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Author Topic: Tetracam multispectral imagery processing  (Read 30016 times)

Ben1

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Re: Tetracam multispectral imagery processing
« Reply #15 on: September 22, 2013, 10:42:22 PM »
Thank you martin from geo-konzept germany for helping me with combining the agrisoft and the Tetracam adc lite and solving issues in remote sensing , helping solve problems can save me a tremendous time and effort in my project.

danitena

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Re: Tetracam multispectral imagery processing
« Reply #16 on: September 26, 2013, 11:46:46 PM »
I follow those steps and only one band apears in agisoft  and very bad results when processing ADC images.

What I am doing wrong?

Thanks



Hello ricardo9856,

Please check pre-processing instruction for TetraCam multispectral imagery processing: http://downloads.agisoft.ru/pdf/Tetracam%20multispectral%20imagery%20processing.pdf

After the multipage TIFF files are prepared you can load them to PhotoScan Pro. The workflow is similar to common photos processing, but for multiband data you need to select Master Channel first (from context menu by right-clicking on the chunk label in the Workspace pane). All the following processing steps will be applied to the master channel (camera positions will be estimated based on the master channel data and geometry will be reconstructed accordingly).
But when you use Export Orthophoto command the resulting TIFF file will contain all the original layers (bands).
We recommend to use 0.9.1 pre-release for multipage TIFFs.

However, we've faced problems with aligning the ADC lite imagery caused by long rolling shutter time used for specific datasets.

STINCHI

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Re: Tetracam multispectral imagery processing
« Reply #17 on: June 29, 2014, 12:28:52 PM »
Hello to everybody.
I would like to know the community comments ( Riccardo's one especially   8) ) about Martin's answers.
I am thinking to buy a drone+tetracam system for vineyard monitoring............. ::)
Thank you very much in advance for your replies.
Regards

HyperFox

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Re: Tetracam multispectral imagery processing
« Reply #18 on: July 02, 2014, 12:13:38 PM »
Dear Martin,

it is as it is, the tetracam has a rolling shutter. Any movement of a pamera platform will distort the image.

If your camera platform is moving fast (plane?), you will get a somewhat "stretched" image in one direction (e.g. y - axis of image coordinate system) and a very small distortion in the other direction (e.b. x axis). And PhotoScan will handle that different image scale in x and y within the camera calibration. That why some datasets look "good".

They also look "acceptable" in some cases due to the low resolution of that camera.

But just take the ADC in your hands, sit down on an office chair, rotate yourself slowly and hold the adc 50 cm away from your breast (z-axis). You'll never get undistorted images.

It's not an issue of "low cost uav", it's an issue of CMOS...

Best regards
Ansgar


Hi Community,

today was helping a member of this community with his ADC data. I had no Problems to create a perfect Ortho Mosaik with Agisoft PhotoScan.

Attached some Screen shots showing the steps ...

@AngarG: No rolling shutter :-) 

Again: If some others of you need my help with ADC data, please get in touch with me !

Cheers
Martin

gEEvEE

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Re: Tetracam multispectral imagery processing
« Reply #19 on: July 04, 2014, 02:57:28 PM »
Hi All,

the only solution to do low-cost multispectral imaging at high spatial resolutions is to use two reflex or mirrorless cameras. Whatever LDP LLC (MaxMax) or other companies claim, the current Bayer patterns that cover the silicon sensor make it impossible to create a decent (i.e. spectrally pure) NIR - Red - Green camera.

Some years ago, such an approach was tried by the Eastman Kodak Company with their now discontinued Kodak DCS-200 CIR, DCS-420 CIR and DCS-460 CIR. Although their spectral response approximately matched Kodak’s NIR-sensitive emulsions, both these film emulsions and these digital cameras acquired spectral information in very broad wavebands, hence taking significant portions of the other spectral bands into account: the red sensitive photosites (and to a lesser extent also the green channel) take large portions of the NIR into account, a drawback Kodak counteracted by subtracting the NIR’s Digital Numbers (DNs) from the initially captured green and red DNs. However, this approach could never yield pure spectral information.

Because the spectral response curves do not even coincide on the long wavelength side, it is impossible to remove the precise NIR-contributing part of the green and red channel. Moreover, the NIR and red channel still took a significant portion of the red edge region into account, which made these broad band imagers less suitable for quantitative spectral analysis as they masked unique spectral features to a large extent. As also the analogue media were characterized by a low spectral fidelity, Kodak’s NIR-enabled digital cameras emulated the Kodak CIR film rather well, and were therefore often used in several vegetation studies.

Current digital sensor do, however, suffer from the same spectral overlap (see the figure of a bare Nikon D80 sensor that I measured several years ago). A two-camera system based on a NIR-modified with an unmodified camera can, however, deal with these issues. In this solution, the spectral fidelity of the acquired information is, obviously, superior to the CIR film and any current, full-spectrum modified camera.

A possible solution to capture CIR imagery with only one DSC was presented in the United States patent 20060066738, in which Hershey and Zhang proposed a Colour-Filter Array pattern consisting of four different coloured filters, three passing the blue, green and red visible bands, while a fourth is dedicated to transmit pure NIR or UV radiation. It is, however, highly questionable whether any company will ever market such a device, in which case a multispectral imaging system utilizing a multitude of cameras would still offer a higher resolving power and more possibilities in choosing spectral combinations.

Cheers,
Geert