GDAL ReadAsArray未能忽略NoData值

Question

我正在尝试把一个TIFF文件的波段读取成一个数组。问题是GDAL没有忽略那些“无数据”的值。有没有办法让GDAL忽略这些值呢？

当我计算统计数据时，GDAL会忽略“无数据”的值。

import os, sys, gdal, ogr, numpy
from gdalconst import *

# register all of the drivers
gdal.AllRegister()

# open the image
ds = gdal.Open('test_slope.tif', GA_ReadOnly)

# get image size
rows = ds.RasterYSize
cols = ds.RasterXSize
bands = ds.RasterCount

# Set NoData Value
band = ds.GetRasterBand(1)
ndv = -3.4028230607371e+38
band.SetNoDataValue(ndv)

# Get Statistics
stats = band.ComputeStatistics(0)
print stats

# read in band as array
bandList = []
band.GetNoDataValue()
data = band.ReadAsArray(0, 0, cols, rows)
print data


>>> 
[0.0, 126.59918975830078, 25.757117870945123, 15.399812314100501]
[[ -3.40282306e+38  -3.40282306e+38  -3.40282306e+38 ...,  -3.40282306e+38
   -3.40282306e+38  -3.40282306e+38]
 [ -3.40282306e+38  -3.40282306e+38  -3.40282306e+38 ...,  -3.40282306e+38
   -3.40282306e+38  -3.40282306e+38]
 [ -3.40282306e+38  -3.40282306e+38  -3.40282306e+38 ...,  -3.40282306e+38
   -3.40282306e+38  -3.40282306e+38]
 ..., 
 [ -3.40282306e+38  -3.40282306e+38  -3.40282306e+38 ...,  -3.40282306e+38
   -3.40282306e+38  -3.40282306e+38]
 [ -3.40282306e+38  -3.40282306e+38  -3.40282306e+38 ...,  -3.40282306e+38
   -3.40282306e+38  -3.40282306e+38]
 [ -3.40282306e+38  -3.40282306e+38  -3.40282306e+38 ...,  -3.40282306e+38
   -3.40282306e+38  -3.40282306e+38]]
>>> 

Answer 1

我觉得你可以从你的 numpy.ndarray 创建一个 numpy.MaskedArray：

import numpy as np
import numpy.ma as ma

ndv = -3.40282306e+38

data = np.array([[0.0, 126.59918975830078, 25.757117870945123, 15.399812314100501],
                [-3.40282306e+38, -3.40282306e+38, -3.40282306e+38, -3.40282306e+38]])

masked_data = ma.masked_where(data == ndv, data)
print masked_data

结果：

[[0.0 126.599189758 25.7571178709 15.3998123141]
[-- -- -- --]]

在 numpy 中，结合使用 numpy.ndarray 和一个掩码，可以处理缺失的数据。