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Author Topic: Urgent help needed - Ridge lines in DSM/DEM export  (Read 5409 times)

Alexey Pasumansky

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Re: Urgent help needed - Ridge lines in DSM/DEM export
« Reply #15 on: February 21, 2018, 11:58:41 AM »
Hello Pkroks,

If the same artifacts can be reproduced, when processing only two flights together, I can suggest to try running the alignment for such smaller dataset with the disabled pre-selection and check if any valid matching points are found in the area of overlap.
Best regards,
Alexey Pasumansky,
Agisoft LLC

Pkroks

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Re: Urgent help needed - Ridge lines in DSM/DEM export
« Reply #16 on: February 21, 2018, 07:42:40 PM »
Hello Pkroks,

If the same artifacts can be reproduced, when processing only two flights together, I can suggest to try running the alignment for such smaller dataset with the disabled pre-selection and check if any valid matching points are found in the area of overlap.

Hi Alexey,

I reprocessed the entire data set with no GCPs or markers, on medium alignment, medium dense cloud and mild depth filtering.

The DSM ridges are improved in the initial area, but have moved to another area that had no issues before.

I will try to process the area in chunks separately on medium, only with reference pre-selection on, not generic.

Pkroks

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Re: Urgent help needed - Ridge lines in DSM/DEM export
« Reply #17 on: February 22, 2018, 08:27:06 AM »
Hi again Pkroks,

You could try to run photo alignment on ALL images (choose quality setting MEDIUM unless you have a high-end computer) to see if the ridge problem persists (also use your GCPs). For the dense point cloud you would then divide your project into several chunks (using a Python script) and then merge all chunks at the end for the final product (unless you have a high-end computer/multi-GPU setup that can compute a dense point cloud from over 4,500 images).
In some areas where aerial surveys overlap (as seen in your processing report) you could even disable a few images to speed up processing.

Regarding settings for your camera. Many people use manual focus set to infinity (when flying high above the ground) because autofocus might a) be too slow which means the picture is not taken where it should be taken and b) might simply get it wrong (leading to out-of-focus/blurry images).
Use ISO 100 or 200 (if necessary even 400), shutter priority or manual and set your aperture to f/6.3 or f/7.1 (which is generally OK because you don't want to 'suffer' shutter speed-wise; remember the exposure triangle). These are the settings I commonly use on my Sony Nex 7 and A6000 (attached to a multi-rotor though).

If you shoot fully manual, adjust your aperture/shutter speed/ISO by using the live histogram on your camera. When working outdoors it is hard to tell on the tiny screen of your camera if the picture is properly exposed or not, but it is easy to see in the live histogram.

Last but not least, DON'T use the automatic white balance, but manually set it to cloudy or sunny (depending on the weather/light conditions).

All the best.

Regards,
SAV


Hi Sav,

Please can you share or help with the python script to split and then merge after the dense cloud processing. The system is as follows:
Intel i7 8700k 3.7ghz
32gb ddr4 ram 2400mhz
nVidia GTX1070 8gb
samsung 850 evo 250gb ssd
1tb seagate sshd harddrive.

Pkroks

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Re: Urgent help needed - Ridge lines in DSM/DEM export
« Reply #18 on: February 24, 2018, 09:14:01 AM »
Hello Pkroks,

If the same artifacts can be reproduced, when processing only two flights together, I can suggest to try running the alignment for such smaller dataset with the disabled pre-selection and check if any valid matching points are found in the area of overlap.

Hi Alexey,

I have managed to process the project in Two areas, one is about 995ha and the other about 800ha. There are no ridge lines in these two areas, however there is a ridge where they join. A variation of approximately 3-4m.

Any tutorial or links on a way to merge the two files now?

Thanks for the help. Very weird how it processes fine in two halves, yet as a complete project it gives ridges.. ??


SAV

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Re: Urgent help needed - Ridge lines in DSM/DEM export
« Reply #19 on: February 24, 2018, 10:02:08 AM »
Hi Pkroks,

You can find the Python script here:
https://github.com/agisoft-llc/photoscan-scripts/tree/master/src

Regards,
SAV

Hi again Pkroks,

You could try to run photo alignment on ALL images (choose quality setting MEDIUM unless you have a high-end computer) to see if the ridge problem persists (also use your GCPs). For the dense point cloud you would then divide your project into several chunks (using a Python script) and then merge all chunks at the end for the final product (unless you have a high-end computer/multi-GPU setup that can compute a dense point cloud from over 4,500 images).
In some areas where aerial surveys overlap (as seen in your processing report) you could even disable a few images to speed up processing.

Regarding settings for your camera. Many people use manual focus set to infinity (when flying high above the ground) because autofocus might a) be too slow which means the picture is not taken where it should be taken and b) might simply get it wrong (leading to out-of-focus/blurry images).
Use ISO 100 or 200 (if necessary even 400), shutter priority or manual and set your aperture to f/6.3 or f/7.1 (which is generally OK because you don't want to 'suffer' shutter speed-wise; remember the exposure triangle). These are the settings I commonly use on my Sony Nex 7 and A6000 (attached to a multi-rotor though).

If you shoot fully manual, adjust your aperture/shutter speed/ISO by using the live histogram on your camera. When working outdoors it is hard to tell on the tiny screen of your camera if the picture is properly exposed or not, but it is easy to see in the live histogram.

Last but not least, DON'T use the automatic white balance, but manually set it to cloudy or sunny (depending on the weather/light conditions).

All the best.

Regards,
SAV


Hi Sav,

Please can you share or help with the python script to split and then merge after the dense cloud processing. The system is as follows:
Intel i7 8700k 3.7ghz
32gb ddr4 ram 2400mhz
nVidia GTX1070 8gb
samsung 850 evo 250gb ssd
1tb seagate sshd harddrive.