matlab - 构建每行变量的矩阵时出现问题

Question

我正在尝试为我将在我的数据集上定义的多边形的 4 个点创建一个循环。我使用 lat、lon、dlat 和 dlon 来说明这些观点

lat = [35.314166 35.413909 35.533307 35.751982 35.3142 35.1607 35.0475 34.9878 34.9441];
lon = [-119.865953 -119.970299 -120.086757 -120.300046 -119.8659 -119.7068 -119.5583 -119.4711 -119.4029];

dlat = 0.524893450440127;
dlon = 0.73025079017917;

首先，我想创建一个循环来创建 4 个点并将它们保存为矩阵 b 的第一行，大小为 (4,4)

这是我需要的矩阵

b = [p11 p12 p13 p14 ;
     p21 p22 p23 p24 ;
     p31 p32 p33 p34 ;
     p41 p42 p43 p44]  

以下是我要定义的前两个多边形点的示例：

 p11 = [lon(9) + dlon, lat(9) + dlat]
 p12 = [lon(8) + dlon, lat(8) + dlat]
 p13 = [lon(8) - dlon, lat(8) - dlat]
 p14 = [lon(9) - dlon, lat(9) - dlat]

 p21 = [lon(8) + dlon, lat(8) + dlat]
 p22 = [lon(7) + dlon, lat(7) + dlat]
 p23 = [lon(7) - dlon, lat(7) - dlat]
 p24 = [lon(8) - dlon, lat(8) - dlat]

我一直在定义这个 for 循环，我什至不知道解决方案是否是 for 循环。请帮我。谢谢！

标签： matlabfor-loopmatrix

Answer 1

这里有两个解决方案。我试图尽可能接近您向我展示的非循环代码的一个：

s=numel(lon); % I guess we start at 9 because lon has 9 elements?
b=zeros(4,4,2);
for ix=1:size(b,1)
    %Calculate the indices of lon and lat
    index=s-ix;
    %very similar to the example you showed, insert the data into the
    %matrix
    b(ix,1,:)=[lon(index+1) + dlon, lat(index+1) + dlat];
    b(ix,2,:)=[lon(index)   + dlon, lat(index)   + dlat];
    b(ix,3,:)=[lon(index)   - dlon, lat(index)   - dlat];
    b(ix,4,:)=[lon(index+1) - dlon, lat(index+1) - dlat];
end

这里有一个替代方案，可以稍微减少代码。

s=numel(lon); % I guess we start at 9 because lon has 9 elements?
b=zeros(4,4,2);
for ix=1:size(b,1)
    %Calculate the indices of lon and lat
    index=s-ix+[1,0,0,1];
    %Build up one slice
    h=([lon(index);lat(index)]+[dlon;dlat].*[1,1,-1,-1]).';
    %insert h into the matrix. h is wrong way round, so it is transposed.
    b(ix,:,:)=h.';
end