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VLFeat open source library does not return structure Fq consisting of ellipsoids descriptors and gives error message ??? Attempt to reference field of non-structure array.

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I am working on an image retrieval project. It requires The VLFeat open source library which implements popular computer vision algorithms specializing in image understanding and local features extraction and matching. Even after successful implementation of VLFEAT toolbox I get the following error:
??? Attempt to reference field of non-structure array.
Error in ==> gm at 84 locs = fq.f(1:2,:);
fq is a struct with the N query features as returned by VLFEAT: contains of two elements: 1.- fq.f is a 6xN matrix with the ellipsoids descriptors of each detected feature in the query. 2.- fq.d is a MxN matrix with the M-dimensional features descriptors of each detected feature in the query.

Accepted Answer

Dima Lisin
Dima Lisin on 8 Apr 2015
It looks like fq is not a struct. Put a breakpoint at that line, and see what it is. My guess is that it may be empty.
Sushant Hiwale
Sushant Hiwale on 10 Apr 2015
function [frames, descrs] = getFeatures(im, varargin)
opts.method = 'hessian' ;
opts.affineAdaptation = false ;
opts.orientation = true ;
opts.peakThreshold = 28 / 256^2 ;
opts = vl_argparse(opts, varargin) ;
if size(im,3) > 1, im = rgb2gray(im) ;
end im = im2single(im) ;
[frames, descrs] = vl_covdet(im, ... 'AffineAdaptation', opts.affineAdaptation, ... 'Orientation', opts.orientation, ... 'FirstOctave', 0, ... 'FloatDescriptors', ... 'Method', opts.method, ... 'PeakThreshold', opts.peakThreshold, ... 'Verbose') ;
frames = single(frames) ;

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