Emulate GPS or a serial device

Question

Is it possible to get location data out of Google Gears, Google Gelocation API or any other web location API (such as Fire Eagle) in such a format that it appears to other software as a GPS device?

It occured to me reading these answers to my question regarding WiFi location finding, on Super User, that if I could emulate a GPS unit, many of these web services could act as a 'poor-mans' GPS to otherwise less useful software that requires it.

Is GPSD an option?

Preferably OSX & Python, but I would be interested in any implementation.

Deemphasize

In the absence of exact Python solutions to my question, I have started the following Project on Google Code, where I will copy the information / code I find: code.google.com/p/python-virtualgps – Deemphasize

GPSD have moved to a new location: savannah.nongnu.org/projects/gpsd – Whistling

Answer 1

There is a very similar thread on a Python mailinglist that mentions Windows virtual COM ports and discusses Unix's pseudo-tty capabilities. If the app(s) you want to use let you type in a specific tty device file, this may be the easiest route. (Short of asking the authors to provide a plugin API for what you're trying to do, or buying yourself a $20 bluetooth GPS mouse.)

Are you using OS X?

There is a project macosxvirtualserialport on Google code that provides a graphical wrapper around some of the features of a utility called socat. I'd recommend taking a look at socat if you see potential in the pseudo-tty route. I believe you could use socat to link a pipe from a Python program to a pseudo-tty.

Most native Mac apps will be querying IOServiceMatching for a device with kIOSerialBSDRS232Type, and I doubt that a pseudo-tty will show up as an IOKit service.

In this case, unless you can find a project that has already implemented such a thing, you will need to implement a driver as described in this How to create virtual COM port thread. If you're going to the trouble of create a device driver, you would want to base it on IOKit because of that likely IOServiceMatching query. You can find the Apple16X50Serial project mentioned in that post at the top of Apple's open source code list (go to the main page and pick an older OS release if you want to target something pre-10.6).

If your app is most useful with realtime data (e.g. the RouteBuddy app mentioned in the Python mailinglist thread can log current positions) then you will want to fetch updates from your web sources (hopefully they support long-polling) and convert them to basic NMEA RMC sentences. You do not want to do this from inside your driver code. Instead, divide your work up into kernel-land and user-land pieces that can communicate, and put as little of the code as possible into the kernel part.

If you want to let apps both read and write to these web services, your best bet would probably be to simulate a Garmin device. Garmin has more-or-less documented their protocol in the IntfSpec.pdf file included with their Device Interface SDK. Again, you'd want to split as much as you could into user-space code.

I was unable to find a project or utility that implements the kernel side of an IOKit-based virtual serial interface, but I'd be surprised if there wasn't one hiding somewhere out there. Unfortunately, most of the answers I found to that question were like this, with the developer being told to get busy writing a kext.

Weariful

Some really useful stuff there, thanks. I am indeed using OSX (added detail to original question). – Deemphasize

A $20 gps mouse is a good point (and a great 'poor-mans gps!), but my overall aim is to provide a virtual GPS 'data stream' from non-GPS web API's. – Deemphasize

As an aside, I really hadn't realised how cheap GPS dongles are now: amazon.co.uk/s/… – Deemphasize

Answer 2

I'm not exactly sure how to accomplish what you're asking, but I may be able to lend some insight as to how you might begin to get it done. So here goes:

A GPS device shows up to most systems as nothing more than a serial device -- a.k.a. a COM port if you're dealing with Windows, /dev/ttySx if you're in *nix. By definition, a serial port's specific duty is to stream data across a bus, one block at a time. So, it would then follow logically that if you want to emulate the presence of a GPS device, you should gather the data you're consuming and put it into a stream that somehow acts like an active serial port.

There are, however, some complications you might want to consider:

• Most GPS devices don't just send out location data; there's also information on satellite locations, fix quality, bearing, and so on. Then again, nobody's made any rules saying you have to make all that data available. There's probably more to this, but I'll admit that I need to do more research in this area myself.
• I'm not sure how fast you can receive data when dealing with Google Latitude, etc., but any delays in receiving would definitely result in visible pauses in your "serial port"'s data stream. Again, this may not be as big a complication as it seems, because GPS devices are known to "burst" data across the bus anyway, but I'd definitely keep an eye on that. You want to make sure there's always a surplus of data coming across, not a shortage.

Along the way you'll also have to transform the coordinates you receive into valid GPS sentences, as well. You can find specifications for those, but I would definitely make friends with the NMEA standard -- even though it is a flawed standard, it's the one everyone seems to agree on anyway.

Hope this helped you, at least a little bit. Are there anymore details specific to your problem that you think could be useful in answering this question?

Encephalic

Also note: I'm not too familiar with GPSD, but yes, it may be an option for you if I've understood you correctly, given what you've mentioned in your question. – Encephalic

Some good detail there - are there any existing libraries / products that can emulate the serial ports? – Deemphasize

Added some more detail re. my aims to the original question. – Deemphasize

NMEA-speaking GPS devices generally produce whatever messages they want, whenever they want, and say nothing when they have no info, and software pretty much has to cope with that. A GGA / GLL / RMC sentence triplet every few seconds (with a couple fields like "number of satellites used" faked up) would probably fool most software. – Arruda

Matt, I marked Nate's question as the answer as it gave a lot more detail, but I wouldn't of got on to that course of questioning without your original reply - thanks :) – Deemphasize

I have no problem with that. It appears he is much more knowledgeable on the subject, and I even learned a few things from his answer. :-) – Encephalic

Answer 3

Take a look to Franson GPS Gate which allows you to connect to Google Earth among other things (like simulating GPS and so on). Is windows only though but I think you could get some useful ideas from it.

Sleight

This is exactly the sort of thing I'm looking for, but ideally the source code that accomplishes it. Good stuff though :) – Deemphasize

Answer 4

I haven't looked into it very much, but have you considered using Skyhook's SDK? It might provide you with some of what you are looking for. It's available for every major desktop and mobile OS.

Assignment

Skyhook has a 'virtual' GPS (downloadable after you register), similar to Franson GPS gate but it's Windows/mobile only – Deemphasize