Abstract

OLE automation technology has dramatically expanded the potential market for GIS software engines and GIS data, by allowing GIS technology (such as Esri’s MapObjects) to be embedded in custom applications.
The same OLE automation technology can now be used to embed high-accuracy GPS capability in custom applications. Trimble’s Pathfinder Tools software development kit includes four OCX (Active X) controls for configuring, controlling and monitoring of GPS receivers, and to enable easy conversion of GPS coordinates and units.
Providing ease of integration without compromising GPS accuracy, Pathfinder Tools is the first OLE-based software toolkit to provide differential post-processing capability, for higher GPS accuracy. Pathfinder Tools offers sub-meter accuracy in the field, with Trimble's Pathfinder XR and XRS GPS receivers, and also works with Trimble's PCMCIA-based Pathfinder Card, allowing plug-and-play GPS integration.
The combination of MapObjects and Pathfinder Tools enables software developers and systems integrators to easily create a wide variety of powerful GPS/GIS field applications.

INTRODUCTION

The Global Positioning System (GPS) has long been a valuable tool for GIS data capture applications. Recent technological advances have made GPS more useful and more cost-effective as a data capture tool, and sophisticated systems for Mapping and GIS data capture are now offered by a number of manufacturers. Many of these systems provide superb accuracy, reliability and functionality, and are ideal for a variety of general-purpose data collection projects.

But for organisations which have already made an investment in field computing systems, the economics and ergonomics of equipping each field worker with an independent GPS system are often unattractive. For such an organisation, a far more desirable solution would be to build GPS capability into their existing hardware and software. Such a solution could maximise the value of GPS while minimising the impact on field staff and their work practices.

GPS INTEGRATION

Until recently, the only way to integrate GPS into a custom application has been to communicate directly with the GPS receiver, using either a GPS manufacturer’s proprietary protocol or an Industry Standard protocol such as the National Marine Electronics Association’s NMEA 0183. Most budding integrators chose NMEA, as it provides a large degree of GPS receiver independence, is an easily parsed ASCII format, and allows rapid embedding of GPS. However NMEA is a one-way protocol, providing no software control over the GPS receiver’s configuration or operation. NMEA also provides no ability to differentially post-process GPS data, which forces anyone looking for higher GPS accuracy to also purchase a GPS receiver with an integral or external real-time radio. This incurs additional equipment cost, and also inevitably restricts the areas where the equipment can be used, as it is difficult to guarantee 100% coverage with most real-time differential GPS services.
Interfacing with a GPS receiver using a manufacturer’s proprietary communications protocol has its own advantages and disadvantages. On one hand, it is normally possible to configure and control the receiver, and provide a far greater degree of feedback than is possible with NMEA. It may also be possible to record sufficient information to differentially post-process GPS data. On the other hand, most proprietary GPS formats are extremely complex, and are applicable to only a single GPS receiver or family of receivers. Although many systems integrators have invested countless software development hours in GPS receiver integration, the GPS industry is evolving at such speed that only a handful have ever managed to implement a reliable customised GPS interface which includes post-processing capability.

But now there’s a better way.

Trimble, the leader in GPS Solutions, has recently introduced a product that allows software developers and systems integrators to easily embed GPS into their applications. This product, called the Pathfinder Tools Software Development Kit (SDK), provides support both for integrated real-time differential GPS and also for post-processing. The enabling technology is the same software platform that’s allowing software companies to embed GIS capability: OLE automation. Trimble’s Pathfinder Tools software suite provides four ActiveX (OCX) OLE automation controls, which can be easily embedded in a 32-bit Windows application (i.e. Windows 95 and Windows NT).

PATHFINDER TOOLS

Pathfinder Tools currently consists of four ActiveX software controls:

1. The GPS Receiver Control. This manages all GPS data communications between the GPS receiver and host application, including the configuration and control of real-time differential corrections from radio beacons and satellite sources. A simulation mode provides the ability to record and ‘replay’ GPS positions for testing and demonstration purposes.
2. The Coordinate Transformer control provides easy and accurate coordinate conversion from latitude and longitude to any of over 650 published coordinate systems and zones. You can also create custom coordinate systems using Trimble’s Pathfinder Office software suite, and use these with Pathfinder Tools. In addition, you can use Pathfinder Office and Pathfinder Tools to create a ‘calibration’ of GPS data to practically any existing map or GIS database.
3. The Units Converter component simplifies the translation of angle, length, velocity, and time units and the conversion of GPS heading information from true to magnetic north.
4. The SSF Writer component saves GPS data in Trimble’s Standard Storage File (SSF) format, so that you can subsequently perform differential GPS post-processing on the data using Trimble’s Pathfinder Office™ Software. Pathfinder Office, which is included with Pathfinder Tools, provides a host of GPS data viewing, editing and processing facilities, in addition to GIS export. The ability to create and post-process SSF files can be crucial when you are collecting data in environments where the power and dependability of differential post-processing is required.

PATHFINDER TOOLS MAKES IT EASY

Building Pathfinder Tools into your application is extremely easy. Just install the Toolkit and then drag and drop the ActiveX control onto a window in your application. The control doesn’t necessarily expose any UI on this window, and the window itself doesn’t need to be displayed (it just provides the control with ‘a place to live’).

Figure 2
Drag and Drop the GPS Receiver Control

When you run your application, you must call a single method objGPSReceiver.StartTracking to start the GPS interface. You can pre-configure the GPS receiver, or can expose either the default UI or your own custom UI to configure the GPS receiver, either prior to activation or subsequently. If requested, the GPS receiver control will scan your PC's serial ports for a GPS receiver, so you don’t even have to rely on the user connecting the receiver to a specific port.
From that point onwards, you have GPS positions available to your application. It’s up to you to decide what you use these for. You can record GPS positions, use GPS to automatically pan the map, or use GPS to guide you to a specified point on the map or in your database.
Pathfinder Tools itself comprises the four ActiveX controls mentioned earlier. The toolkit also includes a set of custom utility controls providing some of the typical displays you’d expect to see in a GPS application:

• A skyplot, showing where the GPS satellites are in the sky and which ones you’re using.
• A speedometer and compass.
• A precise clock.
• An Activation Wizard for Pathfinder XRS receivers which require a user to ‘activate’ a satellite differential service before it can be used.

Figure 3
Sample Custom Controls

Applications built with Pathfinder Tools are showcased on Trimble’s web site, together with an interactive Object Diagram showing how easily you can interface to GPS using Pathfinder Tools.

WHICH GPS RECEIVERS CAN I USE WITH PATHFINDER TOOLS?

Using Pathfinder Tools, you can currently interface to three types of GPS receiver, offering a range of GPS capabilities:

1. Pathfinder XR is a 12-channel GPS receiver with an integrated 2-channel MSK Beacon DGPS receiver, which uses a single integrated GPS/MSK Beacon antenna. The convenient packaging and low power consumption make this an extremely attractive option in areas where coastal MSK Beacon coverage is available. In Europe, there are coastal beacons operating around the Baltic sea, in the North Sea, around the coasts of the UK and France. Experimental MSK beacons have been established in Spain and Portugal, and are being planned by a number of other authorities. The beauty of these beacons is that they provide GPS differential corrections free of charge to all users. The typical real-time accuracy of the Pathfinder XR is sub-meter, although this degrades slightly as you move further away from the coast. The post-processed accuracy of the Pathfinder XR is 50cm.
2. Pathfinder XRS is a 12-channel GPS receiver with two integrated DGPS receivers. The first of these is a 2-channel MSK Beacon receiver, similar to that of the Pathfinder XR. The second integrated radio receiver decodes signals from geosynchronous satellites, providing sub-meter DGPS positions virtually anywhere on earth. The satellite signals are transmitted by two different companies, Landstar and Omnistar, and are not free of charge. However there are a variety of pricing options based on the type of service you require, and satellite differential services provide a very cost-effective means of getting high accuracy without the need for your own GPS base station infrastructure. As with the Pathfinder XR, the Pathfinder XRS achieves 50cm accuracy in post-processing mode. The Pathfinder XRS is an extremely compact system, with a single receiver and a single antenna, allowing for very flexible use in a wide variety of applications.
3. Pathfinder Card is an entire 8-channel GPS receiver on a Type II PCMCIA Card. The external antenna connects directly to the Card, which can be inserted in the PCMCIA slot of any laptop, notebook or pen computer for extremely easy and cost-effective integration. Pathfinder Card achieves differential GPS accuracy of between 1 and 3 meters, either by post-processing or in real-time (through the use of an external differential GPS radio receiver).

Figure 4
Supported GPS Receivers:
The Pathfinder Card and Pathfinder XR/XRS

An application developed with Pathfinder Tools will automatically work with all three of these GPS receivers, without the need for specific coding or testing for each supported receiver. This provides considerable flexibility to the end user of an application built using Pathfinder Tools. They can operate different GPS equipment in different areas, to suit the accuracy requirements of different projects, and the DGPS availability in different areas. They can also mix and match equipment to reflect changing project requirements.

WHAT MAKES PATHFINDER TOOLS UNIQUE?

Pathfinder Tools offers substantial benefits over other methods of interfacing to GPS:

• Ease of integration. Drag and Drop ActiveX technology means you can be up and running with live GPS in your application within minutes. One of Trimble’s beta sites managed to add GPS to their (MapObjects) application, test it and deploy it within 10 hours!
• No compromise on GPS quality. Using Pathfinder Tools, you don’t have to choose between ease of integration (NMEA) and high performance (proprietary protocols). You can achieve the highest levels of DGPS accuracy, and still have constant quality assurance and total program control over the configuration and operation of the GPS receiver.
• The ability to log GPS data for subsequent post-processing, down to 0.5m accuracy with the Pathfinder XR and XRS receivers.
• Automated, high-quality transformation of GPS positions to the coordinate system of your choice. Transformation of other GPS data, such as speed, heading, time, etc to your selected units.

PATHFINDER TOOLS AND MAPOBJECTS: PERFECT PARTNERS

Pathfinder Tools and MapObjects are extremely compatible products, due to their shared reliance on OLE Automation technology. With Pathfinder Tools, it’s extremely easy to add GPS capability to an application built with MapObjects: just drag and drop!

Figure 5
Pathfinder Tools and MapObjects

If you have a solution built using MapObjects, you easily add GPS capability using Pathfinder Tools for the following kinds of applications:

• Map Panning and Tracking Applications. Add GPS positions to the MapObjects Tracking Layer; it’s designed precisely for the display of ephemeral graphical information.

• Data Capture. Record GPS data to a Shapefile or other data store. At the same time you can also record raw GPS data directly to a Trimble SSF file for subsequent post-processing, and after that for merging with the Shape data.

• Data Validation. Use GPS to ‘navigate’ to points on the map or to automatically search for the ‘nearest’ feature in the database.

CONCLUSION

It’s now very easy to combine a GIS engine such as MapObjects with a GPS engine (Pathfinder Tools), and create a custom application which knows where it is and knows about the geographic environment in which it’s operating. These software and hardware components open up a whole new range of customised GIS applications, from data capture and validation to field work-order management and vehicle or asset tracking.
OLE automation is allowing GPS to be easily embedded within custom GIS applications, without sacrificing flexibility, GPS accuracy or ease of use. As a result, GPS is making its way into many organisations, often without users being particularly aware of its presence. GPS is being used for simple tasks such as automatically panning maps (in tracking and viewer/query systems), as well as for more obvious tasks such as navigating to and mapping the location of a particular GIS feature.

REFERENCES

• Trimble Navigation Limited, 23 July 1998, "Pathfinder Tools Object Diagram", see http://www.trimble.com/gis/pft.htm. This www site also provides other information on Pathfinder Tools, including a data sheet, FAQ and a list of Pathfinder Tools developers.