Field Data Collection

The workflow covered in the Introduction included three phases: 1) Field Data Collection, 2) Desktop Analysis, and 3) Data Visualization. Here we'll discuss phase 1.We encourage the use of smart phones and tablets for data collection for these reasons:

• Most already have them!
• Many know how to use them
• They're intuitive
• They're portable
• Come with an on board GPS receiver (iPhone 5 uses GPS + GLONASS)
• Have on board cameras
• Can connect to wireless networks
• Access to the internet
• Email is available
• There's an app for that!

Equally as important they are accurate enough for most public health community mapping needs.  For a discussion on their accuracy read this post.There are a myriad of data collection apps available. Part of choosing one comes down to the operating system you are using. We'll cover the three best apps we found for iOS and Android. Our full report and individual user step by step user manuals for each can be found here.iOS (Apple iPhones and iPads)The two best data collection apps for Apples iOS are EpiCollect and GIS Pro. They both allow you to customize the data attributes you collect. One big difference is that EPI Collect is free and GIS Pro, at $299, is the most expensive piece of software we considered in our workflow. However, with that price tag comes a lot of great intuitive functionality.EpiCollect (available for both iOS and Android)To get started with EpiCollect you install the app on your device via Apple's App Store. You then visit the EpiCollect website  and set up a project. Simply give the project a name and design your data collection form. The form can be set up with a variety of attribute columns. For example, feature type, name, description and photo. For most users it takes a practice run to get used to the workflow to set up a data collection form. The second time it goes very smoothly. The project can then be uploaded, via your email address, to your iOS EpiCollect app. Examples of the data collection screen are shown below. On the left is the home screen, on the right is the data collection screen. After data collection, you can sync the mobile app with the website. The data can then be viewed both on the mobile app or on the website. The website also allows for the spatial data to be exported as either an XML or CSV file. Data collected by EpiCollect is limited to point locations. The data can then be brought into a desktop GIS such as QGIS. This will be covered in a future blog post.GIS ProGIS Pro is essentially a lightweight GIS application for iOS. Once purchased a user can have the app on both an iPhone and an iPad. However, each unique user needs their own license. As with EpiCollect, the user can set up custom data collection fields. One additional feature here is that users can collect point, line or polygon (area) data sets within the same project. The data can also be exported in a shapefile format which is then ready to be used by any desktop GIS package. GISPro also allows for sharing of GIS layers. With this feature a team of data collectors can all be working off of the same GIS layer. This is a valuable feature. With the high cost does come great functionality compared to EpiCollect. This was determined to be part of the best workflow and is reviewed more thoroughly in the final report.AndroidIn addition to EpiCollect, the other great app for Android devices is OpenData Kit, known as ODK Collect. The app is free. It is even more intuitive and makes project management even easier than EpiCollect.To get started you will use a companion website called FormHub. Simply sign up for a free account and design your form. Here your data collection form is designed in MS Excel, and a template Excel file makes generating your first form easy. Once designed upload your form and sync your device to your account and you are ready to collect data. On the device the data collection form presents itself as a series of pages for each question.When you are back in range of a network simply sync the app with your account. The data will then be available for download from the website in several formats.SummaryThese are the best apps we found out of dozens reviewed. All three were successfully tested in 2013 by our partners were found to work well. For additional reading download the full report . Step by step user manuals for each can be found here.

How Accurate is the GPS on my Smart Phone? (Part 2)

In Part 1, I introduced the three parts of the hybrid locational system used by tablets and smart phones. Now I'll discuss each individually.Assisted-GPS (A-GPS)A-GPS is by far the most accurate of the three systems on your phone. A-GPS operates a little differently than the typical handheld GPS receiver. The assistance is provided by the cellular network. When connected to a cellular network the smart phone will download data about the GPS satellite constellation. This allows the phone to lock in on a position much more quickly than it could otherwise. The GPS functionality of a smart phone can still be used if the cellular network is unavailable.  However,  when disconnected from a network your phone will take several minutes to hone in on your location, versus just seconds when the network is available.The A-GPS receivers on iPhones have steadily improved from the iPhone 3 to the iPhone 5. In addition to the U.S. DOD GPS system, the Russians have a satellite navigation system called GLONASS. The newest smart phones (e.g., iPhone 4S and iPhone 5) now have GPS chips that use both satellite systems giving increased accuracy!  Europe, India and China are also developing satellite navigation systems and in the not too distant future GPS receivers may be able to use several systems simultaneously and become even more accurate.WiFi and Network PositioningFor any GPS to work the antennae needs a clear view of the sky. Users of smart phones will frequently be in "urban canyons" or indoors. This is where WiFi and cellular network positioning become necessary. Both of these methods are used by smart phones as indoor positioning systems. The phone will use a hybrid approach, using all three methods to locate you. These other two technologies aren't nearly as accurate as A-GPS, but can still locate you sufficiently to find the closest vanilla latte!Generally WiFi positioning is more accurate than cellular network positioning. It uses wireless access points and measures the  intensity of the received signal from one or more networks to find the position. Interestingly it doesn't require your device to be WiFi enabled to work.Cellular network positioning triangulates your position based off of nearby cell phone towers. Phone companies have precise locations for their cell towers, which when combined with signal strength can be used to approximate your location. Both of these techniques are dependent on overlapping signals from either access points and cellular towers. Therefore they're more accurate in urban settings.So What's It All Mean?From numerous tests the typical GPS receiver will achieve an accuracy of 1-5 meters.  Unfortunately assisted-GPS accuracies have not been studied nearly as thoroughly as typical GPS receivers. The best studies to date are those by Dr. Paul Zandbergen at the University of New Mexico. In 2009 he published findings showing that an iPhone 3 had an average accuracy of 8 meters. In that study the error never exceeded 30 meters. Below are the results of his 2009 study including all three locational systems.

• 3G iPhone w/ A-GPS ~ 8 meters
• 3G iPhone w/ wifi ~ 74 meters
• 3G iPhone w/ Cellular positioning ~ 600 meters

Numerous anecdotal studies indicate that the iPhone 4S/5 has become more accurate. In 2011 Dr. Zandbergen tested several Android smart phones. Here he found the accuracies to be slightly better than the 2009 study. They ranged from 5-8 meters. It is likely that the iPhone 4S/5 is within this range as well. It can also be assumed that iPads and other Android tablets will be comparable.Other Options for Increasing AccuracyThere are several third party external GPS receivers that connect to the smart phone via Bluetooth. For example, the Dual 150S can be used to increase accuracy in more remote locations.  It can be worn like a wrist watch, placed on a car dash or strapped to a backpack. It will provide 2.5 meter accuracy and only costs $100.SummaryIf getting within 5-8 meters meets your data requirements smart phones and tablets are a great way to go. If you need greater accuracy you can combine an external Bluetooth GPS receiver with your device and get that accuracy down to the 2-3 meter range. If you require more accuracy than that you will need to invest in a mapping grade GPS receiver.

How Accurate is the GPS on my Smartphone? (Part 1)

Historically field data collection was a daunting task reserved for geographic information specialists (GIS) professionals, and the technical savvy crowd. This was largely due to the learning curve involved in operating mapping grade Global Positioning System (GPS) receivers. However, smart phones and tablets have changed that. They offer an amazing array of functionality in a portable, intuitive and ever more familiar interface. Think about all the technology packaged into one of these little devices:

• GPS
• Camera
• Network connection (3G, 4G, WiFi…)
• Email
• Internet
• Apps

They're actually better than the Tricorders we used to see on StarTrek!  They have a slimmer profile, probably weigh a lot less, have touch screens, bigger displays and can be used with thousands of available apps.One big question when considering smart phones or tablets for field data collection is, "How accurate are they?" A related question that must be answered is, "What kind of accuracy will meet the needs of my project?" You need to answer both of these questions to determine whether or not this technology will work for you. Usually survey grade GPS accuracies (sub meter or sub centimeter) aren't necessary for public health mapping. Getting within 10 meters is more than adequate to map facility locations, patient addresses, potential sources of disease or wellness. How Does GPS Work?The Global Positioning System (GPS) is a U.S. Department of Defense (DOD) system. It utilizes a constellation of 24 satellites orbiting the earth at an altitude of 12,000 miles. GPS devices compute your position by determining the distance between the GPS receiver and a minimum of 4 GPS satellites. The satellites transmit radio signals to the GPS receivers, allowing the calculations to occur. Initially GPS was established as a military guidance system, and I doubt anyone foresaw the popular use it has today.The iPhone has been equipped with an onboard GPS since the iPhone 3, and Android phones became GPS enabled at about the same time. Typically people use GPS to find restaurants and street directions. However, there's no reason these same devices can't be used for public health data collection!More About Smart Phone Locational Services Smart phones in fact use more than GPS to locate you. They employ a hybrid locational system combining three separate technologies:

1. Assisted GPS (A-GPS)
2. WiFi positioning
3. Cellular network positioning.

These three technologies are used in combination as they are available. A-GPS is the most accurate of the three, and cellular positioning the least accurate. The figure below shows an example of the accuracy of each of these locational services.GPS AccuracyThere are a number of factors that affect accuracy no matter what GPS receiver is being used. The GPS radio signals encounter differing conditions while travelling through the atmosphere, causing signal delays, and therefore affecting accuracy. The geometry of the satellites being used will also vary. The GPS will have a wider array of satellites to choose from if you're out in the middle of a big field, versus being on 6th Avenue in Manhattan. You will get better positions if the satellites you're locked onto aren't clustered in one part of the sky. Therefore the more sky view you have, the more accurate your GPS will be. In addition to blocking your view of the sky, urban canyons can also cause multipath effects, where the GPS signal bounces off of buildings or other objects reducing accuracy.In part 2, I'll discuss each of the three pieces of the hybrid locational system individually, and discuss exactly what kind of accuracy you can expect to achieve.