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

1 次查看（过去 30 天）
Gabriel
Gabriel 2017-1-4
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
Gabriel
Gabriel 2017-1-4
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
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。

回答（1 个）

Stephen23
Stephen23 2017-1-4
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
Stelios Fanourakis
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。

类别

在 Help Center 和 File Exchange 中查找有关 Annotations 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by