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Author Topic: Analyze what is wrong with my historical aerial imagery mosaics  (Read 2807 times)

aggieair

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Analyze what is wrong with my historical aerial imagery mosaics
« on: December 08, 2015, 09:59:03 PM »
We are in the middle of a historical aerial imagery project where we scanned in paper maps at 1200 dpi.  No referenced data is known, but we pulled XYZ values from LiDAR bare earth and intensity rasters.

It's been a challenge to say the least adding the "right" arrangement of points without it blowing up. 

Anyway, some mosaics will turn out OK and others will have some issues (see attached). 

Is this mostly because I am using the standard DSM (aka all points) to create the mesh and not a DTM? It would be pretty impossible to classify ground points for a DTM with these forested scenes.  I've also been using the LOW or MEDIUM point cloud density quality so that I get a well distribution of points even up in the trees.  HIGH and ULTRA will leave lots of gaps which affects the mosaic.
« Last Edit: December 09, 2015, 12:48:34 AM by aggieair »

aggieair

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Re: Analyze what is wrong with my historical aerial imagery mosaics
« Reply #1 on: December 10, 2015, 12:43:36 AM »
From Agisoft:

The issues that you are observing on the orthomosaic might be related to the low number of polygons in the area of interest. Even when you are using High face cont option, the could be areas with small polygons (related to the trees and greenery, for example) and big polygons (on the roads or bare ground).

Additionally we would like to inform you that version 1.2.0 has been released recently and it allows to generate DEM based on the dense cloud itself, so the issues the large polygons can be avoided:
http://www.agisoft.com/downloads/installer/


This was the trick.  We were just about to create the mosaics in an external software using the LAS points as a last resort.  Now it can be done in Agisoft!

Alexey Pasumansky

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Re: Analyze what is wrong with my historical aerial imagery mosaics
« Reply #2 on: December 10, 2015, 01:07:58 AM »
Hello aggieair,

So were the project results better for DEM-based orthomosaic?
Best regards,
Alexey Pasumansky,
Agisoft LLC

aggieair

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Re: Analyze what is wrong with my historical aerial imagery mosaics
« Reply #3 on: December 10, 2015, 02:26:08 AM »
Yes, much better!  No more shards of glass issues :)

When zoomed to full extent in ArcGIS, the new DEM derived mosaics appear "softer" or not as sharp as the previous mesh-derived mosaics.  But then upon zooming in and checking the pixel size, they are nearly the same.

Sorry I have not made any dense point cloud screen shots for you yet...

I am working on comparing the new DSM rasters now derived from point clouds...

We were just about the export the points to Global Mapper and to this externally. Phew!