GPS

Introduction

Recently I have been spending a lot of time working with GPS hardware and software. So much so that I feel it warrents its very own page where I can discuss what I have learned.

Hardware

I have only used two different GPS units, the Sony / ETAK serial GPS and the Delorm Earthmate USB GPS. I cant comment on all the other hardware out there so I would suggest checking out the GPS forum over at MP3Car for more information. There are a few things you should consider when deciding which GPS unit to buy.

Connection: I have seen them with USB, serial, or PS/2 connections. My favorite is serial so let me explain why. USB GPS units will require a driver to be used correctly.With a serial unit, no driver is required, you just plut it in and start using it. USB and serial both offer the ability to have 2-way communication with the GPS unit, while PS/2, to the best of my understanding, only provides 1 way communication. This is important when it comes to the GPS unit remembering its last location (see Location Memory). USB and PS/2 both provide power over the connection itself, serial does not. For a serial device, you will probably need a cigarette adapter or something of the sort. Windows XP has a hard time resuming USB devices after it hibernates. Typically if you hibernate, your GPS will not work at all until you restart your computer. This is not an issue with serial (and I suppose PS/2 devices).

Location Memory: Your GPS unit will lock on much faster if it has some notion of what its location was the last time it was on. To accomplish this some GPS units have a battery backup just for remembering the last location. My Sony / ETAK serial GPS had this but also had another interesting feature, the mapping software would tell the GPS unit where it should think it is. I dont know if this second method is common at all but that is one reason to want to have 2-way communication to your GPS unit.

Message Format: Recently most GPS units (all almost all GPS software) support the NMEA standard. This is way the GPS unit formats its messages. If you are thinking about buying a GPS unit that does not support this standard, consider a different unit. My Sony / ETAK for example transmitts in a proprietary format, thus the messages can only be read by the out-of-date software that came with the hardware, hence it is now useless. That being said, you can usually buy adapters that you place on the end of the serial connection that translate from your current format to NMEA. These adapters usually run about $40 so I would suggest just buying a different GPS unit.

WAAS: Some GPS units (like Delorme's Earthmate) support this feature. WAAS is a way of increasing the accuracy of the fix on your location. It trasmitts GPS signal correction data to make the information you are already getting from the GPS satelittes more accurate. Personally, I dont find my Earthmate with WAAS any more accurate than my Sony / ETAK without WAAS.

Power Consumption: If you are going to be running your unit off batteries, then you will care about this. If not, then dont even consider the power. When you put my GPS unit agains the rest of the components in my car computer, the GPS power consumption is minimal if it is even noticable.

Lock-on Time: This is a measure of how quickly the GPS unit can determine your position. This is a very important piece of information as it affects how long you will be waiting for directions once you start it up. Unfortunatly I believe the manufacturer pretty much gets to report whatever they want for this number so I dont trust the numbers, I trust what other users say the lock-on time is. Usually this time is split into hot-start, warm-start, and cold-start times. Hot start means that I already had a fix, then stopped tracking but power was maintained. Now it is being asked to track again. My Earthmate boasts a hot-start time of 3 seconds. I think the fastest I have ever seen it lock on is about 10 seconds. Cold start means the GPS has no idea where it should be (see Location memory). It seems to me that the average cold start time is about 1 to 1.5 minutes. That being said I have heard of cold starts taking 20 minutes. Warm starts is when the GPS has an idea of where it should be but has not previously had a lock since it was powered on. Typically around .5 to 1 minute is to be expected here.

Software

I am going to assume that you are planning on using your GPS software in a car with a 7" screen. Most GPS software packages are not designed for this. They are too difficult to interact with and require too much input to see what you want. There are a few features that can make desktop type GPS software more user friendly for in-car use.

• Voice prompts
• Voice input
• Interactivity with the map area (ie touch the map to zoom in)
• Ability to resize buttons / text to make them usable for in-car touch screens
• Large directions display

There are a handful of software is designed specifically for in-car use. These typically are my favorite. Here is a breakdown of all the software I have tried