The term mobile GIS? That's right! Just what do you call taking your data to the field to make edits and updates? Well, the popular term for this today is mobile GIS, even if some of us old-timers still insist on calling it surveying.
Way back in the early days of mobile GIS, surveyors, mapmakers and cartographers had some pretty primitive tools to work with by modern standards. The workhorses in those days were the plane table and the alidade. When the modern total station and electronic data collector were introduced, they expedited the collection of data geometrically. But there was a minor problem. The surveyor couldn't immediately see what his work looked like, or perform meaningful edits. Getting "plots" from the office and taking them to the field to "mark them up" became the standard method of checking and editing data.
The desire and need to edit data in the field with more advanced high-tech methods developed soon thereafter. However, solutions were somewhat slower to emerge. Early portable mini-computers lacked both sufficient computing and battery power to be effective. It really wasn't until the Pocket PC and Windows CE (the operating system optimized for devices that have minimal storage) came on the scene that what we now call mobile GIS became a viable tool. Mobile GIS, as described in the current jargon, is the integration of four technologies: GIS; small, light hardware; GPS; and wireless communications.
ArcPadArcPad GIS software from ESRI (Redlands, Calif.) has been around for some time, but it has been gaining popularity as mobile GIS proliferates into more and more organizations. In this column I will examine this mobile GIS software in detail.
ArcPad is designed to run on CE devices, but it runs on the desktop as well. In fact, it runs on the desktop first. Then it loads the firmware to the Windows CE device from the desktop PC using Microsoft ActiveSync. ActiveSync is the connectivity software Microsoft developed for its CE devices. And for the majority of the Palmtop world, ActiveSync gets the job done.
However, surveyors and mappers frequently have somewhat different experiences using ActiveSync. The principle reason for this is that surveyors need to connect multiple peripheral devices to the handheld units in addition to "syncing" to an office PC. Different devices often have different connection parameters (e.g., pin assignments). ActiveSync is predisposed to store and remember the last set of connection parameters it used. Switching devices often requires re-initializing ActiveSync on the CE device to reconnect it to a PC, which can be a source of frustration to users.
"Using ArcPad" is the support volume ESRI published for this product, and it is one of the company's better manuals. It comes in hard copy and PDF versions. In addition to hundreds of how-to illustrations for using ArcPad, this manual also contains a useful primer on Windows CE systems. "Using ArcPad" has a very useful Quick-Start tutorial that walks the new user through a few simple exercises that demonstrate most of ArcPad's features.
On the desktop PC, the ArcPad help files are arranged in a logical fashion. The CE version is somewhat more compact by comparison. Fortunately, ArcPad is shipped with a laminated guide called "Quick Help," which folds up and fits easily in a shirt pocket for use as a reference in the field.
Entering Data to the Map Document
The map document (.apm) is the working environment for ArcPad. This map document is somewhat homologous to the .mxd framework in ArcMap. The ArcPad terminology for map document data sets is the "layer." In ArcPad, a layer is basically a Shape file, an image file or an ArcIMS layer.* The user adds layers to a map document with the standard ESRI "+" icon.
All .apm documents must be in the same projection but not necessarily the same coordinates. For example, the basemap layers could be in NAD83 State Plane Coordinates. Your connected GPS could display in NAD83 geographic coordinates (latitude and longitude), but the position would be displayed in the correct location on the SPC layers. Got all that?
In addition to manual data entry, ArcPad supports wireless data acquisition. Data can be downloaded (as well as uploaded) using a TCP/IP connection like a wireless network, a modem or a cellular phone.
Viewing and Managing Layers
The same familiar ESRI icons control the view screen in ArcPad. "Zoom in," "Pan" and "Identify" allow the user to move about the map screen and query displayed features.
ArcPad supports .jpg, .bmp, CADRG (CAD raster maps) and MrSID (Multi Resolution Seamless Database) compressed images.
There are two ways the user can approach editing in ArcPad. He can use the "Select" tool and manually move or delete features, or use the "Select at GPS Position" tool and collect new ones.
CAD users like to use certain features of ArcPad as a GIS tool. In some ways, the editing functions work more like a CAD product than the process used by more standard desktop GIS packages. The difference, of course, is that all those notes that once covered the blank spaces on the drawing sheet now reside in the tables.
ArcPad will interface with a variety of handheld GPS receivers. The standard DB9 (nine pin) computer interface is available for most of the receivers, but a nine-pin gender changer and/or null modem is frequently needed to invert the pins to enable communication.
GPS Correct Extensions
Trimble and Thales both offer Differential GPS (DGPS) extensions for post-processing ArcPad collection data. Trimble's GPS Correct is a post-processing extension for its Geo CE line of products. The Thales GPS Differential Module is also a post-processing option. It runs on the MobileMapper CE and interfaces with ArcPad version 7.
ArcPad Application Builder is what ESRI calls a "Development Framework" for ArcPad. It allows the user to create custom forms, toolbars and scripts, many of which are "wizard" driven to streamline ArcPad's rather rudimentary data collection routines. It works similarly to the way VBA (Visual Basic for Applications) operates. And it can also be used to create extensions for ArcPad to interface more smoothly with peripheral devices.
ArcPad works fairly seamlessly with other members of the Arc family. This is very advantageous for the creation and maintenance of projects. ArcPad Tools is available for both ArcGIS 9.x and ArcView 3. ArcPad projects can be created in either platform and imported directly into ArcPad on the CE device.
File Management for Mobile Devices
When the CE device is connected to a desktop machine, it shows up in Windows Explorer as a drive named "Mobile Device." This allows the user to manage the files in the CE device in the same manner as any other drive mapped on the PC--by simply using Windows Explorer from the desktop.
"Drag and drop," however, works a bit differently. The user needs to use the copy and paste commands in the Edit menu to move files from the desktop to the mobile device or vice versa.
Going MobileTaking data into the field to make edits and updates will doubtless become more popular as hardware and software technology continues to improve. There may never be such a thing as the "perfect" vehicle for mobile GIS. But ArcPad 7 steps things up a notch.
*The ArcIMS (Arc Internet Map Server) file requires wireless (TCP/IP) network connection.