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Author Topic: How To Dummy Down Exports? Reduce Points  (Read 3369 times)

jazzyj

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How To Dummy Down Exports? Reduce Points
« on: January 24, 2018, 10:43:27 PM »
I'm testing Photoscan with a project that is 1,600 photos (about 125 acre area) and I'm needing to export for someone to use the output in CAD software (DXF).  I recently installed QGis to see how the files come in.  The 3D Model export is 500MB file size and when QGis renders it, it's of course a gazillion points.  What if I don't need that level of detail in my exports, what is the settings I need to play with to reduce the number of points in the export.  Is it the Precision setting in the export?

The point cloud export is 11GB in size!  It was processed at the Medium setting.  So do I have to go back and reprocess as a lower setting or can it be reduced in export?

To be honest, I have no idea if an 11GB point cloud file (DXF) is going to make most CAD stations choke or is that not that big?
« Last Edit: January 24, 2018, 11:02:37 PM by jazzyj »

ThomasL

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Re: How To Dummy Down Exports? Reduce Points
« Reply #1 on: January 25, 2018, 04:58:46 AM »
Hi jazzyj,

I would also like to hear some insights from users on this topic.

What I would normally do is generate satisfactory DTM (trees and irrelevant objects removed), and then export it either as Geotiff (can be used as grid) or XYZ format. This exporting process allows you to drop the file size and number of points by setting a bigger spacing.

Also I would think if you go back and drop the quality setting of your dense point cloud generation it might affect the accuracy of your model.

Hope this helps!

Cheers,
Thomas

jazzyj

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Re: How To Dummy Down Exports? Reduce Points
« Reply #2 on: January 25, 2018, 07:05:00 AM »
So from my understanding the only way to reduce the points is to reprocess the dense point cloud with a different setting.  I used Medium.  This is for 4,000 photos shot at about 1inch/pixel GSD over a 250-acre area that is pretty flat (farm plot with maybe 25 feet max elevation change from lowest to highest point). 

I used that GSD because I didn't have ground control points and wanted to get the best X/Y measurement accuracy.  Now I'm just learning but it seems to me in a case where you have a very good GSD over a very large area that is fairly flat, you really shouldn't need a very dense point cloud.  The application for this project is to bring the data into a CAD system to aid in designing a sprinkler system for the land.

Am I wrong that Low would be a more appropriate setting than Medium for this type of job?

Apavlicek

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Re: How To Dummy Down Exports? Reduce Points
« Reply #3 on: August 08, 2018, 06:01:44 AM »
Were you able to lower the amount of point or the exported file size?

Alexey Pasumansky

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Re: How To Dummy Down Exports? Reduce Points
« Reply #4 on: August 08, 2018, 02:41:08 PM »
At the moment there's no option to decimate the dense cloud in PhotoScan. As an alternative to the cloud re-building using lower quality setting I see only exporting the cloud to the external application, like CloudCompare, filter the points there and import the dense cloud back to PhotoScan, if necessary.
Best regards,
Alexey Pasumansky,
Agisoft LLC

SAV

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Re: How To Dummy Down Exports? Reduce Points
« Reply #5 on: August 09, 2018, 04:39:40 AM »
Hi jazzyj,

Here are the details on how to reduce the number of points in a point cloud using CloudCompare (free, open source).
https://www.cloudcompare.org/doc/wiki/index.php?title=Edit%5CSubsample

Regards,
SAV