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### Messages - Thibaud Capra

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1
##### General / Ground filtering algorithm: where does it start?
« on: May 23, 2017, 03:42:59 PM »
Hello,
I've been using the ground filtering algorithm with great success so far but I was wondering how accurate it was. I ran a few tests using sample data and creating confusion matrices, comparing the results with state-of-the-art algorithms to assess his performance. So far so good.

As a student doing his masters thesis, I'd love to know a bit more about how it works. I understand, as a commercial licence, that I won't get much, but it's worth a try!

In the User Manual, it is written:
Quote
Max angle (deg)
Determines one of the conditions to be checked while testing a point as a ground one, i.e. sets limitation for an angle between terrain model and the line to connect the point in question with a point from a ground class. For nearly flat terrain it is recommended to use default value of 15 deg for the parameter. It is reasonable to set a higher value, if the terrain contains steep slopes.
Max distance (m)
Determines one of the conditions to be checked while testing a point as a ground one, i.e. sets limitation for a distance between the point in question and terrain model. In fact, this parameter determines the assumption for the maximum variation of the ground elevation at a time.
Cell size (m)
Determines the size of the cells for point cloud to be divided into as a preparatory step in ground points classification procedure. Cell size should be indicated with respect to the size of the largest area within the scene that does not contain any ground points, e. g. building or close forest.

• Where is the algorithm starting? Most algorithms assume the lowest point is a ground point and start from here. Is it the same case here?
• I guess it deals with outliers using a combination of two criterion: Max Angle & Max Distance. But what if the lowest local point happens to be an outlier? Do you run some kind of SOR filter prior to the lowest point picking?

2
##### General / Re: About "Build Orthomosaic"
« on: May 05, 2017, 04:28:12 PM »
Hello Alexey,

Thanks for the help, I'll try the 1.1.0 version and see if it works.

3
##### General / Re: About "Build Orthomosaic"
« on: May 05, 2017, 12:55:44 PM »
Hello Alexey,

I assume this wonderful script doesn't exist in 1.2.6?

That might be the problem. If I draw my shapes, then convert them to the same coordinates system, would it work? Or do I have to change the projection beforehand?

4
##### General / Re: About "Build Orthomosaic"
« on: May 05, 2017, 11:59:14 AM »
Hello Alexey,

I've been thinking about masking, but inspecting 1400 photos is pretty time consuming. Can I generate masks based on color or something similar? Usually these people wear pretty bright colors!

As for the seamline editing, I can draw a polygon, but when it comes to the image selection, I cannot access it whatsoever.

5
##### General / Re: About "Build Orthomosaic"
« on: May 05, 2017, 11:34:52 AM »
Hello Alexey,

As these orthos are a result from an automated process using Python scripting, we aim at obtaining orthos that look as good as possible fresh out of the pipeline.
We're going for the mosaic blending mode, then a quick editing for now, because it's shorter than average blending mode editing to rectify the color (note that the one I linked had the Color Correction enabled)

Assign Image is also a manual process, am I right?
Another problem, our processing areas are quite small, only small parts of a 75-hectares area covered by 1400 photos at 90m flight height, so seamline editing doesn't work. Any reason for it? Is it because the generated orthomosaic used the bare minimum of photos?

6
##### General / Re: Most effective way to create survey site plans using photogrammetry?
« on: May 05, 2017, 10:49:28 AM »
As a surveyor (hopefully in september I'll have my diploma!), I'd use photogrammetry to do surveys in very specific cases.
For facade surveys, a great way is obviously using orthophotos to have a quick plan of it.
As for sites, you already mentionned the masking issue and Jeremiah is right saying that vegetation and water may cause problems.

For facade surveys, I'd go for a mix of terrestrial and aerial photogrammetry, bearing in mind the rules.

TL;DR: Surveying site plans using photogrammetry is case dependant.

7
##### General / Re: About "Build Orthomosaic"
« on: May 05, 2017, 10:40:05 AM »
Hello Alexey,

I must've missed it in the manual, my bad.

Using the Mosaic blending, I see people in my orthophotos that are undesirable (leftmost part):

After some editing, I can get pretty decent results:

Using the Average blending, the same people are merely shadows (this area they are pretty static, but in others they are hidden), but I have issues with colors:

Ideally, I'm looking for a mode that'd combine Mosaic and Average to result in what I have after editing the orthophoto in photoshop.

8
##### General / About "Build Orthomosaic"
« on: May 04, 2017, 06:25:43 PM »
Hello everyone,

I'm using orthomosaics to texture external DEMs but I have an issue: some details seem to be kept when I'm using the "Mosaic Blending" option. If I use the "Average Blending" one, these details are blended in and are hidden, but I have weird color disparities.

Either way, to have a clean result, I need to either photoshop these tiny details out or correct the color saturation of my image.

Is there any way to have details about how each mode works?

Thanks.

9
##### Feature Requests / Re: Split the model view window into quad view
« on: May 04, 2017, 06:16:59 PM »
I agree with Jeremiah_ROWE, it would be very heavy on hardware with big models. Maybe limit the windows depending on hardware?
Great feature idea though, +1.

10
##### General / Re: DEM without GCPs and UAV?
« on: May 04, 2017, 05:42:21 PM »
I could be wrong, but since the grass I have in my landscapes have some kind of patterns from the mowing, I'd say matching and aligning photos is easier.
If your grass is a wild, dense one, I believe it's harder. Having distinctive items in your photos would greatly help IMO.
Not necessarily having a target visible in every photo, but at least 3 would be a good start.
Basically, if you have a decent overlap you should be good.

Keep in mind the 3x3 rules of Photogrammetry!

11
##### Feature Requests / Re: (Mesh Gen) - Disable Vertex Color gen
« on: May 04, 2017, 05:37:41 PM »
Agree, you can already export your mesh without colors but building it thus making it quicker is a good idea.

12
##### General / Re: DEM without GCPs and UAV?
« on: May 04, 2017, 05:32:17 PM »
Hello matt07lx,

I'm creating accurate 3D models of golf courses using UAVs, which are, well, mostly grass. Clear patterns would help building your model though: can you set up coded targets on your site?

13
##### General / Re: Opening psx files in another software
« on: May 04, 2017, 04:08:43 PM »
If you save your project in psz format, the latest CloudCompare version can open it!

14
##### Feature Requests / Re: While "Assign Images" to the OrthoMosaic
« on: May 04, 2017, 02:42:01 PM »
+1, obvious ergonomics!

15
##### General / Re: What GPU is better?
« on: May 02, 2017, 03:48:24 PM »
Depending on your PhotoScan's version, note that the image alignment is relying on CPU only (before 1.3), that could be misleading when examining the resources used.