Questions tagged [spatial]

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1answer
2k views

Understanding Spatial Frequency of Images (using matlab)

I wish to isolate a crosswalk from its surrounding, and I thought that as crosswalks have a repetitive pattern of thick white stripes, I might be able to isolate them by measuring their frequency ...
3
votes
2answers
127 views

Smooth 2D Data with Discontinuous and Artificial Jumps

I have some data $(X,Y,Z)$, which is a set of measurements $Z$ over a $2D$ space $X$,$Y$. The $Z$ data on this space is continuous except for some discontinuous jumps in certain domains of $X$,$Y$ (...
3
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0answers
241 views

Question on spatial sampling for non-linear and/or non-uniform arrays

I am a little confused as to how to compute the nyquist criterion for a sensor array that is not linear, and/or non-uniform. For the linear, uniformly spaced case, the spatial nyquist is delimited by ...
2
votes
1answer
34 views

Designing a sound that localises well

I am trying to create or find a sound that localises well. I read that emergency vehicles are changing their sirens; people found it difficult to localise the sound of the old siren (a sinusoidal ...
2
votes
2answers
128 views

Are there accepted ranges of “high”, “medium” and “low” visual spatial frequency?

I have an image and have been able to quantify its power across spatial frequencies, using Python. What I am interested in doing is creating some measure of how much of the image's information is low, ...
2
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0answers
50 views

Physical Interpretation of $\mathbf A$ beamforming Matrix

The directivity of an array is defined as: $$ D = \frac{1}{2} \int_{-1}^{1} \lvert B_{u}(u)\rvert^{2} du$$ Where $B_{u}(\cdot) = \mathbf{w}^{H} \mathbf{v}(\cdot) $ is the beampattern of the array in ...
2
votes
1answer
496 views

How to reverse frequency spectrum of a 2D image?

Reversing spectrum of an audio signal is said to be often used in DSP – i.e. applying a low-pass filter is quite a simple operation, compared to a high-pass. So they shift the specrtum by multiplying ...
1
vote
2answers
892 views

Getting HRTF from 3-D scan + acoustic simulation

This question follows from Modelling propagation of sound wave by particle simulation This last fortnight I have started experimenting with Binaural audio; it really blows everything else out of the ...
1
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1answer
3k views

What is spatial correlation and spatial convolution?

What does the term spatial correlation and spatial convolution mean with respect to digital image processing ?
1
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1answer
776 views

Spatial sampling frequency equation

Upon reading this microphone array tutorial, I'm stuck in the following piece: The spatial sampling frequency along the x-axis is given by $f_{x_s} = \frac{\sin \theta \cos \phi}{\lambda}$ ...
1
vote
1answer
803 views

What does PSD represent in the spatial domain?

People use FFT methods to analyze topographic features in the spatial domain, such that the signal varies over (x) rather than (t). If a PSD curve characterizes amplitude versus frequency of an ...
1
vote
1answer
212 views

Nyquist Criterion in higher dimensions

I was just wondering if there were any "obvious" resources, papers, or textbooks I should look into regarding the nyquist-criterion in higher dimensions. For example, this would be relevant if there ...
1
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0answers
179 views

How to calculate spectrogram from nonstationary, nonuniformly sampled signal

I have a high resolution 3D spatial signal (xy-elevation data collected via Terrestrial Laser Scan) with very nonuniform sampling (holes/shadows due to vegetation; point spread varies as a function of ...
1
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0answers
841 views

How to calculate the spatial frequency of an image in cycles per image

I have been attempting to calculate the spatial frequency of a colour image. I first converted it to grayscale and used a Fast Fourier transformation (fft2) that codes the quantity of each spatial ...
1
vote
1answer
801 views

How to find PSD (Power spectral density) of spatial data

I have profiled a surface, measuring the height of peaks and troughs at 0.02mm intervals. I have 1501 data points, the below listed as an example: $$\begin{align} x &= 0\,\mu\text m & y &...
1
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0answers
229 views

Spatial resampling, how to smooth?

Sorry if this is not the right forum. Having a velocity grid in which a wave propagates, and given a certain spatial sampling of the grid, what kind of smoothing/interpolation should be used if the ...
0
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4answers
131 views

Signal and Space/Time

I have been reading a couple of definitions on signal such as: Any quantity measurable through time over space or any higher dimension can be taken as a signal. And this, In the physical ...
0
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2answers
83 views

Simulating spatial perception - with cosine wave based sound - in MATLAB

I'm trying to create cosine wave, one for the right channel and another for the left. The one on the left is to be moved in phase to simulate change to the spatial perception of the tone. A delay in ...
0
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2answers
360 views

Digital Panning Effect

To get a panning effect I know that there is a need for a Circular Matrix. The angle is can be set as a default or I can let the user to select the angle. So if the angle is $\theta$, the circular ...
0
votes
1answer
67 views

Difference between 'spatially' and 'instantaneously' independent

For a multivariate time series $$\underline{y}(t)=[y_1(t) \dots y_n(t)]^T$$ What is the difference between the components $y_i(t)$ being spatially independent and instantaneously independent?
0
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2answers
294 views

Calculating spatial width from power spectrum HWHM

Say I have a 1D (spatial) signal (resolution = $1000$) which is zero everywhere except from $x = 250$ to $750$, where it equals one. I ultimately want to calculate the spatial width of this signal ...
0
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2answers
255 views

IFFT of Microphone Array Directivity Response

I am implementing a microphone array simulation in my thesis. My prof and many documents indicates that microphone array behaves like filters in DSP but instead time-frequency domain there exists ...
0
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0answers
18 views

Multi channel signal enhancment inequality proof

Assume that $\mathbf{h}(f)$ is a spatial filter coeff vector, and $\mathbf{d}(f)$ is the steering vector. $\mathbf{\Phi_v}(f)$ is the correlation matrix of noise. How do i proof the following ...
0
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0answers
176 views

Use 2D FFT to replace 2D Discrete Fourier Transform (MATLAB)

I met a problem. I ran a code to implement the 2D discrete Fourier Transform, here is the code: ...
0
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1answer
137 views

How to prepare and plot unequally spaced, irregular data to a contour plot or similar with MATLAB

I've got a data set of hot-wire measurement velocity amplitudes at a given frequency bin (time data that has already been transformed to the frequency domain and I am just considering data for a given ...