How could I calculate the size of dots, height, and width of cylinder by pixel?

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희영
희영 2024-1-5
评论： Angelo Yeo 2024-1-11
Hello.
I am a beginner in matlab.
I got the code in psychtoolbox that can make rotating cylinder.
I remember getting help here last time, so I'm asking a new question about the problem I wasn't able to solve.
I should know the width and height of cylinder and dot size by pixel unit to calculate visual angle.
But I could not know what matlab code to do this, only found the matlab code that change vector to pixel or image to pixel.
So I want to calculate the width and height of below cylinder code and dot size by pixel unit.
If anyone knows anything about this, I would appreciate it if you could let me know.
Thank you for reading this.
Below is rotating cylinder code file. It is consist of two file.
# first code file
clear;
makeCyl = 1;
%% parameters
W = 153; %width
ndot = 900;
NumFrames = 86;
stepD = 400; % ie the half perimeter of the cylinder
cylR = stepD/pi; %guarantee the cylinder aprroaches with the same distance per 180 degree as the figure walks a step
%% cylinder
if makeCyl
backCol=0.9;
dotx = sin((rand(1,ndot)-0.5)*pi)* W/2; %dots are more concentrated on the two boundaries after ttransformed to sin, more natural than sqrt
dotc = ones(1, ndot);
angs = 2*pi* rand(1,ndot);
angpf = 2*pi/NumFrames; %angle per frame
Cylin = NaN(NumFrames*3,ndot); %keep it the same format as the mov file
dotC = cell(NumFrames,1);
for zz = 1:NumFrames
Cylin(zz*3-2,:) = dotx;
Cylin(zz*3-1,:) = cylR*cos(angs);
Cylin(zz*3,:) = cylR*sin(angs); % all dots are in the same depth so that it won'd contain perspective cue when drawn by moglDrawDots3D
angs = angs-angpf;
dotc = ones(1, ndot);
dotc(:, mod(angs,2*pi)<=pi) = backCol;
dotC{zz}= [1;1;1]*dotc;
end
save('Cylin_aaa','Cylin' ,'ndot');
end
# second code file
InitializeMatlabOpenGL;
load('Cylin_aaa.mat')
nFrames = 60;
fr = 1;
InitializeMatlabOpenGL; % open GL reset, moglDrawDots3D Required for function execution
%Screen('Preference', 'SkipSyncTests', 1);
Screen('Preference', 'SkipSyncTests', 1) % Skip sync test for testing
whichScreen = max(Screen('Screens'));
[w, screenRect] = Screen('OpenWindow', whichScreen,[0 0 0],[]); % small screen output
ScreenCenter = [screenRect(3)/2 screenRect(4)/2];
commandwindow;
while fr <= 86
thefr = fr;
while thefr > nFrames; thefr =thefr-nFrames; end
disp(thefr); % Check frame progress
this_xyz = Cylin(thefr*3-2:thefr*3,:);
Screen('DrawDots',w, this_xyz(1:2,:),[],[255 255 255],ScreenCenter, 0);
% moglDrawDots3D(w, this_xyz, 1, [1 1 1]); %
Screen('Flip',w);
%WaitSecs(0.05); % To see the dot move slowly
fr = fr +1;
end
sca;

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采纳的回答

Angelo Yeo
Angelo Yeo 2024-1-9
编辑：Angelo Yeo 2024-1-9
Ran in:
1. By default, each dot has a size of 1 pixel. See Psychtoolbox-3 - Screen(‘DrawDots’) for details. To quote:
“size” is the diameter of each dot in pixels (default is 1)
2. In Psychtoolbox, drawing unit of dots is pixels. For example, the script below will plot 2 dots at center and 10 pixels right to the center.
InitializeMatlabOpenGL; % open GL reset, moglDrawDots3D Required for function execution
Screen('Preference', 'SkipSyncTests', 1) % Skip sync test for testing
whichScreen = max(Screen('Screens'));
[w, screenRect] = Screen('OpenWindow', whichScreen,[0 0 0],[]); % small screen output
ScreenCenter = [screenRect(3)/2 screenRect(4)/2];
commandwindow;
myDots = ...
[0, 10;
0, 0];
Screen('DrawDots',w, myDots,5,[255 255 255],ScreenCenter, 0);
Screen('Flip', w);
KbStrokeWait
sca;
3. According to #2, the width and height of the cylinder can be calculated in pixel like below.
load('Cylin_aaa.mat');
temp = Cylin(1:2,:); x = temp(1,:); y = temp(2, :);
width = max(x) - min(x) % pixels
width = 152.9998
height = max(y) - min(y) % pixels
height = 254.6442

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