Is the iPhone GPS accurate?

“I am looking at purchasing your Deed Calls – Grid – Stakeout app for my iPhone to help me find my property boundary stakes from an old survey. Does it use the GPS off the iPhone? Is that typically accurate enough to get started? Or do you recommend some other GPS devise to use. If so, any suggestions that are reasonable priced?”

The app can use the GPS off the iPhone. It is not quite accurate, probably around 10 meters. Many users purchase the Dual XGPS 150-A or the Bad Elf GPS to get 2 – 5 m accuracy. These are relatively inexpensive. So, if you think you will be able to find a stake within an area of 30 ft x 30 ft, then use your iPhone GPS. If you only want to search within an area of 15 ft x 15 ft, then get the Dual or Bad Elf receiver. You could try it first using just the iPhone and see how it goes.


How to improve position accuracy of recorded points

When using a consumer-grade GPS, you may find that the device does not pin-point your exact location. Sometimes the GPS marker can be quite a distance away from your actual position.

As we’ve mentioned in a previous post, there are many factors that affect the accuracy of the computed GPS position. Some of those factors are out of your control. GPS differential correction can help remove some sources of position errors, but consumer-grade GPS does not provide differentially corrected GPS data.

Nevertheless, you can do a few things to help improve the position accuracy of the points logged. First of all, make sure your device has a  good view of the sky and is not obstructed by nearby objects (especially reflective ones) or buildings. Secondly, after turning on the GPS device, wait 8 – 10 minutes until it settles down. This will be indicated by the GPS marker  settling close to where it should be (if you are doing this at a reference location) and is not jumping all around. Then you would start recording your point positions. If you are using iCMTGIS II or iGPS GIS II, you can usually get a reasonably good position by setting the Time Session to 300 seconds (5 minutes).

Remember that each time you turn GPS off from your app and turn it back on, you will need to wait a few minutes for the GPS to settle down. Same if you turn off an external GPS device then turn it on using its ON button.

GPS accuracy on an iPhone, iPad or iPad Mini

We have received many inquiries about the GPS accuracy on various models of the iOS devices. This is a question for Apple to answer, but the coveted information is nowhere to be found in the product specs.

In general, consumer-grade devices that are sold separately, or the GPS built into some PDAs, the iPhone or the iPad, are not of high accuracy, but can be used to satisfaction for determining larger acreages.  Point position accuracy generally improves if you log a number of GPS fixes at one location then have the average value computed. Such functionality is provided by iCMTGIS II and iGPSGIS II.

The accuracy provided by consumer-grade GPS can range from 1 m to 20 m, depending on the device and the conditions under which the measurements are made. The iPad Mini with cellular and the newer iPhone models provide GLONASS capability. These will offer better GPS position accuracy than the older models.

A number of consumer-grade GPS devices claim 1-3 m or 3-5 m, accuracies. Some of them are compatible with the iPhone and iPad (e.g. Dual XGPS150A, Garmin GLO GPS + GLONASS, Bad Elf GPS PRO) . We heard that there will soon be external Blue-tooth GPS devices with sub-meter accuracy available for use with the iPad. However, keep in mind that better accuracy usually comes with a higher price tag.