Extracting the indices in a 2D map associted with lines drawn over the map

1 次查看（过去 30 天）

Sai Prasanth 2021-5-20

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/835628-extracting-the-indices-in-a-2d-map-associted-with-lines-drawn-over-the-map

评论： Sai Prasanth 2021-6-11

Hello,

I have a 2D map of some geophysical variable. Visually, to mark the regions of interest and draw cross-sections, I have drawn several lines that indicate the various regions of the map. Now, I would like to extract the indices associated with each of these lines. I would then like to average the geophysical variable once I know the indices (which is simple). I just don't know how to extract the indices given these lines.

Any guidance will be appreciated!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Image Analyst 2021-5-20

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/835628-extracting-the-indices-in-a-2d-map-associted-with-lines-drawn-over-the-map#answer_704918

Use improfile() to draw your lines. Two of the outputs will be the vector of x and vector of y values for the line you drew.

10 个评论
显示 8更早的评论隐藏 8更早的评论

Image Analyst 2021-6-4

在 MATLAB Online 中打开

I don't understand what you're saying. Maybe if you say this before you draw:

axis('on', 'image');

you'll see that the cx and cy DO have coordinate values that correspond to the actual pixel location in the image. If you have some other calibration system, then you'll have to convert the pixel locations from a digital image into something else, like latitude or longitude or kilometers or whatever. To convert to kilometers - that's trivial. To get latitude and longitude, there might be something in the Mapping Toolbox that might help (I don't have it).

So getting back to your question: "The whole point of drawing these lines was to be able to pick the array indices so that I could access the values at those specific locations to draw a histogram/average etc." I believe the cx and cy are the indices. Of course they're fractional because the profile is along a straight line. If you wanted integer coordinates to line up with rows and columns, then you can simply cast to integer by rounding:

cx = round(cx); % Round to nearest integer.
cy = round(cy); % Round to nearest integer.

Now the line will be jaggy. If you want to get the intensity along the jaggy line, simply run along the line

for k = 1 : length(cx)
    intensity(k) = grayImage(cy(k), cx(k)); % Make sure y comes first, NOT x!
end

Sai Prasanth 2021-6-5

在 MATLAB Online 中打开

I guess, my problem would instantly be solved if there was a way to extract these indices from a line drawn on a plot - without the need for converting it to an image. Since improfile only works on images, the indices of an image are totally different.

Please see in the below code that creates a line on a simple pcolor plot - I would just like to know the indices that it passes through (without converting to an image).

f3 = figure('DefaultAxesFontSize',18, 'DefaultAxesTitleFontWeight','bold')
 set(gcf,'color','w');
 set(0,'DefaultAxesFontName','Times New Roman','DefaultTextFontName','Times New Roman','DefaultAxesFontWeight', 'bold'); 
 pcolor(wrfvars_time1.XLONG,wrfvars_time1.XLAT,log10(Int_icepath))
 xlabel('Longitude') 
 ylabel('Latitude') 
 title('log_{10}(Vertically Integrated Ice-Water) in g/m^2') 
 shading flat
 caxis([-2 5])
 xlim([-36 -25])
 ylim([6 16.15])
 colormap(map)
 colorbar; 
   
x1 = -34.49; 
x2 = -31.58; 
y1 = 11.01;
y2 = 11.67;  
plot([x1 x2], [y1 y2],'LineWidth',3,'Color','red');

Sai Prasanth 2021-6-11

@Image Analyst : Hi, can you please help me out with this one? I'd like to extract the indices from a line without going through an image.

请先登录，再进行评论。

请先登录，再回答此问题。

类别

MATLAB Graphics 2-D and 3-D Plots Surfaces, Volumes, and Polygons Surface and Mesh Plots

在 Help Center 和 File Exchange 中查找有关 Surface and Mesh Plots 的更多信息

产品

版本

R2019b

Community Treasure Hunt

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

Start Hunting!

Translated by

Extracting the indices in a 2D map associted with lines drawn over the map

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

回答（1 个）

10 个评论
显示 8更早的评论隐藏 8更早的评论

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

Extracting the indices in a 2D map associted with lines drawn over the map

0 个评论 显示 -2更早的评论隐藏 -2更早的评论

回答（1 个）

10 个评论 显示 8更早的评论隐藏 8更早的评论

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

10 个评论
显示 8更早的评论隐藏 8更早的评论