This will be my third and final installment in a series of articles discussing device I’ve used when preforming surveys when contributing to OSM.

In the first article, I talked about accuracy limitations associated with GPS signals while the second gave an overview of four specific mapping devices I’ve personally used. In this article I’ll compare the accuracy of three devices previously discussed using GPS traces.

Test Setup

To test device precision, I recorded GPS traces along a hike with a variety of line-of-sight obstructions to the sky with each device recording at the same time. The traces were assigned colors to help differentiate each device:

• Samsung Galaxy S10e - Orange
• EcoDroidGPS - Green
• Garmin GPSMAP 66sr - Purple

The arrangement of the devices are as follows:

• The EcoDroidGPS was placed in a backpack with the reciever on an antenna mast above my head.
• The Garmin was attached to one of the backpack straps with the built-in antenna stub poking just above my shoulder.
• The S10e was in one of the side pockets of the backpack.

The EcoDroidGPS and S10e location information were sampled every one second within a GPX track using the app OsmAnd. The 66sr records as an “activity” with location information sampled every one second. The resulting GPX track was downloaded from the device.

Results

The Bridge

Before arriving to the trailhead, I had to walk along the shoulder of a bridge spanning a medium size river. The bridge is long enough to offer a best case scenario for accuracy. There is a good 45 degrees of sky visible from most angles in the center of this bridge.

The result of a stretch of road with minimal interference is quite predictable, all three traces are stacked right on top of each other without significant deviation.

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In this article, I’ll continue sharing my experience on finding a generally-available commercial device to be used with preforming surveys for contribution to OSM. I previously wrote about GPS precision and why, by itself, it is limited to meter precision.

Below are the devices I’ll be discussing based on my own usage. I’ll share how I used them and my thoughts on each. In a final article of this series, I’ll provide a GPS trace comparison of the EcoDroidGPS, smartphone, and Garmin GPSMAP 66sr as well as which device I’d pick if doing it all over again.

• Modern smartphone (Samsung S10e)
• EcoDroidGPS
• Garmin GPSMAP 66SR
• DIY (simpleRTK2B or Arduino solutions)

Modern smartphone (Samsung S10e)

The first device I used for surveys and general contributions to OSM was with a smartphone. I currently use a Samsung S10e with the below Android apps depending on the complexity of my contribution:

• OsmAnd - Used for adding basic POIs and creating GPS tracks with built-in plugins.
• StreetComplete - Used for casual contributions and tag refinement on existing features.
• Vespucci - Used for more complex editing of most features in OSM. Offers an editing experience like iD or JOSM, except on mobile.

Not surprisingly, since I generally have my phone with me, this is the most convenient when I stumble across mapping opportunities in the wild. The location accuracy is acceptable. It can be used to map larger roads and general POIs without issue, but is not accurate enough to trace a sidewalk or trail. I’ve also noticed that accuracy improves in urban areas likely due to the ability for Google’s location services to supplement GPS data with nearby WiFi access points and Bluetooth.

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I’ve spent a fair amount of time looking for the “perfect” consumer device to be used in my on-the-ground surveys that provides better-than-average accuracy without spending thousands on survey-grade equipment. This article series is an attempt to catalogue my experience to those who are interested.

Before diving in, I’d like to review the obstacles to accuracy when surveying using GPS-enabled devices. While this subject may be common knowledge to those familiar, it took me a considerable amount of time to understand some of these points and was a major driving factor in my quest for the “perfect” device.

GPS vs. GNSS

Throughout this article I’ll use the term “GPS” to refer to the systems and satellites that provide longitude and latitude location information to a user. Please note that this is not 100% accurate, however, since “GPS” is a specific satellite (known as a “constellation”) location system among many. In fact, GPS is part of a general Global Navigation Satellite System or GNSS. Other GNSS systems are as follows:

• GPS
• GLONASS
• Galileo
• BeiDou

I’ll be using “GPS” in an attempt to minimize confusion to those (like myself) who were unfamiliar with this distinction until now.

Precision Limitations

In brief, GPS works by analyzing a time code that is continuously sent by satellites in orbit around Earth. Receivers take that time code from multiple satellites and determine how long it took for the receiver to receive the time code data. This information is then used to calculate a longitude and latitude location on Earth.

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