you require a display of a background map, it will be preferable to have a unit with a larger screen and color display. However, the color display may reduce your battery life. If the application involves use in a rough environment, the data collector selected must be ruggedized for outdoor use. Battery life is also an important factor in the selection of the data collector. The unit selected has to be compatible with the type of GPS receiver to be used.
Laser Range Finder Selection Consideration
If you need to collect large amount of data and in areas which are difficult to reach, a laser range finder will be a very helpful tool. If the work involved is in an area where magnetic fields are present, an angle encoder will be a better choice than the digital compass.
Software Selection Consideration
As certain versions of field data collection software have limited features, several factors need to be considered in selecting the right software.
The selected software should be compatible with the GPS receiver and the operating system chosen for the data collector. Some software packages do not allow you to create and edit features in the field. This restriction implies that for any changes and or additions to the data dictionary, you will have to stop the project in the field and access a PC to edit the dictionary, reload the new version of the dictionary, and restart the field project. This is a very time consuming process which can be avoided by simply selecting the software with field editing of the data dictionary capability.
Often field data projects are handled in different datums and projections, and as a result, one should choose software with capability to select various datums/projections. If laser range finders or any other external devices besides GPS are to be used, make sure that the software is compatible and raw data is converted into the proper units. It is good practice to view the quality of GPS data collected by viewing the DOP number. Hence, one should pick a software package which displays DOP values. If you need to go back to a previously located or known point, you will need the navigation capability in the software. Most often the collected data needs to be imported into a GIS. The software chosen should be able to provide a conversion routine to allow an import of GPS and Feature data into various types of GIS software, such as, ARCVIEW, MAPINFO, and AUTOCAD.
Conclusion
The availability of new technology in the GPS mapping arena has made the data collection tasks much easier and cost effective. I see this trend continuing towards lower prices and faster speeds. This will allow new and widespread use of mapping technology. However, with more options, different price ranges and easier availability of this technology, the users have to be extremely careful when planning and implementing their Mobile Mapping project.