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Topics - ChrisC

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I have an area where I created a DEM and orthomosaic but when I zoom way in on the pixels I see there is a slight shift (less than a pixel). I need to be able to overlay these products so that a pixel in the DEM is completey coincident with an underlying pixel in the orthomosaic. I have tried several different settings but shifting occurs no matter what. I would think they should be spot on considering they generated from the same source.  Is there something I'm missing?

General / photomosaic swirled blurring or distortion
« on: August 21, 2019, 09:14:49 PM »
I have a question about something I see in a lot of the mosaics we have constructed using GoPro Hero photos as source imagery.  When zoomed pretty far in I notice areas where a sort of blurry swirling distortion happens. I have attached a screen shot of an example of this.

Can anyone shed some light why this happens and is there a way to reduce it?

Is it related to clarity of the photos or maybe the orthorectification process?

General / Is External GPU an good way to increase performance?
« on: May 29, 2019, 12:15:02 AM »
I asked my IT department to upgrade the GPU on the computer we use for SfM work. They agreed but want to add an external GPU instead of a better internal graphics card.  So I am wondering:

1. Is external GPU a good way to increase performance?
2. Are there any external GPUs that are known to work well with Metashape?

3. Conversely, are there any external GPUs to stay away from?

General / Digital elevation models - why are there have negative heights?
« on: February 21, 2019, 04:23:33 AM »
Hello, I am a little confused why the DEMs I generate have negative values? See attached example where the height ranges from 1 meter to -4.58 meters. Is it because photoscan picks an arbitray point and then every thing is either above or below that point?  Would it be wrong to add 4.58 to all values?   Thanks for any help on this!

General / Incorrect alignment problem
« on: September 12, 2018, 06:04:44 PM »
Hello, please see the attached screen shot to see what I am trying to describe here. In terms of numbers of photos aligned I got great alignment, but unfortunately part of it is inaccurately aligned.

I am wondering what is causing part of the sparse cloud to get tilted at about a 90 degree angle from the rest of the cloud? This is an underwater seafloor and is very flat, so the whole thing should be flat.  Any ideas on how to fix this? 

The images were captured from an underwater video that was taken back in 2016, so there is no EXIF or any sort of lat/longs.  Unfortunately I could not find out the type of video camera used, but I think it was a GoPro.


I have been working on a project to map out a coral reef plot. In the plot we have ground control points with known distances which were recorded into PhotoScan. So the scale in the DEM that PhotoScan created goes from -1.03 meters to 1.22 meters (see attached pdf of the DEM).

I am wondering why the negative baseline? 

My wild guess is that since I could not tell PhotoScan what the lowest point is, then PhotoScan just arbitrarily picks a starting point and measures everything up or down relative to that point? Is that correct or is something else going on?

If anyone could shed some light on this I would greatly appreciate it!


My photos do not have EXIF data, but I do have four ground control points with known lat/longs.  So should I do the Photo Align step first and then add in Markers with lat/long info, or should I add the Markers and lat/longs to the photos first before I do the initial alignment? 

I am new at this so please any help appreciated! Thanks.

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