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Author Topic: Changing Coordinate System  (Read 445 times)

SvSz

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Changing Coordinate System
« on: February 11, 2024, 01:24:39 AM »
Hello Folks,

My project covers roughly 1 kmĀ² so I needed to think about the right coordinate system.

We took around 4000 photos with a DJI Matrice. Exiftools says the images use GPS Map Datum: WGS-84
Am I even able to transform these images from the global WGS 84 to a UTM ?


I created a dense point cloud in WGS 84 / EPSG::4326. When exporting the Dense Cloud I can again change the CS. I chose EPSG::32632 because that fits my area more accurate.

I compared this export to another one: I created the Dense Cloud in 4326 and then changed the reference system to 32632. Dimensions of the surveyed area shrunk by a factor of 5 or so. Again I exported the DC also in 32632.

I compared both DCs in CloudCompare. They appear shifted and in different dimensions. The second one is smaller (kind of as expected).

This is more about Cloudcompare now, but it confuses me further:
When analyzing the face of the surface with the Compass Plugin in CC both Exports where not accurate in their Slope Direction (a value of how much is slope face deviating from North) and Slope Angle.
Especially when the first Export has almost the expected value (I know the value from a map) I really started to wonder what's going on.

Can someone explain what I need to do or what I did wrong because this is confusing. I am currently starting the project all anew and begin the Project in 32632 and THEN create the Dense Cloud in it and THEN export it, also in 32632, so it's generated and exported in the same system... That's the last thing that could be wrong but I guess it's not.

Hope you can help...

Edit: I guess I need to transform the image exif data to 32632 or work with 4326. I prefer Option 1, but until now I did not find a tool to do this, only python script and this can become pretty unhandy when working with several thousand of images, I guess.

Edit2: Screenshot.
The exif data says it has the GPS Map Datum "WGS-84". Is that even equivalent to 4326 and why does an image need this information? As long as there is only one coordinate attached to the image, there is no need for a projection, am I wrong?  ???

Cheers.
SvSz
« Last Edit: February 11, 2024, 04:37:03 PM by SvSz »

SvSz

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Re: Changing Coordinate System
« Reply #1 on: February 11, 2024, 04:50:09 PM »
Here is a comparison of the Survey Statistics.

I went to the Chunks' Reference Settings and changed the Coordinate System.

Chunk1 with EPSG 4326 is completely fine.
Chunk2 with EPSG 32632 makes no sense at all.

Why is that? Yes, the pictures have the GPS Datum WGS 84 in it, but is that so important? The image is only a single coordinate point, there is no need for a projection, and in my understanding, there should not be a problem, but apperently is...
« Last Edit: February 11, 2024, 05:02:27 PM by SvSz »