viDoc RTK rover for Pix4Dcatch - FAQ

What is the viDoc RTK rover?

The viDoc RTK rover is a device that can be mounted onto Apple iPad Pro, iPhone 12 Pro and iPhone 12 Pro Max products. The rover, synchronized with Pix4Dcatch, geotags images with RTK accuracy in real-time, while connected to any NTRIP service, allowing absolute accuracy in 3D photogrammetric scanning.

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

Conceived by viGram GmbH., a German company led by professional surveyors, the viDoc RTK rover is designed with an eye for accuracy and works with Pix4Dcatch for image acquisition. The hand-held RTK rover is a replacement for more expensive ground surveying equipment that does not compromise on accuracy to achieve 3D, actionable results.

For more information see viDoc RTK rover product page. 

How to use the Pix4Dcatch with viDoc RTK rover?

Basic requirements:

  • Pix4Dcatch iOS app on the iPhone or iPad.
  • viDoc RTK rover.
  • NTRIP service subscription.
  • Internet access.
  • Pix4Dmapper or Pix4Dcloud (Advanced) license for processing.

Once the latest iOS version of Pix4Dcatch is installed, select the viDoc RTK via Bluetooth settings. More information in the How to use Pix4Dcatch with viDoc RTK rover article.

What are the recommended devices?

How are the images captured in Pix4Dcatch synchronized with the viDoc RTK rover?

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. In case 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+viDoc RTK rover?

The orientation of the geotagged images are indirectly computed from the internal IMU (Inertial Measurement Unit) of the mobile device and not from the viDoc RTK rover.

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

Yes, the offset is automatically taken into account.

Can I generate a 3D model or 2D map in a coordinate reference system of my choice using Pix4Dcatch+viDoc?

Yes, you can select the coordinate system in Pix4Dmapper and get the 3D model or 2D map in a coordinate reference system of your choice or transform the image geolocation in the desired coordinate system with a third-party software.

More in the Select Output Coordinate System in Pix4Dmapper article.

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

The heights are always based on the ellipsoid (GRS80) and they cannot be changed directly in Pix4Dcatch.

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

  • Use a third-party software and transform the heights from ellipsoid to geoid before importing them into Pix4Dmapper.
  • Use the Geoid offset above 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 viDoc RTK rover 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+viDoc should be precisely synchronized to within 100ms.

Please ensure that the device clock is synchronized. In order 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 viDoc RTK rover for Pix4Dcatch be used without an internet connection?

No, you need an internet connection 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 to upload the data to Pix4Dcloud for generating the 3D model.

Can I do PPK or use my own base station?

The viDoc RTK rover 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 + viDoc RTK rover over time?

Yes, Pix4Dcatch with viDoc RTK rover 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 + viDoc 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 in the How to merge projects article.

How can I purchase the viDoc RTK Rover

Contact us directly for the purchase of the viDoc RTK rover.

How can I get technical support for viDoc RTK rover?

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

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

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