Selecting a Mobile Device
Mobile GIS involves a variety of tasks that are performed under varying environments and conditions. No two mobile GIS applications are the same, and different people have different preferences. For example, one person may be comfortable with entering text using a pen (or stylus) and character recognition software, while another person using the same application may prefer to use a physical keyboard. Similarly, one person may be comfortable with working with map data on a quarter-VGA (Video Graphics Adapter) screen (240 x 320 pixels), while another person may prefer a larger screen.
Selecting a suitable device for mobile GIS involves a process to determine which criteria are essential, “nice to have”, or not required. There is no perfect device for mobile GIS since many criteria are mutually exclusive. For example, it is not possible to have a device with a large screen and at the same time is compact enough to fit in your pocket—unless, of course, you have large pockets!
The following factors should be considered when selecting a device that best meets the needs and requirements of your mobile GIS application.
Operating system
ArcPad runs on Windows 7, Vista, XP and Windows Mobile devices. The first factor to consider is whether the mobile GIS device needs to run Windows Mobile or a PC version of Windows.
The advantages of Windows Mobile devices are:
- More robust: Windows Mobile devices usually use solid-state technology with no moving parts—for example, flash memory for storage instead of a hard drive—and therefore tend to be more robust than PCs.
- Less power consumption due to solid-state technology and low-power processors.
- Instant on and off: Windows Mobile devices can be switched on without needing to boot up and, similarly, can be switched off without needing to be shut down. This is a significant advantage for mobile GIS tasks, which often involve switching the device off while moving to a new location.
- Portability: Windows Mobile devices are available in a variety of form factors, some of which are small enough to fit in a pocket. Windows Mobile devices also tend to weigh less than comparable tablet PCs.
- Sunlight readable displays. Most Windows Mobile devices have screens which are easily readable in outdoor conditions, including direct sunlight.
- Lower cost than PCs. However, this cost advantage can be reduced by the type of accessories needed for a mobile GIS application.
The disadvantages of Windows Mobile devices are:
- Limited operating system compared to desktop Windows. Although Windows Mobile is a powerful operating system for mobile devices, it does not have all of the capabilities, built-in tools, and applications that desktop Windows does. This can also be an advantage for situations where a simpler operating system is preferable.
- Limited number of available applications. Only a limited, but growing number of applications support Windows Mobile. In many cases applications that have been ported to Windows Mobile have less functionality on Windows Mobile than on desktop Windows. This is only a disadvantage if your mobile GIS tasks require additional applications that are not available on Windows Mobile.
- Use of RAM as the primary storage medium. Windows Mobile devices do not have a hard drive but instead use RAM for storing application programs and data and for program processing. Most Windows Mobile devices do not have the option of adding additional RAM. There is a limit, therefore, of how many applications and datasets you can store in RAM and still have sufficient RAM free for program processing. Another limitation is that RAM requires power to maintain its contents. The contents of RAM are lost if the battery is drained on the Windows Mobile device. The battery can be drained by leaving the Windows Mobile device disconnected from a power supply for long periods of time. The RAM uses small amounts of power even when the Windows Mobile device is not being used. It is therefore a good idea to always connect a Windows Mobile device to a power supply when it is not in use.
- The disadvantage of using RAM as the primary storage medium can be reduced by using a storage card for storing application programs and data—or by using built-in, nonvolatile storage when available. This limitation is applicable to older Windows Mobile devices, but not to devices running Windows Mobile 5 or higher.
For many mobile GIS tasks a tablet PC or ultra mobile PC running Windows 7, Vista or XP Tablet PC Edition may be a better choice than a Windows Mobile device. This is especially true if you require a larger screen and/or need to run additional software that does not support Windows Mobile. There are a number of hardware vendors that manufacture tablet PCs and ultra mobile PCs suitable for mobile GIS.
Cost
Your budget for each Windows Mobile device will help dictate which factors are essential. For example, ruggedized Windows Mobile devices are at least double the cost of standard Windows Mobile devices. When considering cost it is essential to consider the total cost of the mobile GIS task, including labor and replacement costs. Labor accounts for the major portion of mobile GIS costs, and therefore it is more cost effective in the long run to purchase robust, ruggedized devices, which last longer, resulting in less downtime from damaged and broken devices.
Size of device
How large or small does the mobile device need to be? Ruggedized devices are usually bulkier and heavier than non ruggedized devices. The size of the device will dictate the screen size and whether the device has a physical keyboard.
Ruggedization
Do you need a ruggedized mobile device? Ruggedized devices cost more to purchase but are more cost effective in the long run as discussed above.
Screen size and display
How large or small does the screen need to be? Some people are comfortable using a small screen, while others prefer a larger screen. Most Windows Mobile devices have quarter-VGA screens (240 x 320 pixels), while Windows XP Tablet PCs have full-VGA (640 x 480 pixels) or larger screens.
Do you need a color screen display? Some applications do not require color displays, but most GIS data requires color to distinguish the various features and details on a map. This is especially true when using image data. Some of the ruggedized mobile devices are only available with grayscale displays.
If a color screen is a requirement, then it is essential that the display be readable in sunlight since mobile GIS tasks are usually performed outdoors. It is strongly recommended that you test any potential mobile device outdoors, in both direct sunlight and shade, before purchasing the device. Most Windows Mobile devices available today use reflective thin film transistor (TFT) screen technology, which is readable in direct sunlight.
Memory and storage capacity
How much data and what type of data do you need to store and use on your Windows Mobile device? It is recommended that you store your data on a storage card, or built-in storage, and not in RAM to keep as much RAM free for processing as possible. This also ensures that data is not lost if the battery is drained on the Windows Mobile device. It is also recommended that the Windows Mobile device have at least 64 MB of RAM and preferably more, if available.
As of this writing, the maximum capacity of commonly available and affordable storage cards is as follows:
Storage Media | Maximum Capacity |
|---|---|
Compact Flash (CF) |
128 GB for flash memory |
Secured Digital (SD) |
4 GB for flash memory |
SD High Capacity (SDHC) |
32 GB for flash memory |
MiniSD |
8 GB for flash memory |
MiniSDHC |
16 GB for flash memory |
MicroSD |
8 GB for flash memory |
MicroSDHC |
16 GB for flash memory |
Integrated GPS
Do you need a GPS for your mobile GIS task? If yes, do you need a GPS that is integrated with the mobile device? Integrated GPS receivers are easier to use, especially for the novice user. Integrated GPS receivers do not require any cumbersome cables for connecting the GPS to the mobile device—although an increasing number of GPS receivers are Bluetooth enabled, which eliminates the need for cables.
Integrated Camera
Does your mobile GIS task require a digital camera for taking photographs in the field? If yes, do you need a camera that is integrated with the mobile device? The biggest advantage of an integrated camera is that the image files are automatically stored on the same device as the mobile GIS data, resulting in easier and better integration of data. Unfortunately, integrated digital cameras are currently of inferior quality compared to standalone digital cameras, especially in terms of image resolution, optical zoom, and minimum light needed for taking a photograph. However, it is quite possible that an integrated camera may meet the requirements for your mobile GIS task.
Wireless connectivity
Does your mobile GIS task require wireless connectivity? If yes, then it is recommended that you select a mobile device that has the required wireless connectivity integrated with the device.
There are a variety of wireless options available, each for a different purpose.
Bluetooth is designed for eliminating cables by wirelessly connecting mobile devices and accessories, using serial communications. Bluetooth is ideal for connecting a mobile device to a GPS receiver, laser range finder, or bar code scanner. Bluetooth is also useful for setting up a synchronization partnership between a Windows Mobile device and a desktop PC. It is important to note that Bluetooth implementation is not consistent across all manufacturers. If you need to connect multiple Bluetooth devices simultaneously you should ensure that you choose a mobile device that supports multiple Bluetooth connections.
WiFi (using either the 802.11b or 802.11g protocols) is useful for wirelessly connecting your mobile device to a local area network, or LAN. Connecting to a LAN is useful for accessing web services, downloading or uploading data, as well as for setting up a synchronization partnership between a Windows Mobile device and a desktop PC.
Wide area networks, or WANs, are used for similar purposes as LANs, however the wireless technology for connecting to WANs have a longer range than the technology for connecting to LANs. The wireless protocols for connecting to WANs include GPRS, CDMA, EV-DO, UMTS/WCDMA, and EDGE.
Expansion capability and accessories
What accessories do you need to use for your mobile GIS tasks? Your Windows Mobile device should have at least one serial port, or be Bluetooth enabled, for connecting GPS receivers and other serial input devices. Your Windows Mobile device should also have at least one expansion slot for a storage card—for example, Compact Flash or Secure Digital. Multiple expansion slots are useful when you need to use a storage card and accessory, such as a Compact Flash GPS receiver, simultaneously.
There are a variety of accessories available for Compact Flash and Secure Digital expansion slots. These accessories include flash memory, hard drives, GPS receivers, landline and wireless modems, digital phone cards, wired (Ethernet) and wireless local area network (LAN) cards (802.11b, 802.11g) Bluetooth cards, digital cameras, VGA cards, bar code scanners, and serial I/O cards.
Field testing
It is highly recommended that you test potential Windows Mobile devices under similar conditions to those expected to be encountered when performing your mobile GIS tasks to ensure that the device meets your requirements. A color display may look bright and crisp under artificial office lighting but may be almost black when viewed in direct sunlight.