baselineCorrection(TargetSearch)
baselineCorrection()所属R语言包：TargetSearch
Baseline correction algorithm
基线校正算法
译者：生物统计家园网 机器人LoveR
描述----------Description----------
Functions for baseline correction of GC-MS chromatograms.
GC-MS分析色谱基线校正功能。
用法----------Usage----------
baselineCorrection(int, threshold = 0.5, alpha = 0.95, bfraction = 0.2,
segments = 100, signalWindow = 10, method = "linear")
baseline(ncData, baseline.opts = NULL)
参数----------Arguments----------
参数：int
A matrix object of spectra peak intensities to be baseline corrected, where the columns are retention times and rows mass traces.
矩阵的谱峰强度的对象是基线校正，其中列保留时间和行大规模的痕迹。
参数：threshold
A numeric value between 0 and 1. A value of one sets the baseline above the noise, 0.5 in the middle of the noise and 0 below the noise.
0和1之间的一个数值。一个一个的值设置基线以上的噪音，在中间的噪音和噪音低于0.5。
参数：alpha
The alpha parameter of the high pass filter.
高通滤波器的alpha参数。
参数：bfraction
The percentage of the fragments with the lowest intensities of the filtered signal that are assumed to be baseline signal.
比例最低的假设为基准信号的滤波信号强度的片段。
参数：segments
The number of segments in which the filtered signal is divided.
过滤信号分为数段。
参数：signalWindow
The window size (number of points) used in the signal windowing step.
信号窗口步骤中使用的窗口大小（点数）。
参数：method
The method used to approximate the baseline. "linear" (default) uses linear interpolation. "spline" fits a cubic smoothing spline (warning: really slow).
所采用的方法近似基线。 "linear"（默认），采用线性插值。 "spline"适合三次样条（警告：真的很慢）。
参数：ncData
A list returned by the function xcms:::netCDFRawData </table>
返回一个列表功能xcms:::netCDFRawData</ TABLE>
参数：baseline.opts
A list with parameters to be passed to baselineCorrection function. For example baseline.opts = list(threshold = 0.5, alpha = 0.95).
要传递给baselineCorrection函数与参数列表。例如baseline.opts = list(threshold = 0.5, alpha = 0.95)。
Details
详情----------Details----------
The baseline correction algorithm is based on the work of Chang et al, and it works as follows. For every mass trace, i.e., rows of matrix int, the signal intensity is filtered by a first high pass filter: y[i] = alpha * (y[i-1] + x[i] - x[i-1]). The filtered signal is divided into evenly spaced segments (segments) and the standard deviation of each segment is calculated. A percentage (bfraction) of the segments with the lowest values are assumed to be baseline signal and the standard deviation (stdn) of the points within those segments is calculated.
基线校正算法是基于对Chang等人的工作，它的工作原理如下。对于每一个质量跟踪，即行矩阵int第一个高通滤波器滤波，信号强度：Y [I] =阿尔法*（Y [I-1] + X [I] - X [ I-1]）。滤波后的信号分为均匀分布段（segments）和各分部的标准偏差的计算。一个最低值段的百分比（bfraction）被假定为基准信号，并在这些细分点（stdn）的标准差计算。
Once stdn has been determined, the points with absolute filtered values larger than 2 * stdn are considered signal. After that, the signal windowing step takes every one of the points found to be signal as the center of a signal window (signalWindow) and marks the points within that window as signal. The remaining points are now considered to be noise.
一旦stdn已经确定，绝对过滤值大于2点* stdn被视为信号。之后，信号窗口的步骤，每一个发现是一个信号窗口中心（signalWindow)“商标，由于信号的窗口内点信号点。其余点现在被认为是噪音。
The baseline signal is obtained by either using linear interpolation (default) or fitting a cubic smoothing spline taking only the noise. The baseline can be shifted up or down by using the parameter (threshold), which is done by the formula: B' = B + 2*(threshold - 0.5)*2*stdn, where B is the fitted spline, stdn the standard deviation of the noise, and threshold a value between 0 and 1. Finally, the corrected signal is calculated by subtracting B' to the original signal.
基准信号获得通过使用线性插值（默认）或装修三次样条，只有噪音。基线可以转移或使用参数（阈值），由公式：B“的B + 2 *（阈值 - 0.5）* 2 * stdn，其中B是装样条，stdn标准噪音，threshold0和1之间的值的偏差。最后计算减去B的原始信号，纠正信号。
The baseline function is called by the function NetCDFPeakFinding before the peak picking algorithm is performed. Since it is an internal function, it is not intended to be executed directly.
baseline函数被调用由NetCDFPeakFinding前峰值采摘算法执行的功能。因为它是一个内部函数，它不打算直接执行。
值----------Value----------
A matrix of the same dimensions of int with the baseline corrected intensities.
int基线校正强度的尺寸相同的矩阵。
作者（S）----------Author(s)----------
Alvaro Cuadros-Inostroza
参考文献----------References----------
for signal dense NMR spectra. Journal of Magnetic Resonance 187 (2007) 288-292
参见----------See Also----------
RIcorrect
RIcorrect
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。
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发表于 2012-2-26 15:22:00
