Mr.Mountain's profile - activity

Hello,

I was trying to use the Features from Accelerated Segment Tests (FAST) with a descriptor in OpenCV 2.4.3 C++. But every time I try to match the computed descriptor-matrices I'll get an confusing error. I tried to investigate the source-code but I can't see why this assertion fails.

OpenCV Error: Assertion failed (trainDescCollection[iIdx].rows < IMGIDX_ONE) in knnMatchImpl, file C:/slave/WinInstallerMegaPack/src/opencv/modules/features2d/src/matchers.cpp, line 365

Here's some example-code to run. The images are already loaded.

Mat* fstImageDescr = new Mat;
Mat* sndImageDescr = new Mat;
vector<cv::KeyPoint> fstKeypoints, sndKeypoints;

FastFeatureDetector *fastDete = new FastFeatureDetector;
SurfDescriptorExtractor* surfDesc = new SurfDescriptorExtractor;

fastDete->detect(*fstImage, fstKeypoints);
fastDete->detect(*sndImage, sndKeypoints);
surfDesc->compute(*fstImage, fstKeypoints, *fstImageDescr);
surfDesc->compute(*sndImage, sndKeypoints, *sndImageDescr);

vector<DMatch>* matches = new vector<DMatch>;
BFMatcher *matcher = new BFMatcher(NORM_L2);
matcher->match(*fstImageDescr, *sndImageDescr, *matches); //CRASHES

Thank you for your help.

Hello, I'm trying to use the SIFTFeaturesDetector with an ORBDescriptorExtractor in C++. The images are loaded in colour. But I guess that doesn't matter since they would be converted by the detector/descriptor ?

SiftFeatureDetector sift;
sift.detect(fstImage,fstKeypoints1);
OrbDescriptorExtractor orbDesc;
orbDesc->compute(fstImage, fstKeypoints1, fstImageDescr);

This causes a bad_alloc coming from the vector of the keypoints. Im using 2.4.3 and can't tell why this is happening. When I'm trying to use ORB with a SIFT-Descriptor the system crashes completely. Do I miss something?

UPDATE: Found one issue: http://code.opencv.org/issues/2521#note-2 Perhaps a second one should be opened ... or I was wrong and everything else is fine.

Thank you. =)

I found out that besides of RANSAC/LHS or something else the estimation of the homography always needs at least four points.

Hello, I'm currently finishing my evaluation-tool for interest point detectors. In the last steps I found a confusing error.

Mat findHomography(InputArray srcPoints, InputArray dstPoints, int method=0, double ransacReprojThreshold=3, OutputArray mask=noArray() )

The srcPoints and dstPoints are vector<points2f> which stores the corresponding points of the matched keypoints. So far nothing special - It's like in the tutorials.

But when I use RANSAC and have a vector<Points2f> in range [0, ... , 4[ I get an assertion error than the counter should be greater or equals four.

Question 1: Does the algorithm needs at least four points to describe what belongs to the current model or not and to create the consensus ?

Question 2: Is there any documentation about this? (I took a look at the doc and the tutorials.)

Thanks for your help.

If I have several images and train a FlannBasedMatcher with theirs descriptors, will there only be on DMatch for every keypoint of the queue-image?

Open up the example and look at the imports. The package will describe where it is located. If it is a standard Java API class then you should copy the import into your class where you use the rectangle.

If the import has a different package, try to locate the library with this class. Copy the library into a folder. If you use Eclipse click right onto the lib and select "add to build path".

If none of this solutions worked, please give us more information. Perhaps a snippet of the example file.

Hello, I'm currently working on a small application which should index some images and store this index. I'm reading the image and getting the keypoints. For writing down the data I would use yaml.

vector<cv::KeyPoint> keypoints;
cv::Mat source = cv::imread("test.jpg");
Ptr<FeatureDetector> detector = new SurfFeatureDetector(400);
detector->detect(source , keypoints);


Now I have the keypoints. This is the first possible move to save the keypoints, If I do so, I can complete reconstruct any keypoint found. So no problem.

But what I want is to store the descriptor. So lets go a little bit further:

cv::Mat sourceMatch; Ptr<DescriptorExtractor> descriptorExtractor = new SurfDescriptorExtractor();
descriptorExtractor->compute(source , keypoints, sourceMatch);
Ptr<DescriptorMatcher> matcher = new BFMatcher(NORM_L2);


At this Point I'm not sure if I could save down the descriptor to the yaml-file. Any idea? I could try to save down the matcher. But this won't work:

vector<Mat> descriptors;
descriptors.push_back(sourceMatch);
matcher->train();
FileStorage* fileStorage = newFileStorage("index.yml",FileStorage::WRITE, "UTF-8");
matcher->write(*fileStorage);

This statement only saves me a yaml file with the header. And as I would guess even if I could write down the matcher I wouldn't write down the consisting descriptors. Has anyone an idea how to save the descriptors?

thanks