Fourier2d(SpatialVx)
Fourier2d()所属R语言包：SpatialVx
Function to compute the Fast Fourier Transform (FFT) of a gridded field.
函数来计算的网格领域的快速傅立叶变换（FFT）。
译者：生物统计家园网 机器人LoveR
描述----------Description----------
Function to compute the Fast Fourier Transform (FFT) of a gridded field. The field is first expanded, and zero padded.
函数来计算的网格领域的快速傅立叶变换（FFT）。该字段是第一扩大，零填充。
用法----------Usage----------
Fourier2d(x, bigdim = NULL, kdim = NULL)
参数----------Arguments----------
参数：x
n X m matrix giving the gridded field to transform.
N×M矩阵的格点场进行改造。
参数：bigdim
(optional) numeric vector of length 2. If NULL, it will be found from kdim. One of this argument or kdim must be given.
（可选）数字矢量长度为2。如果为NULL，它会被发现从kdim。其中一个这种说法或kdim的必须提供。
参数：kdim
(optional) numeric vector of length 2 giving the dimension of the kernel to be applied. If bigdim is NULL, then the optimal dimension for the FFT is calculated from teh dimension of x and kdim.
（可选）数值向量的长度为2的维度要应用的内核。如果bigdim是NULL，则最佳的FFT尺寸计算从德维度x和kdim。
Details
详细信息----------Details----------
The gridded field is expanded to bigdim, which is the nearest power of 2 above N=dim( x) + kdim - 1 if N <= 1024, or to the nearest multiple of 512 otherwise, if bigdim is not supplied. x is placed in the upper left corner of a matrix of zeros that has dimension bigdim. Missing values are replaced by zero. The FFT is conducted on the expanded/zero-padded gridded field. This is intended to be used more internally for the kernel2dsmooth function in order to reduce the number of FFT's that need be calculated (e.g., if performed for the same threshold over several neighborhood lengths). It is currently not used by SpatialVx function anymore, but may still be usefull.
网格领域扩展到bigdim，这是最近的2的幂以上N = DIM（X）+ kdim - 1，如果N <= 1024，或到最近的512的倍数，否则，如果不提供bigdim。 x被放置在左上角的一个矩阵，具有维度bigdim的零。缺少的值被替换为零。 FFT进行网格化领域的展开/零填充。这是为了更kernel2dsmooth函数内部使用，以减少的数量的需要来计算（例如，如果在几个分数：长度为相同的阈值进行）的FFT。这是目前所使用的SpatialVx的函数了，但仍可能是很有用的。
值----------Value----------
A possibly complex matrix of size bigdim of the Fourier transformed gridded field is returned.
一个可能的大小bigdim的傅里叶变换网格领域的复杂的矩阵将被返回。
（作者）----------Author(s)----------
Eric Gilleland
参见----------See Also----------
fft, kernel2dsmooth, hoods2d, kernel2dmeitsjer
fft，kernel2dsmooth，hoods2d，kernel2dmeitsjer
实例----------Examples----------
look <- matrix( 0, 10, 12)
look[4,7] <- 1
lookFFT <- Fourier2d( look, kdim=c(3,3))
# Now, call 'kernel2dsmooth' with a neighborhood boxcar kernel that averages the[现在，所谓的“kernel2dsmooth与附近棚车内核，平均的]
# nearest grid squares (i.e., neighborhood length of 3). That is, a square[最近的方格（即，邻里长度为3）。也就是说，一个正方形]
# of 1/(3^2) = 1/9 ~ 0.111111 with length 3 surrounding the 1 in 'look'.[1 /（3 ^ 2）= 1/9~0.111111周围长度为3 1“看”。]
kernel2dsmooth( look, kernel.type="boxcar", n=3, X=lookFFT)
# Note that the above could have been done with just:[注意，上面的本来可以做，只需：]
kernel2dsmooth( look, kernel.type="boxcar", n=3)
# But, in the previous one, one less FFT was calculated.[但是，在前面的一个，少了一个FFT计算。]
转载请注明:出自 生物统计家园网(http://www.biostatistic.net)。
注：
注1：为了方便大家学习，本文档为生物统计家园网机器人LoveR翻译而成，仅供个人R语言学习参考使用，生物统计家园保留版权。
注2：由于是机器人自动翻译，难免有不准确之处，使用时仔细对照中、英文内容进行反复理解，可以帮助R语言的学习。
注3：如遇到不准确之处，请在本贴的后面进行回帖，我们会逐渐进行修订。
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发表于 2012-9-30 12:55:22
