Fulcrum can use a connected external GPS receiver instead of your device's built-in GPS chip. External receivers, especially RTK (Real-Time Kinematic) models, can improve location accuracy from several meters down to sub-inch levels, which matters for surveying, utility locating, asset inspection, and other precision fieldwork.

This capability works the same way on the Android and iOS Fulcrum apps except where noted below.

Fulcrum has been tested with the following external GPS receiver brands. This list will grow as we test more devices. See the note below the table if your receiver isn't listed.

All supported devices connect to your phone or tablet over Bluetooth.

There are two ways to open Location Sources:

Once you're on the Location Sources screen:

If your receiver doesn't appear in the list, confirm it's powered on, charged, paired over Bluetooth at the OS level (see above), and close enough to your device.

Trimble devices are set up through Trimble's own app, Trimble Mobile Manager (TMM), rather than directly in Fulcrum.

For non-Trimble receivers, Fulcrum needs to know the height of your GPS antenna above the ground so it can correct your recorded position accordingly.

Your antenna height settings persist across sessions, so you only need to set it once per device. The unit shown (feet or meters) is based on your device's regional measurement system settings, the same setting that controls units elsewhere in the Location Editor.

Once a location source is active, a status banner appears at the top of the Map View and the Location Editor. It moves through five states over the course of a session:

As with antenna height, the accuracy value shown here follows your device's regional measurement system settings (feet or meters).

The values shown for an external receiver come from the NMEA sentences your receiver sends over Bluetooth. Fulcrum displays every value it receives; it doesn't filter or standardize this data, so the exact fields available in GPS Details can vary by manufacturer and model, depending on what that receiver's NMEA output includes.

In the Map View or the Location Editor, the Navigation button cycles through three modes each time you tap it:

Panning, zooming, or rotating the map with your fingers always drops you back to Manual. If your external receiver disconnects mid-session, the Navigation button keeps working using Device GPS.

To make sure the point you capture matches the exact coordinates coming from your external GPS receiver, use Follow mode. It's the only mode that keeps your position locked to your receiver's live location. When an external GPS receiver is your active source, Fulcrum automatically opens the Map View and Location Editor in Follow mode, so you don't need to switch to it manually.

While an external GPS receiver is your active source, Fulcrum forces the map into Target Mode. The toggle to switch to Tap Mode is disabled, with a short explanation shown beneath it. Tap Mode becomes available again as soon as the receiver disconnects or you switch back to Device GPS.

When you place a point in Target Mode with an external GPS receiver active, Fulcrum stores the full raw GPS data (the complete NMEA sentence output from the receiver) along with that point, in addition to the standard GPS metadata — latitude, longitude, altitude, and horizontal and vertical accuracy — that Fulcrum already records for every point. If you place a point manually in Tap Mode instead, this GPS metadata isn't saved with the record, even though an external receiver is connected. For lines or polygons, including tracks, Fulcrum captures this GPS metadata for the track's last vertex only, not for every vertex along the way.

On the web, this data shows up in a new GPS Data section in the record editor, alongside the location metadata Fulcrum already shows for a record. This section only appears on records that were captured using an external GPS receiver — you won't see it on records collected with a device's built-in GPS.

This raw GPS data is stored under the field name gps_device_capture. That column isn't shown by default in the web Data Viewer, but you can enable it from the column picker there, and it's also included in data exports — the column holds the receiver's raw GPS payload for the record.