Read coordinates on a txt file and plot them over an image.

Question

Gabriel 2017-1-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/319028-read-coordinates-on-a-txt-file-and-plot-them-over-an-image

评论： Stelios Fanourakis 2018-5-1

Dear all,

I made a program that reads some coordinates (x, y) of a text file and plot the points over a gray image. The problem is that the 'y' coordinates are inverted. This problem doesn't happen when I draw a regular plot (without reading from a file).

How can I fix this issue?

Thanks in advance,

3 个评论
显示 1更早的评论隐藏 1更早的评论

Gabriel 2017-1-4

在 MATLAB Online 中打开

It is quite simple, indeed:

[x, y] = textread('coordfile.txt', '%f , %f');
imshow(img, []), hold on;
plot(x, y, 'r*')

I tried to use "flipud" but it didn't solve the problem.

Image Analyst 2017-1-4

Gabriel, do you want your x axis to be at the top of your image, with rising y values going downward? Or do you want your x axis to be at the bottom of your image, with rising y values going upward? And do you like the way your image is displayed, or do you wish the top were at the bottom and vice versa?

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Stephen23 2017-1-4

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/319028-read-coordinates-on-a-txt-file-and-plot-them-over-an-image#answer_249365

编辑：Stephen23 2017-1-4

Images are referenced to the top left of the image (due to traditions related to the scanning of a CRT), so this is how all image handling programs work with them. MATLAB simply follows this standard.

People who are used to plotting data relative to an x-axis at the bottom of their plot might get a bit confused, but need to learn that images use a different standard.

A simple internet search shows many questions already dealing with this topic, e.g.:

https://www.mathworks.com/matlabcentral/answers/94170-how-can-i-reverse-the-y-axis-when-i-use-the-image-or-imagesc-function-to-display-an-image-in-matlab

and is also explained in the documentation for the relevant functions, e.g. imagesc:

"The high-level version of imagesc calls newplot before plotting and sets these axes properties: ... YDir to 'reverse'. Values along the y-axis increase from top to bottom."

4 个评论
显示 2更早的评论隐藏 2更早的评论

Guillaume 2017-1-4

在 MATLAB Online 中打开

plot(x, size(img, 1) - y, 'r*')

would solve the problem quickly

Stelios Fanourakis 2018-5-1

Hey I am doing something similar but I cannot take anything as a result. I use

filePatternu = fullfile(destinationFolder, '*.dcm'); allFiles = dir(filePatternu);

for k= 2: 1: length(allFiles) baseFileName = allFiles(k).name; % e.g. "1.png" fullFileName = fullfile(destinationFolder, baseFileName); I = dicomread(fullFileName); % img respresents input image. pause(2) [x, y] = textread('imgpositions.txt', '%f , %f'); figure imshow(I, [x y]) drawnow; end

Although, I get no error still I get no image

请先登录，再进行评论。