Technical Tips
by Ishara Kotiah, Senior Analyst
Introduction
ESRI’s ArcPad software is an easy-to-use, low-cost mobile mapping tool that can be integrated with your corporate GIS. ArcPad provides intuitive mapping, basic GIS query tools and GPS functionality for recording locations. ArcPad can make field data collection and verification fast, easy and accurate. ArcPad can be deployed on a range of handheld PDA devices and tablet PC’s.
A mobile computing solution for verifying assets in the field will general provide the user with relevant attributes of the asset and mapping of the location of assets and contextual themes. However, like any other situation where technology is being introduced, the question has to be asked whether the business can be efficiently served by native software out-of-the box or whether the most cost-effective solution involves customization to minimize training and support.
ArcPad Application Builder
The most successful mobile solutions involve designing a system architecture that will support the business process workflow so that the user has access to the right data at the right time and maintains appropriate corporate data holdings. ArcPad can be can be readily customised to deliver these solutions. ArcPad is customized using ArcPad Application Builder.
This document provides an overview of the technologies and skills required to customise ArcPad to develop a tailored mobile application integrated with a database. We recommend that you refer to ESRI’s website for further details about ArcPad Application Builder.
ArcPad Customisation
ArcPad development may be approached in varying degrees depending on the level of customisation required. Most ArcPad applications are developed for capturing or updating data in the field. This is a fairly straightforward process when all the attribute data is held in a shapefile. The creation of the forms is primarily a GUI driven process in which the user drags controls, for example textboxes or drop down lists onto a form.
However more often, the data that is being updated resides in external databases that may be linked to a spatial layer. To update data in an external database like a Dbase file or an Access database, you would need to create an ArcPad applet and link a VBScript file to it. The VBScript file contains the information required to link the spatial data to an external database. You need to be familiar with VBScript in order to develop ArcPad applets. VBScript is a scripting language and is released by Microsoft.
The following sections describe how you customise data-entry forms and create ArcPad applets to link to external databases
Customising Data-entry Forms:
Creating custom data entry forms for shapefiles will require editing the APL file. The APL file is an ArcPad layer definition file containing numerous properties which dictate how that layer file is displayed, any scale dependencies, labelling options etc. A data entry form is stored in this layer definition. This means that each time a feature is selected for edit in ArcPad, the form associated with that layer will be displayed. Information forms can also be defined within an APL file, eg attribute data can be formatted to display in a particular layout. Editing an APL file is ArcPad customisation in its most basic form.
APL files may be edited using ArcPad Studio, a text editing application like WordPad or an XML editor. When creating edit or information forms in APL files it is better to use ArcPad Studio as it provides a user-friendly interface for arranging form layouts, adding controls and events. However, I find it much simpler to make symbology edits in a text editor. You can copy and paste symbology definitions and modify values much more effectively, eg to create a hatch symbol for an attribute value = “critical” in which the hatch colour is black, the background colour is red and the outline is grey you would issue the following statement:
You can then copy and paste this code for other values in the layer and change the colour and hatch definitions.
Writing ArcPad Applets to Link to External Databases:
If your ArcPad application requires data to be edited outside of a layer, eg in an external database, you would need to create an ArcPad applet. An ArcPad applet has a .APA extension and contains definitions of toolbars, buttons, and forms in an ArcPad application. An APA file is usually also associated with a VBScript file with a .VBS extension. The VBScript file may contain procedures to validate your data or to perform database inserts, updates or deletes.
A tip when using ArcPad Studio: When creating drop down lists, a more flexible option is to create Dbase files with the drop down values. This means that a user can update the Dbase file without needing to edit the code itself.
Connecting to an External Database
ArcPad provides the ability to update data held in shapefiles or in external databases on the mobile device. In many cases the business data in an organisation is held separately to the spatial data with keys linking the two. There are a number of formats for storing the external data on a mobile device, eg DBASE files, Pocket Access or SQLServer CE.
If the corporate or desktop database is Microsoft Access, you can copy it to your mobile and regularly synchronise it to download corporate updates onto the mobile and/ or upload updates from the mobile to the desktop. The synchronisation can be set-up using Microsoft ActiveSynch so that it automatically occurs when the mobile is parked in the desktop cradle.
When a Microsoft Access database is copied to a mobile device, it is automatically converted to Pocket Access with a .cdb extension. Windows CE does not have any software for viewing Pocket Access databases. You need to install third party software to be able to do this. When coupled with an ArcPad applet, a VBScript file can open a connection to a Pocket Access database and navigate through the records in a table. The first item to check is whether ADOCE is installed on the device. ADOCE is an abbreviation for "Microsoft ActiveX Data Objects for the Windows CE operating system". It contains objects for connecting to and updating a database. If it is not you can download it from the MSDN site hosted by Microsoft by looking up Windows CE downloads. The next is to determine what version of ADOCE is installed. There are two versions available 3.0 and 3.1. Once you have established this you need to provide a connection string eg.
As you can see in the example VBScript, all variables are defined as variant. Line 5 in the above piece of code creates a recordset object. Line 6 opens the recordset based on the SQL expression. The numbers on the line specify the type of cursor that is opened and the type of lock placed on the data respectively. In this case a keyset cursor (1) and an optimistic lock (3).
Summary
As with all application development, it is important to have a clear understanding of what is to be achieved by the product. ArcPad development is not difficult; however it is important that tools or products are designed with the field crew and their operational practices in mind. One of the chief reasons for a product failing is if it is not developed in consultation with the end-users. At Spatial Vision, we have considerable experience in the application development path for mobile applications and can advise you and recommend an appropriate development strategy.
