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Horizontal grid corrections and transformations

Hi all,

If a horizontal coordinate system transformation is required to accurately transform your project’s Image Geolocation Coordinate System or GCP Coordinate System to your project’s Output Coordinate System, you must transform your project’s inputs’ coordinate system to your project’s Output Coordinate System before processing your project.

You can use compatible third-party software to transform your project’s inputs’ coordinate system.

If you are unfamiliar with horizontal coordinate system transformations or are unsure if your project requires a coordinate system transformation before you start processing, consult with the party that collected your project’s images or ground control points for more information.

Examples:

The following are two examples of a pair of coordinate systems that require a more accurate coordinate system transformation than Pix4D’s image processing engine supports at this time.

Ground Control Point Coordinate System and Output Coordinate System do not match (CH1903/LV03 and CH1903+/LV95):

You measured your project’s ground control points in CH1903/LV03, but you want to define your project’s data products in CH1903+/LV95. To ensure that you acquire the most accurate results possible, you must transform your CH1903/LV03 ground control point coordinates to CH1903+/LV95 before you process your Pix4D project.

Switzerland’s Federal Office of Topography offers a tool for accurately transforming between CH1903/LV03 and CH1903+/LV95.

  • Use REFRAME to transform your ground control point coordinates from CH1903/LV03 to CH1903+/LV95.
  • Import your transformed ground control point coordinates via the GCP/MTP Manager and set the project’s GCP Coordinate System is set to CH1903+ / LV95.
  • Set your project’s Output Coordinate System to CH1903+ / LV95.
  • Start processing.

Image Geolocation Coordinate System and Output Coordinate Coordinate do not match (WGS 84 and OSGB 36):

Your project includes WGS84 cm-grade geotags but you want to define your project’s data products in OSGB36, and your project does not include any ground control points. To ensure that you acquire the most accurate results possible, you must transform your WGS84 image geotag coordinates to OSGB36 before you process your Pix4D project.

Great Britain’s Ordnance Survey offers a tool for accurately transforming coordinates to OSGB36.

Thank you!

Pix4D Support Team

3 Likes

Why, then, do you offer the option to select different coordinate systems for images, GCPs, and output, if you say here that all must be the same?

Hey Etienne,

This article is offering a solution to achieve a high accuracy of a few centimeters, which is possible especially when using RTK datasets. Pix4D is using a 7-parameter transformation formula, which can only yield an accuracy of a few meters. Meter-accuracy is acceptable for the most datasets with standard image geotags such as images captured with consumer drones. On the other hand, external tools such as the ones offered by national mapping institutes use specific parameters for transforming datasets and can yield a cm-accuracy. 

Cheers,

Teodora

1 Like

one more doubt 

i have opened .tiff in global mapper

what should i select when this pop ups ?

i want to be sure i m making the right choice

 

https://prnt.sc/on04zm

Hello Curt,

If it is fine for you, let’s proceed with this topic on the ticket you opened on Zendesk. A technical support dedicated for coordinate systems will take care of your request.

Best,

Teodora