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Feature Detection

dave hoeffgen

dave hoeffgen

Resource contributor
Messages
1,439
Country
germany
Hello,

Not sure if this was asked before but I just got back into the process of detecting features (vegetation so far) from aerial imagery.
From earlier versions of scenProc's Texture filter editor I was used to specifying color values and standard deviation to detect the desired feature.
I read the manual about the filter nodes and also the examples, but sadly my data does not come with a NIR channel required for a reasonable NDVI conversion.

As I can't seem to get a node setup doen that highlights the right areas in the image I would like to ask if somebody can help me figure this out. Am I missing something?

Regards,
David
 
Hi David,

With the new texture filter editor there are two options:

1. You could try the back project step. With this step you select some areas in the photo of the feature you want to detect and the detection will then find similar areas.

2. You can also make a texture filter that selects based on the color and standard deviation values. The steps for that are available.

I guess it would be good if I added some samples for these options to the manual as well. Maybe we can define some filter together that works for you and then I can use it in the manual as well. Would you have a sample of the kind of images you work with and also some more information on the flow you used before? Then I can make a sample for you.
 
I just tried the back project step, assuming I am supposed to just pass the input image through the back project node and into the output image, make the samples as described in the manual and end up with a similarity map.
Sadly that didn't work and the output image remained black. also I noticed when I pan and zoom to a certain area to make a sample the sample I end up does not look like the location I selected.

The last time I used feature detection is years ago and I used the histogram workflow as you described in your 2013 youtube video. I'm attaching a sample of the imagery, especially the trees in urban areas are what I need to detect as they are not featured in OSM data.
 

Attachments

Thanks, I'll try to make a sample based on that image.

You should not zoom and pan when you use the back project step. Then the selection doesn't work right indeed.
 
Hi,

Sorry, it took a while before I had the time to look at creating the sample. But I think you have found a bug, because I can't make the back project working with your image as well. I need to check the code why this is happening.
 
Hi,

I can confirm it's a bug. The back project step that uses histograms to match areas seems to have an issue when there are 3 channel or a blank alpha channel. I'm trying to fix that now.
 
Hi,

I have fixed the bug in the back project step. But I need to tune the example script a bit more to get it working. So that might take a few more days,
 
I really appreciate all the work you put into this tool and the effort to support us with every little issue.
I can't thank you enough
 
Hi,

I have added a new sample texture filter in the manual now. I have attached the file to this post as well.

It works reasonably on your image, although in some areas a tree is missed or some grass is picked up. But with only a colour image it is hard to get it perfect.
 

Attachments

arno said:
Hi,

I have added a new sample texture filter in the manual now. I have attached the file to this post as well.

It works reasonably on your image, although in some areas a tree is missed or some grass is picked up. But with only a colour image it is hard to get it perfect.
Click to expand...

Thanks a lot!

I will take a look at it tomorrow.
 
Thanks again for the sample and the new explanation in the manual.
After trying it in the current scenProc version it worked for me
 
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