How to 'Mirror Image' my Vectors

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Maskus Kit 2021-3-16

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评论： Bjorn Gustavsson 2021-3-17

Hello friends,

Been struggling with what might be a simple issue but can't seem to figure out. I have two vectors that are a 'mirror image' of themselves when plotted. Can anyone help me reorient them properly? I have tried flipud and fliplr but no success!

Attached the mirror image and the x and y vectors in spreadsheet. Any ideas will be deeply appreciated!

Thanks.

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Maskus Kit 2021-3-16

在 MATLAB Online 中打开

@Walter Roberson Thanks very much for your reply and insights. I'll try clarify my problem, and sorry for framing my question so poorly.

So the x and y vector values are actually pixel coordinates with corresponding z values for velocity (which I haven't attached). I have written a script (attached) that transforms these pixel coordinates to British National Grid coordinates following which I plot them in QGIS as per the attached image.

The 'problem' here is, when I plot these coordiantes in GIS (the image is attached is actually a screen grab from QGIS) the x and y coordinates are not in their correct location, they are clearly 'mirrored' for some reason. What I'm trying to do is get them in the right location - remove this 'mirror' effect.

Is there a way to resolve this? Thanks so much. Attached my transformation script (which does work and completes the transform, justwith the annoying 'mirroring'.

movingPointsM = [10.28,6.02;19.97,7.29;27.07,7.09;33.75,6.13;7.82,14.63;15.74,15.69;26.90,16.52;34.88,15.56]; %Co-ordinates from PIVlab   
% fixedPointsM = [29.8076,	24.5377;21.3091,	30.6566;9.5556,	15.9563;16.958,	24.0496;24.7148	,37.4257;22.1936,	14.7003;34.0778,	32.4643;15.9756,	8.3569];
% First fixedPointsM are subsampled GCP GPS data - second fixedPointsM are
% real-world coordinates, no edit - and can be used to plot the vels in the
% correct coordinate system. 
fixedPointsM = [351134.02,512791.64; 351127.80,512785.29;351120.19,512775.46;351115.92,512767.53;351140.44,512784.04;351133.04,512775.95;351128.69,512769.34;351127.28,512762.57]; % image px for specific video
mytform = fitgeotrans(movingPointsM, fixedPointsM, 'affine');% Reproject the data array so that it is consistent with metric spatial reference used for KLT-PIV
[x, y] = transformPointsForward(mytform, x(:), y(:)); %xdataOrig,ydataOrig
figure();
scatter(fixedPointsM(:,1), fixedPointsM(:,2));hold on; % Check that the GCP transformation works well
%scatter(x(:),y(:));
writematrix([x(:), y(:)],'transformed.txt', 'Delimiter', ',');

Walter Roberson 2021-3-16

To check the obvious: if you are using GIS, then are you making sure you use longitude -> x and latitude -> y, and that latitude corresponds to rows in MATLAB arrays and that longitude corresponds to columns in MATLAB arrays?

Maskus Kit 2021-3-16

@Walter Roberson Those are correct, the x (longitudes) and y (latitudes).

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采纳的回答

Bjorn Gustavsson 2021-3-16

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https://ww2.mathworks.cn/matlabcentral/answers/774242-how-to-mirror-image-my-vectors#answer_649147

mirror_point_line.m

If your yellow point-markers are supposed to lie on/in/over the stream (river?) then you might have to either rotate their coordinates around the centre of the scene, or perhaps mirror the coordinates on the diagonal. For the latter case I attach a function that mirror points relative to a line.

HTH

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Maskus Kit 2021-3-17

@Bjorn Gustavsson Works perfectly! Thanks :)

Bjorn Gustavsson 2021-3-17

My pleasure!

(Please share/upload the corrected points-overlayed-on-image figure - it would bring me(us?) joy...)

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