FAQ Pix4D supported RTK devices - PIX4Dcatch

What is a Pix4D-adapted RTK device?

Pix4D adapted RTK devices for use with Pix4D can be attached to certain phone devices or tablets. When paired with PIX4Dcatch, these devices can geotag images with RTK precision as they are captured. This synchronization allows for real-time connection to NTRIP services, ensuring absolute accuracy for 3D photogrammetry scans.

Extensive research has revealed that it is possible to achieve 3D models with an absolute geolocation accuracy of less than 5 cm. More information is in the white paper.

The hand-held RTK devices replaces more expensive ground surveying equipment that does not compromise on accuracy to achieve 3D, actionable results.

How to use the PIX4Dcatch with a Pix4D-adapted RTK device?

Basic requirements:

• PIX4Dcatch app.
• Pix4D supported RTK device.
• NTRIP service subscription.
• Internet access.
• PIX4Dmatic, PIX4Dmapper, or PIX4Dcloud (Advanced) license or trial for processing.

Once the latest version of PIX4Dcatch is installed, select the Pix4D supported RTK device via Bluetooth settings. 

What are the recommended devices?

How are the images captured in PIX4Dcatch synchronized with the Pix4D supported RTK devices?

The image acquisition in PIX4Dcatch is independently done from the recording of the GNSS data from the RTK rover. When the capture is complete and the project is saved, the geolocation information from the rover is tagged to the corresponding images based on the image timestamps. The orientation of the images is computed based on information from the AR tracking. If part of the GNSS data has low accuracy (for example, due to poor satellite visibility), relative AR positioning is used to improve the positions and accuracy.

How are the orientations of images set when using PIX4Dcatch+Pix4D supported RTK devices?

The orientation of the geotagged images is indirectly computed from the internal IMU (Inertial Measurement Unit) of the mobile device and not from the Pix4D supported RTK devices.

Is the offset between the rover's antenna and the camera taken into account?

Yes this is one of the most important things when you setup your RTK device, we currently offer measured offsets from known devices that can be selected from the app.

If your device combination with the RTK device isn't measured yet would be necessary to measure and enter the offset manually For more information check the respective article to your RTK device:

Emlid Reach RX

Trimble

Bad Elf Flex

viDoc distributed by Pix4D

Can I generate a 3D model or 2D map in a coordinate reference system of my choice using PIX4Dcatch+Pix4D-adapted devices?

It is possible to select the coordinate system when uploading to PIX4Dcloud/PIX4Dcloud Advanced, in PIX4Dmatic or PIX4Dmapper, to get the 3D model or 2D map in a coordinate reference system of your choice. You can also transform the image geolocation in the desired coordinate system with third-party software.

For more information:

• How to use coordinate reference systems in PIX4Dcatch.
• How to use coordinate systems in PIX4Dmatic.
• Select Output Coordinate System in the PIX4Dmapper article.

What is the height reference of the geolocated images and how can I change it?

The height is based on the ellipsoid of the input horizontal coordinate reference system.

In order to get the results georeferenced based on the local geoid, you can:

• Select the vertical coordinate reference system in PIX4Dmatic.
• Use third-party software and transform the heights from ellipsoid to geoid before importing them into PIX4Dmapper.
• Use the Geoid offset above the ellipsoid option in PIX4Dmapper.
• Use Ground Control Points to apply the shift.

Will tilting the device during data acquisition have an impact on the accuracy of the 3D models?

The antenna on the Pix4D supported RTK devices has the best visibility of satellites when it is directly pointing upwards (90 degrees). The more the antenna is tilted from the 90-degree position, the lower its accessibility to satellites. Hence, it is recommended to only slightly tilt the device from the ideal 90-degree position to a maximum of 20 degrees.

How precisely is the RTK trajectory synchronized with the images?

The images acquired from PIX4Dcatch+Pix4D supported devices should be precisely synchronized to within 100ms.

Please ensure that the device clock is synchronized. To synchronize the clock in your iPhone or iPad:

• Open the Settings app.
• Tap "General."
• Tap "Date & Time."
• Verify that "Set Automatically" is toggled to the right and appears green.

Can Pix4D-adapted viDoc RTK devices for PIX4Dcatch be used without an internet connection?

An internet connection is needed during data capture to stay connected to the NTRIP service.

An internet connection is also needed every time PIX4Dcatch is started for logging into the app and uploading the data to PIX4Dcloud for generating the 3D model.

Can I do PPK or use my own base station?

At the moment the Pix4D supported RTK devices only allows access to an NTRIP service to receive real-time correctional GNSS data. It is not possible to do PPK or to connect to your own base station.

Can I accurately acquire data with PIX4Dcatch + Pix4D supported RTK devices over time?

Yes, PIX4Dcatch with Pix4D supported RTK devices allows to capture and process a 4D model and visualize it on PIX4Dcloud Advanced's timeline. Due to the RTK accuracy, the 3D models at different times are registered with cm accuracy. You can use PIX4Dcloud Advanced sliders to compare orthomosaics or track volume changes of small stockpiles.

Can I combine RTK drone data and terrestrial PIX4Dcatch + Pix4D supported RTK devices mobile phone data?

Drone RTK flights, as well as PIX4Dcatch RTK data, can be combined in a single project inside PIX4Dmapper to obtain a 3D model that has the overview and roof data (from drone imagery) as well as the terrestrial details (from PIX4Dcatch mobile phone data).

More information about how to process such datasets is in the How to merge projects article.

How can I purchase the Pix4D supported RTK devices?

Contact us directly for the purchase of the Pix4D supported RTK devices.

How can I get technical support for the Pix4D supported RTK devices?

Pix4D customers: For technical questions, contact our support team.

Not a customer yet? Contact sales or post on the Pix4D Community.

Battery care and maintenance.

The following recommendations will ensure optimum performance and extend the life of your batteries:

• The battery is supplied partially charged. Fully charge the battery before using it for the first time.
• Try not to allow the batteries to fully discharge.
• Keep the battery charged continuously when not in use.
• If you need to store the rover, fully charge it before storage and then charge it at least every three months.
• To charge the battery, only use a charger/cable that is suitable for charging the lithium-ion battery.
• If the unit has been stored for more than three months, charge the battery before using the receiver.
• During operation, it is possible to charge the Pix4D supported RTK devices with a power bank when the battery status is low.

Which geoids are compatible with PIX4Dcatch and the RTK devices?