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Wrong Orthometric Heights

All of my images are in Lat Lon WGS 84. My coordinate system is NAD83(2011) / Texas South Central (ftUS) - EPSG:6588. I have set my vertical system to NAVD88 height (ftUS) - EPSG:6360 and the Geoid to Geoid18. After I process, I am still getting ellipsoid height. Since the survey was set up based on an OPUS survey, I know this is correct. Not sure of how Matic works, but in our survey equipment, if we set up a horizontal coordinate system with a geoid applied, orthometric heights are returned when measurements are taken. In Mapper, I would apply the geoid offset and orthometric height where returned.

When I select a point in the cloud I am getting an ellipsoidal height, not an orthometric elevation.


The value indicated by the arrow above should be 21.79 feet if the geoid was being applied.

Hi @Vertical_Aspect_Supp, thanks for contacting us and for sharing the screenshots.

I could not find any obvious reasons why you are getting the ellipsoidal height even after you specify that you project should be in orthometric heights.

You mentioned that your images in are in WGS 84 (EPSG:4326), but what about the vertical coordinate system? Are the images based on the ellipsoid or the geoid?

Would it be possible to share 3 images from the project and the quality report?

Best,

Hello Blaz,

The images came from a DJI M300 with the P1 Camera. The data processed correctly in Pix other than some known problems with the camera orientation. I also tried the project in MSL with a geoid offset and still get a wrong answer on the elevation. I have sent a complete set of images to Ryan Sweeney (US Pix4D Rep) and here is a link to some images: https://we.tl/t-I7MOwgjFph

Hi,

do you know if the height of your images is measured with respect to the ellipsoid or MSL, for example, EGM96?

Do you by any chance have a text file with image coordinates? Or the image geolocation is only available directly in the EXIF of images?

Best,

Hello Blaz,
The images are ellipsoidal height and come directly from the EXIF data from the P1 camera. The images will process correctly in Pix4DMapper, except for the problem of a camera model in Mapper. The issue is not the data. The issue the problem of the geoid offset or geoid model not being applied properly. I have processed another project in Matic with the same problem being evident.

Thank you for additional information.

I had a look and the vertical coordinate system is set to EGM96 when importing the DJI Zemnuse P1 images into Pix4Dmatic, and not ellipsoidal height.

In other words, Pix4Dmatic treats images as if they are in EGM96 and then transform them into Geoid18 that you selected in coordinate system dialog. Do you think this could explain the offset that you get?

I will talk about this with the product team in order to change the automatically detected vertical coordinate system for DJI Zemnuse P1 to ellipsoidal heights.

Best,

I have to take your word for this since I have no control over the camera coordinate system as in Mapper. Matic is much more of a “Black Box Solution” than Mapper, and I am not sure that I like that as a Land Surveyor.

Since this is the behavior for other DJI drones in the past, this could definitely be the problem. I did check the elevation of one of the cameras in Matic vs. the same in Mapper and there was a 4.62-foot difference. I then computed the EGM96 and the Geoid 18 values and subtracted and came up with a distance of 4.61 feet. This would indicate that the EGM 96 value is being erroneously applied. I have never understood why you would apply a geoid value to the image. This was the first thing I advised clients to change in Mapper.

Hi @Vertical_Aspect_Supp,

We understand that and are working on exposing an option to select the coordinate system of the cameras, as well as viewing the external camera parameters (geolocation, orientation) and their accuracy. There should be more by this summer.

Note that it is already possible to import a .csv/.txt file for the image geolocations and orientations and to define the coordinate system that applies to these: Image geolocation and orientation import format – Support. Would you have a way of getting these values in a .csv or .txt file and import it? This could be a workaround until the coordinate system of the camera can be selected directly for data in the EXIF.

Thanks for the reply, but the only way I have to get that information is by exporting from Mapper. If I am going to load in Mapper, I might as well process in Mapper.
am going to create a camera calibration for use in mapper and will continue with this solution for the time being.