This document explains basic concepts of GNSS for more accurate survey location data and how to use a GNSS receiver with Survey123.
WHAT IS GNSS?
GNSS stands for Global Navigation Satellite System and is the more formal way to describe what many people call GPS. GNSS uses a group of satellites in space to provide location, navigation, and timing services anywhere in the world. All mobile phones and tablet devices have built-in GNSS capabilities, so that users can see their location using an app. Generally, the GNSS location data provided by a phone or tablet is within two meters of the actual location. To achieve a greater level of accuracy, additional technology is required.
Location information or data of higher accuracy can be obtained by using a GNSS receiver paired to an existing device such as mobile phone or tablet. The accuracy of a GNSS receiver depends on a user’s location, the type of device used, the configuration, weather patterns, and more. A user in one location may have varying accuracy measurements than a user in another location due to the availability, number, and position of satellites. Atmospheric conditions such as cloud cover and clear skies will affect the accuracy of a GNSS device.
GNSS RECEIVERS FOR SURVEY123
Survey123 can use GNSS capabilities that are built into mobile phones and tablet devices, or a user can add an external GNSS receiver to obtain higher accuracy data. There are many GNSS receivers available; however, not all of them work directly with Survey123. To use a GNSS receiver with Survey123, the receiver must support the output of National Marine Electronics Association (NMEA) messages.
To improve the accuracy of a user’s location, consider using a GNSS receiver that supports differential corrections. If the user is using an Apple device, they must also choose a GNSS receiver supported on the Apple operating system, iOS. While Cadasta does not have an exhaustive list of supported GNSS receivers for Android, Apple, or Windows devices, here is a list of commonly used GNSS receivers use:
Bad Elf GNSS Surveyor
Bad Elf GNSS Pro
Bad Elf GNSS Pro+
Eos Arrow Lite
Eos Arrow 100
Eos Arrow 200
Eos Arrow Gold
Garmin GLO 2
Geneq SxBlue II
Geneq SxBlue III
Juniper Systems Geode
Leica Zeno 20
It is important to review the specifications of the GNSS receiver that the project would like to use to ensure it is supported by the appropriate NMEA technology, otherwise it will not work with Survey123.
CONFIGURATION OF COMMON GNSS RECEIVERS
GNSS receiver devices can increase the location signal of a collection device, such as a phone or tablet, but simply pairing and connecting the GNSS device with a phone or tablet does not always lend to the most optimized accuracy and precision available. The Minimal Configuration option provides a general accuracy and precision increase, whereas the optimized configuration of the Survey123 form, seen in the next section, allows for advanced use of a paired and connected GNSS.
The previously mentioned, commonly used GNSS devices, including Garmin, Bad Elf, Trimble, and others, can be paired using Bluetooth and connected via the Survey123 application. Steps to pairing and connecting the GNSS receiver to a mobile phone or tablet are as follows:
- Open the mobile device and turn on the Bluetooth option;
- Select the Bluetooth icon and press it for several seconds until the options page shows up;
- Select the Add another device option and select the GNSS receiver;
- Open the Survey123 mobile app;
- Select the More Options icon;
- Select Settings;
- Select Location;
- Select Add Provider;
- The device will now try to find the GNSS receiver; and
- Once the GNSS receiver has connected, a notification will be shown to indicate that a connection has been made.
If the device is not appropriately configured, then the mobile phone or tablet and the GNSS receiver will not communicate appropriately leading to numerous technical failures and errors. If basic pairing is not sufficient then more advanced configuration of a GNSS receiver is required. Advanced pairing and configuration instructions are explained in the Optimized GNSS Configuration document.
COMMON PROBLEMS AND SOLUTIONS
The device is disconnected or the connection is not working.
Close down the Survey123 app and disable all bluetooth connections. You may also want to restart the mobile phone or tablet device. Then reestablish the bluetooth connection and open the app to pair the GNSS device in Survey123.
There is no satellite reception.
Move to an area with a clear sky and no tree cover, as cloudy and deep forest conditions may prevent the GNSS device from communicating with the satellites.
The location of the point is not in the correct place.
Try reestablishing the connection and moving to an area without trees or clouds.
- All links in this sections are from the European Space Agency and can be found at: https://gssc.esa.int
- GNSS Receivers General Introduction
- Generic Receiver Description
- Direct GNSS external receiver support in Survey123