How to use Pix4Dcatch with viDoc RTK rover


Using PIX4Dcatch with a viDoc RTK rover enables RTK-grade 3D scanning with the iPhone or iPad.

Basic requirements:
  • PIX4Dcatch iOS app on an iPhone or iPad.
  • viDoc RTK rover.
  • NTRIP service subscription. 
  • Internet access.
  • PIX4Dmapper, PIX4Dmatic or PIX4Dcloud license for processing.

Install PIX4Dcatch

At the moment, PIX4Dcatch with the viDoc RTK rover is only available on iOS. To set up PIX4Dcatch:

  • Install PIX4Dcatch from the App store.
  • Start PIX4Dcatch.
  • Select the Pix4Dcatch account icon icon on the screen.
  • In the Account Details, select:
    • (New users) Create account and create a new PIX4D account.
    • (Existing users) Log in with an existing PIX4D account.

Once PIX4Dcatch is installed on the device, you can already start acquiring datasets using the integrated GNSS sensor. 

To get precise image geolocation, check the next chapter Connect PIX4Dcatch to the viDoc RTK rover.

Connect PIX4Dcatch to the viDoc RTK rover

Before starting the image acquisition, charge the viDoc RTK rover for 6 hours.

Note: To mount viDoc RTK rover on the device.
The iPad:
  • Loosen the screw at the bottom of the rover.
  • Mount the rover onto the iPad, positioning it at the center.
  • The iPad has inbuilt magnets in its outer edges that ensure that the device is centered.
  • Once positioned, tighten the screw to the point at which the rover.
The iPhone:
  • Insert the iPhone into the SP connect case.
  • Mount the rover to the case by following the instructions provided with the SP connect case.
  1. Mount the viDoc RTK rover to the mobile device
  2. Turn on the rover with a single long press. The green light on the rover indicates it is turned on.
  3. Open the device settings and turn on Bluetooth.
  4. Start PIX4Dcatch.
  5. In the top-left corner of the screen, select the signal indicator and select viDoc RTK via Bluetooth.


    Select viDoc RTK via Bluetooth.

  6. In the RTK Device Settings dialog:


    Select the viDoc RTK rover, the NTRIP details, mountpoint and input coordinate system.

    • Select the viDoc RTK rover under Available Bluetooth Devices.
    • Enter the NTRIP details and select Connect:
      • Hostname / IP
      • Port number
      • Username
      • Password
    • When the connection is established, select Choose mountpoint and select the preferred mountpoint.
    • Select the input coordinate system.
Note: The input coordinate system is determined by the NTRIP service provider and is usually in the system that's local to the country. For example, we have identified that for most European countries, it is ETRS 89 (EPSG 4258) and across the US it is NAD83 (EPSG 4269).

7. Select Save.

A successful connection to the NTRIP service is indicated with a green Pix4Dcatch_viDoc_RTK_fix.png RTK icon.

Note: Turn off the viDoc RTK rover after every use to avoid additional charges from the NTRIP service provider.
Important: Please ensure that the device clock is synchronized. In order to synchronize the clock in the iPhone or iPad:
  • Open the Settings app.
  • Tap General.
  • Tap Date & Time.
  • Verify that Set Automatically is toggled to the right and appears green.

Capture a dataset

Once the viDoc RTK rover is successfully connected to PIX4Dcatch, wait for the RTK fix. For an optimal experience, make sure the antenna is not obstructed and that you have a good internet connection.

For more information on acquiring images, see PIX4Dcatch - (Android, iOS) Getting started article.

Example: After the RTK fix is established, the Horizontal Accuracy and Vertical Accuracy are in the range of a few centimeters. In ideal conditions, the values are close to 0.01m.


Make sure Accuracy is close to 0.01m, Status is RTK Fixed and HDOP is ideally below 1.

Check the Status and the HDOP during the acquisition to ensure that the conditions are optimal.


Status Explanation
No fix The data is not valid, not enough satellites visible or internet connection problem.
Autonomous GNSS fix Only Differential GNSS is used for data measurements. DGNSS is an enhancement to GNSS which determines its location bases on reference station, no fixing of ambiguities. The accuracy of the determined position can be in the range of 10 m or more.
DGNSS Only The data is not valid, not enough satellites visible or internet connection problem.
RTK Float The device does not have enough satellites in common with the base station (i.e., Mount Point) or reflected signals of satellites are received. The accuracy of the determined position can be in the range of 1 m.
RTK Fixed The GNSS rover and base station (i.e., Mount Point) can see at least five satellites in common, and the rover is receiving corrections from the base station. The accuracy of the determined position can be in the range of a few centimeters.

HDOP (Horizontal Dilution of Precision) gives an indication of how good the position and distribution of the satellites is. More in the Dilution of precision (navigation) article.

Generally, the HDOP value is considered ideal below 1, and to have centimeter level accuracy, from some testing, it has been observed that for a better accuracy we should take the readings which have a value lower than 0.65.

The accuracy values can vary and depend on multiple factors, for example:

  • Blocked and reflected GNSS signal, close to buildings, trees, or bridges.
  • Rapid movements of the device.
  • Poor cellular reception.

For more information, see GNSS and viDoc RTK rover best practices.

Process the dataset

After the image acquisition is finished, it is possible to Upload and process on PIX4Dcloud or Process locally with PIX4Dmapper.

When uploading on PIX4Dcloud, it is possible to change the output coordinate system:

  • Click the PIX4Dcatch_coordinate_system.png coordinate system tab.
  • Select the horizontal and vertical coordinate system in which you would like the outputs to be.
  • Click Upload.


Uploading to PIX4Dcloud after selecting the output coordinate system.


Searching for the desired output coordinate system before uploading to PIX4Dcloud.

Note: When uploading a project with the RTK image geolocation it is possible to select the Output coordinate system. The Default is the autodetected UTM zone corresponding to the location of the project.
Important: The dataset can be processed with a valid license:
  • A PIX4Dcloud (PIX4Dcloud and PIX4Dcloud Advanced) license is required to upload the project for cloud processing.
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