在Matlab中的pcolor中找到轮廓/边缘 [英] Find contour/edge in pcolor in Matlab

问题描述

我正在尝试在Matlab的pcolor图中绘制遵循像素"边缘的轮廓.这可能是图片中最好的解释.这是我的数据图.黄色数据(data == 1)和蓝色数据(data == 0)之间有明显的界限:

I'm trying to make a contour that follows the edges of the 'pixels' in a pcolor plot in Matlab. This is probably best explained in pictures. Here is a plot of my data. There is a distinct boundary between the yellow data (data==1) and the blue data (data==0):

请注意，这是一个pcolor图，因此每个正方形"本质上都是一个像素.我想返回遵循黄色数据 pixels 的 faces 的轮廓，不只是黄色数据的边缘.

Note that this is a pcolor plot so each 'square' is essentially a pixel. I want to return a contour that follows the faces of the yellow data pixels, not just the edge of the yellow data.

因此，输出轮廓(绿线)穿过像素的脸部(红点)的中点.

So the output contour (green line) passes through the mid-points of the face (red dots) of the pixels.

请注意，我不希望轮廓跟随数据的中心点(黑点)，这会像绿线一样.使用contour即可轻松实现.

Note that I don't want the contour to follow the centre points of the data (black dots), which would do something like this green line. This could be achieved easily with contour.

此外，如果有帮助，我会提供一些有用的网格.我在像素中间有个点(显然，这就是我在这里绘制的)，在角上也有点，在西/东面和北/南面上也有点.如果您熟悉荒川网格，则这是荒川C网格，所以我有rh-，u-，v-和psi-点.

Also, if it's any help, I have a few grids which may be useful. I have the points in the middle of the pixels (obviously, as that's what I've plotted here), I also have the points on the corners, AND I have the points on the west/east faces and the north/south faces. IF you're familiar with Arakawa grids, this is an Arakawa-C grid, so I have the rho-, u-, v- and psi- points.

我尝试了插值，网格交织以及其他一些功能，但是我没有任何运气.任何帮助将不胜感激，并将阻止我发疯.

I've tried interpolation, interweaving grids, and a few other things but I'm not having any luck. Any help would be HUGELY appreciated and would stop me going crazy.

干杯，戴夫

对不起，我简化了图像，使我想解释的内容更加明显，但这是我要分离的区域的较大图像(放大后):

Sorry, I simplified the images to make what I was trying to explain more obvious, but here is a larger (zoomed out) image of the region I'm trying to separate:

如您所见，它是一个复杂的轮廓，它向西南"方向前进，然后环绕并向东北"移动.这是我想通过黑点画出的红线:

As you can see, it's a complex outline which heads in a "southwest" direction before wrapping around and moving back "northeast". And here is the red line that I'd like to draw, through the black points:

推荐答案

您可以通过对解决方案I进行一些修改来解决此问题发布到相关问题.我在问题data的一部分中使用了示例图像蒙版的一部分.首先，您需要填充蒙版中的孔，您可以使用 图像处理工具箱中的imfill :

You can solve this with a couple of modifications to a solution I posted to a related question. I used a section of the sample image mask in the question for data. First, you will need to fill the holes in the mask, which you can do using imfill from the the Image Processing Toolbox:

x = 1:15;  % X coordinates for pixels
y = 1:17;  % Y coordinates for pixels
mask = imfill(data, 'holes');

接下来，应用我的其他答案中的方法来计算轮廓坐标的有序集合(位于像素角上):

Next, apply the method from my other answer to compute an ordered set of outline coordinates (positioned on the pixel corners):

% Create raw triangulation data:
[cx, cy] = meshgrid(x, y);
xTri = bsxfun(@plus, [0; 1; 1; 0], cx(mask).');
yTri = bsxfun(@plus, [0; 0; 1; 1], cy(mask).');
V = [xTri(:) yTri(:)];
F = reshape(bsxfun(@plus, [1; 2; 3; 1; 3; 4], 0:4:(4*nnz(mask)-4)), 3, []).';

% Trim triangulation data:
[V, ~, Vindex] = unique(V, 'rows');
V = V-0.5;
F = Vindex(F);

% Create triangulation and find free edge coordinates:
TR = triangulation(F, V);
freeEdges = freeBoundary(TR).';
xOutline = V(freeEdges(1, [1:end 1]), 1);  % Ordered edge x coordinates
yOutline = V(freeEdges(1, [1:end 1]), 2);  % Ordered edge y coordinates

最后，您可以在像素边缘的中心处获得所需的坐标，如下所示:

Finally, you can get the desired coordinates at the centers of the pixel edges like so:

ex = xOutline(1:(end-1))+diff(xOutline)./2;
ey = yOutline(1:(end-1))+diff(yOutline)./2;

这是显示结果的图:

imagesc(x, y, data);
axis equal
set(gca, 'XLim', [0.5 0.5+size(mask, 2)], 'YLim', [0.5 0.5+size(mask, 1)]);
hold on;
plot(ex([1:end 1]), ey([1:end 1]), 'r', 'LineWidth', 2);
plot(ex, ey, 'k.', 'LineWidth', 2);

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