Jordi, Thanks very much. I get it.
Best wishes. Wei 2015-03-09 12:52 GMT+00:00 Jordi Inglada <[email protected]>: > [email protected] wrote: > > > > Hello, > > > > Does anyone could confirms it ? > > > > On Friday, March 6, 2015 at 3:35:05 PM UTC, [email protected] wrote: > > > > Thanks, Jordi, > > > > Now I am running the CloudDetectionExample, and my goal is to > > adapt this method to detect the cloud automatically, which is mean > > that i should combine the classification method and spectral angle > > together. > > > > My first problem here is that: what exactly the referencePixel > > mean? > > I have found one reply from a discussion several months ago which > > said:"pixel components parameters are a pixel value in the input > > image taken on a cloud which is used as a reference for spectral > > angle computation".So whether the "a pixel value" is the DN > > (Digital Number) Value of the specified pixel? Just because there > > are 4 bands, so the values have 4 components, Is that right? > > > > If the image only have 3 bands (Like RGB colorful images, and such > > kind of images are more normal and available that tiff with four > > bands), So I only need to provide 3 components of a cloud pixel, > > Is that right? > > > > Best wishes! > > Hi, > > The reference pixel is the one with which every pixel in the image would > be compared using the spectral angle. > > If you use the example in OTB, it assumes that the input image has 4 bands > and therefore it takes 4 values as spectral bands. > > > VectorPixelType referencePixel; > referencePixel.SetSize(4); > referencePixel.Fill(0.); > referencePixel[0] = (atof(argv[5])); > referencePixel[1] = (atof(argv[6])); > referencePixel[2] = (atof(argv[7])); > referencePixel[3] = (atof(argv[8])); > cloudDetection->SetReferencePixel(referencePixel); > > You can modify the example to use as many bands as your input image has. > > Jordi > > > > > On Friday, March 6, 2015 at 12:53:42 PM UTC, Jordi Inglada wrote: > > > > [email protected] wrote: > > > > > > Thanks very much for your reply,Jordi. > > > > > > I have read the first paper, it need cloud and cloud shadow > > match, and > > > the processing was more complicated than OTB. > > > > > > As refer to OTB cloud detection method,I have another > > question:the OTB > > > cloud-detect method need specify a pixel which possibly is > > cloud, that > > > means it can not recognize cloud automatically.If someone > > adopt the > > > OTB cloud detection method to process large amount of images > > or run > > > real-time on-board the remote sensing satellite, Obviously, > > one can > > > not pick a cloud pixel for the OTB program.So my question > > is: > > > > > > Does there any techniques to determine the reference cloud > > spectral > > > angle automatically? Or could I just preset the reference > > cloud > > > spectral angle? > > > > > > I know that some methods such as SVM could train the cloud > > spectral > > > angle classifier which could act as a reference，Any other > > > suggestion?? > > > > > > > Hi, > > > > I simple approach for which I have seen good results is indeed > > supervised classification. If you can generate a set of > > training samples (small polygons) for the cloud and for the > > non-cloud classes, you can use either SVM or Random Forests to > > implement your cloud screening procedure. > > > > In this case, you don't even have to code in C++ and you can > > use the OTB applications. Have a look here: > > > https://www.orfeo-toolbox.org/CookBook/CookBookse14.html#x66-1010004.4 > > > > > > Good luck. > > > > Jordi > > > > > Thanks again! > > > > > > On Thursday, March 5, 2015 at 12:37:58 PM UTC, Jordi Inglada > > wrote: > > > > > > [email protected] wrote: > > > > > > > > Hello guys, > > > > > > > > Now I am a beginner to use the OTB and I have some > > problems when > > > using > > > > the Cloud Detection Example. > > > > > > > > As far as I know that there are several techniques to > > detect > > > cloud > > > > from the remote sensing imagery. In the OTB, it detects > > the > > > cloud > > > > based on spectral angle principle and assume that the > > image have > > > four > > > > spectral bands. In my mind the parameter setting should > > affect > > > the > > > > detection result, and the parameters must set according to > > > Sensor that > > > > the camera adopted.But not every cameras have four > > spectral > > > bands. > > > > > > > > So My questions are: > > > > > > > > Does there any papers about the OTB Cloud Detection > > method? > > > > > > > > Does it work well using only three spectral band? > > > > > > > > What is the basic principle to set the parameters? > > > > > > > > Anyone any suggestion is welcome! > > > > > > > > Thanks very much. > > > > > > > > -- > > > > > > Hi, > > > > > > You are right about the fact that there are many methods for > > the > > > detection of clouds. The spectral method proposed in OTB is > > a very > > > simple one (spectral angle and low-pass filtering before > > > thresholding), but has the advantage of not needing any > > particular > > > spectral band (SWIR or thermal, for instance). > > > > > > If you want more sophisticated approaches, you should try to > > > implement something inspired from Fmask[1] for single-date > > > acquisitions or from MACCS[2] for multi-temporal series. > > > > > > Jordi > > > > > > [1] Zhu, Zhe, and Curtis E. Woodcock. "Object-based cloud > > and > > > cloud shadow detection in Landsat imagery." Remote Sensing > > of > > > Environment 118 (2012): 83-94. > > > > > > [2] Hagolle, Olivier, et al. "A multi-temporal method for > > cloud > > > detection, applied to FORMOSAT-2, VENµS, LANDSAT and > > SENTINEL-2 > > > images." Remote Sensing of Environment 114.8 (2010): > > 1747-1755. > -- -- Check the OTB FAQ at http://www.orfeo-toolbox.org/FAQ.html You received this message because you are subscribed to the Google Groups "otb-users" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/otb-users?hl=en --- You received this message because you are subscribed to the Google Groups "otb-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
