GDAL ReadAsArray() 尝试读取 ENVI 文件时仅返回 nan 值

Question

我正在尝试使用 GDAL 和 Python 将 ENVI 文件作为数组读取

图片信息如下：

Driver: ENVI/ENVI .hdr Labelled
Files: IMG-VV-ALPSRP248213250-P1.1__D_pwr_geo_sigma
     IMG-VV-ALPSRP248213250-P1.1__D_pwr_geo_sigma.hdr
Size is 1659, 2775
Coordinate System is:
PROJCS["UTM Zone 16, Northern Hemisphere",
    GEOGCS["WGS 84",
        DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        TOWGS84[0,0,0,0,0,0,0],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.0174532925199433,
        AUTHORITY["EPSG","9108"]],
    AUTHORITY["EPSG","4326"]],
PROJECTION["Transverse_Mercator"],
PARAMETER["latitude_of_origin",0],
PARAMETER["central_meridian",-87],
PARAMETER["scale_factor",0.9996],
PARAMETER["false_easting",500000],
PARAMETER["false_northing",0],
UNIT["Meter",1]]
Origin = (332125.000000000000000,2017650.000000000000000)
Pixel Size = (25.000000000000000,-25.000000000000000)
Image Structure Metadata:
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  (  332125.000, 2017650.000) ( 88d35'16.06"W, 18d14'29.96"N)
Lower Left  (  332125.000, 1948275.000) ( 88d34'55.98"W, 17d36'53.41"N)
Upper Right (  373600.000, 2017650.000) ( 88d11'44.12"W, 18d14'40.22"N)
Lower Right (  373600.000, 1948275.000) ( 88d11'29.00"W, 17d37' 3.30"N)
Center      (  352862.500, 1982962.500) ( 88d23'21.23"W, 17d55'47.10"N)
Band 1 Block=1659x1 Type=Float32, ColorInterp=Undefined

我的代码如下：

driver = gdal.GetDriverByName('ENVI')
driver.Register()

#Mind the suffix (It is an ENVI file)    
file = 'C:/img.1__A_pwr_geo_sigma

raster = gdal.Open(file,gdal.GA_ReadOnly)

raster_array = raster.ReadAsArray()

print raster_array

输出：

>>>array([[ nan, nan, nan, ..., nan, nan, nan], [ nan, nan, nan, ..., nan, nan, nan], [ nan, nan, nan, ..., nan, nan, nan], ..., [ nan, nan, nan, ..., nan, nan, nan], [ nan, nan, nan, ..., nan, nan, nan], [ nan, nan, nan, ..., nan, nan, nan]], dtype=float32)

数组中的所有值都是 NaN，虽然我知道图像中有浮点 32 位值（使用 ENVI 软件检查）

我在这里做错了什么？还是后缀有问题？

我也尝试使用 gdal_translate 将 ENVI 格式转换为 Geotiff，但 GeoTiff 也会生成相同的数组。

Answer 1

好消息，并非所有值都是 nan。 GDAL 驱动程序 (v.1.9.1) 运行良好，有效数据在依赖 GDAL 的软件（例如 QGIS）中可见。

nan 值用于表示 NoData。 （通常，大多数人对 NoData 使用一些有限的“虚拟”值，例如 1e+20）。

import numpy as np
from osgeo import gdal
fname = r'C:\path\to\envi_data\IMG-HH-ALPSRP136260330-H1.1__A_pwr_geo_sigma'
ds = gdal.Open(fname, gdal.GA_ReadOnly)
band = ds.GetRasterBand(1)
print band.GetNoDataValue()
# None ## normally this would have a finite value, e.g. 1e+20
ar = band.ReadAsArray()
print np.isnan(ar).all()
# False
print '%.1f%% masked' % (np.isnan(ar).sum() * 100.0 / ar.size)
# 43.0% masked

在 Python/NumPy 中表示缺失值的数组的最佳方法是使用 masked array：

mar = np.ma.masked_array(ar, np.isnan(ar))
print mar.min(), np.median(mar), mar.mean(), mar.std(), mar.max()
# 0.000715672 0.148093774915 0.0921848740388 0.0700106260235 5.0