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Coordinate conversion and negative altitude values

Hi everyone, just wondering if someone could help.

I carried out my first flight yesterday over a earth works site and my intention is to create a 3d point cloud of the site for volumes etc. I took around 460 photos with the dji phantom 4 pro, and I have ran it through pix4d desktop. Firstly I noticed all the altitude values were negative. To solve this I just exported a CSV to excel made the values positive, and brought it back in. Is this appropriate or will this mess with the accuracy of the data processing?

Secondly, I wanted to select a different coordinate system from googles WGS 84 system which is giving me lat and long to NZGD Mt Eden 2000 which will give me X,Y. However when I do this none of the coordinates on the photos translate over to the selected system and when I run the initial processing (step 1) it totally fails. Does the software not have these projections and translations built into it? Any advice on these steps would be hugely helpful
Cheers jess

When you go to process the 1 step you can choose the output coordinates. The WGS 84 are the standard coordinates for the images in DJI. The Z value its normal to have big differences between gps coordinates and local coordinates. No problem to change Z manual but I recommend having GCP’s with the correct coordinates to really have a good 3d positioning and scale of the project 

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I agree with Jorge on the first reply. The coordinate system of the images is WGS84, because that is how DJI stores the coordinates. If you want to change the coordinate system of the project, you would have to change the output coordinate system (Project > Select Output Coordinate System). 

As for the coordinate system NZGD Mt Eden 2000 you can select it with the EPSG number: 


The website spatialreference.org has a good database of existing coordinate systems, e.g. http://spatialreference.org/ref/epsg/nzgd2000-mount-eden-2000/ 

More on how to modify coordinate systems (image, GCP and/or output) coordinates in this article: https://support.pix4d.com/hc/en-us/articles/202560029

Thanks guys. Managed to bring it in and attach it to some GCPs.
Cheers

Great! Glad that it worked out :slight_smile:

Cheers