[l008com]

Are there any (free) apps that let you make maps by tracking your GPS location. Ideal something that could then be downloaded as an EPS, and imported into illustrator for turning into a real actual map? How accurate is the GPS of the iPhone. Within a few feet would be plenty for the map I'd like to draw. IF it's +/- 50 feet, that probably won't work.

I don't yet have a GPS enabled iPhone so I can't really answer this myself. But once I get one, this is one more thing I could do with it, assuming theres an app that can get the data, and let me access it.

[subego]

Is there any reason you want to do so much in the phone when you plan on having a full-blown computer in your workflow?

Seems easier to get just raw GPS data from the phone and do everything else on the computer.

[l008com]

Isn't that exactly what I'm asking for? Just some way to track a path with accurate GPS, and then export that 'line' in some format I can work with.

[subego]

You can surmise from my question there are interpretations of what you wrote which don't match what you're asking.

MotionX GPS Lite for iPhone, iPod touch, and iPad on the iTunes App Store

No EPS, but you can export the data. Free.

In general, I'd say the GPS is accurate to within 20'. I've hardly done an exhaustive analysis though, so I'd trust someone else's word over mine. Heavy GPS use is going to eat your battery too, so be forewarned.

[ghporter]

MotionX works out to be a fairly decent GIS data collection tool-as long as you don't need more accuracy than an iPhone can generate, or coverage where MotionX has problems (for example, outside of cell phone/WiFi coverage areas). They even have a web page of iPhone app resources.

[l008com]

So how accurate is the iPhone's GPS, does anyone know? I'm not talking about when augmented with wifi&cell, just the straight GPS. I will be in the woods to cell triangulation won't help me a whole lot.

[ghporter]

It depends on the app you're using. MotionX needs cell contact to acquire satellites-I'm not sure about other apps. But once acquired, MotionX should continue tracking the satellites and providing generally ±20' at best accuracy. Definitely good for mapping hikes and other similar tracks.

[l008com]

My plan is to record multiple 'runs' of each trail, then lay them all on a canvas and draw a map out of them with illustrator.

[cgc]

Originally Posted by l008com 

... Within a few feet would be plenty for the map I'd like to draw. IF it's +/- 50 feet, that probably won't work...

GPS won't get you that kind of accuracy...

[Cold Warrior]

What model iPhone are you going to use? I've read some reports that iPhone 4 gets much better precision. If you aren't in moderate to thick tree cover, I bet you'll get better than 50 feet if you give iPhone time to lock onto the gps satellites (it may take 12-13 minutes to acquire and receive ephemeris and general atmospheric corrections from the satellites).

GPS precision depends upon your iphone's ability to get a good signal from many satellites. This can be diluted by low-atmosphere disturbances (e.g., in the troposphere), radio signal multipath, and fewer satellites visible to the phone (receiver). Accuracy also depends upon the geometric relationship of satellites in orbit to each other.

You alluded to this, but iPhone also uses A-GPS, which is a protocol where the cellular network provides some more or updated information (timing, ephemeris, etc.) and can even do a lot of the calculations for the phone, all of which can result in a good degree of precision.

[l008com]

It will be a new iphone 4 cdma. I will be in the woods but the woods are surrounded by city so it shouldn't be too bad. My plan would be to put the phone in my pack when i leave my house, with the GPS app fired up and recording (in the background), go for my bike ride, then when I get home, download all the data. There are also plenty of USGS markers in the woods I could mark as waypoints. I suspect that if i law over several runs of the same trail, over the winter satellite image i have (no snow but no leaves either), I should be able to draw a very accurate map.

[cgc]

I think the iPhone GPS would be fine for use as a bicycling GPS so long as your rides aren't too long (not sure battery life of iPhone CDMA but it'll probably be slightly less than a GSM iPhone).

GPS should be accurate enough to track a bike ride.

[ghporter]

Originally Posted by cgc 

GPS won't get you that kind of accuracy...

MotionX reports much better than ±50' accuracy in situations when stand-alone GPS devices also report such high accuracy. I've put a Garmin eTrex side by side with my 3Gs running MotionX and seen the phone report ~±20' accuracy when the eTrex reports about the same. Since I've seen the eTrex give me repeatable accuracy of less than 10' at times, given clear skies at the horizon, I trust its reports. Using this as a comparison, I believe that MotionX reports expected accuracy correctly in similar situations.

[cgc]

Originally Posted by ghporter 

MotionX reports much better than ±50' accuracy... I've...seen the phone report ~±20' accuracy when the eTrex reports about the same.

[QUOTE=l008com;4046330]...Within a few feet would be plenty for the map I'd like to draw.QUOTE]

I was initially replying to the OP that GPS won't give you accuracy to "within a few feet" but later said that it should be fine as a bicycle GPS.

[Person Man]

Originally Posted by l008com 

My plan would be to put the phone in my pack when i leave my house, with the GPS app fired up and recording (in the background)

The phone needs to be out in the open. If you can find some way to mount it on your bike that would be perfect.

[Demonhood]

I use Runkeeper for running and bike rides. Start it up, click the lock button, and then stash it in a backpack if you're on a bike. Everything syncs with their website and you can export the data afterwards (just checked - GPX & Google Earth).

[ghporter]

Originally Posted by cgc 

Originally Posted by l008com 

...Within a few feet would be plenty for the map I'd like to draw.

I was initially replying to the OP that GPS won't give you accuracy to "within a few feet" but later said that it should be fine as a bicycle GPS.

Yep. But our posts passed by each other as they were submitted, so my reply to your statement from the 26th was being composed as you were posting that it would be a fine bicycle GPS. And I wanted the chance to geek out on how cool it's been to have my phone and GPS agree so closely, so I posted a lot more than something saying "what do you define to be 'a few feet?'"