Question

我正在处理一个我没写过的NDVI脚本，我正试图让它运行。它遇到的问题是旧的类型错误：无法隐式地将字节对象转换为str。直到昨天我才从未见过结构包，经过相当多的研究，我一般都理解这个概念，但并不完全具体。

我正在处理tiff文件并尝试创建NDVI图像。这是代码示例。如果有人能帮助我理解这一点并帮助我解决问题，我将非常感激！

## The function which loops through the input image and
## calculates the output NDVI value to be outputted.
def calcNDVI(self, filePath, outFilePath):

    # Open the inputted dataset
    dataset = gdal.Open(filePath, gdal.GA_ReadOnly)

    # Check the dataset successfully opened
    if dataset is None:
        print("The dataset could not be opened")
        sys.exit(-1)

    # Create the output dataset
    outDataset = self.createOutputImage(outFilePath, dataset)
    # Check the datasets successfully created
    if outDataset is None:
        print("Could not create output image")
        sys.exit(-1)

    # Get hold of the RED and NIR image bands from the image
    # Note that the image bands are hard coded to handle
    # landsat 8 TIFFs that produce separate images per band
    # which are mosaiced together where 
    # Red = band 1 and NIR = band 2
    red_band = dataset.GetRasterBand(1)
    nir_band = dataset.GetRasterBand(2)

    # Retrieve the number of lines within the image
    numLines = red_band.YSize

    # Loop through each line in turn:
    for line in range(numLines):
        # Define variable for output line
        outputLine = ''

        # Read in data for the current line from the
        # image band representing the red wavelength
        red_scanline = red_band.ReadRaster(0, line, red_band.XSize, 1, \
                red_band.XSize, 1, gdal.GDT_Float32)
        # Unpack the line of data to be read as floating point data
        red_tuple = struct.unpack('f' * red_band.XSize, red_scanline)

        # Read in data for the current line from the
        # image band representing the NIR wavelength
        nir_scanline = nir_band.ReadRaster(0, line, nir_band.XSize, 1, \
                nir_band.XSize, 1, gdal.GDT_Float32)
        # Unpack the line of data to be read as floating point data
        nir_tuple = struct.unpack('f' * nir_band.XSize, nir_scanline)

        # Loop through the columns within the image
        for i in range(len(red_tuple)):
            # Calculate the NDVI for the current pixel
            ndvi_lower = (nir_tuple[i] + red_tuple[i])
            ndvi_upper = (nir_tuple[i] - red_tuple[i])
            ndvi = 0
            # Be careful of zero divide
            if ndvi_lower == 0:
                ndvi = 0
            else:
                ndvi = ndvi_upper/ndvi_lower

            # Add the current pixel to the output line
            outputLine = outputLine + struct.pack('f', ndvi)

            # Write the completed line to the output image
            outDataset.GetRasterBand(1).WriteRaster(0, line, red_band.XSize, 1, \
            outputLine, buf_xsize=red_band.XSize, buf_ysize=1, buf_type = gdal.GDT_Float32)

            # Delete the output line following write
            del outputLine

运行时的输出：

outputLine = outputLine + struct.pack('f', ndvi)

TypeError: Can't convert 'bytes' object to str implicitly

再一次，非常感谢任何帮助！此外，本网站和其他地方有关于此特定结构错误的几个问题，但没有具体处理图像的任何问题。

谢谢！

Answer 1

好的我找到了答案，如果有人有类似的问题，这就熬夜了！导致错误的输出行：

outputLine = outputLine + struct.pack('f', ndvi)

可以通过一个非常简单的解决方案来解决：

outputLine = outputLine + str(struct.pack('f', ndvi))

Python无法隐式转换字节对象，但您可以明确地进行转换。

打包和解包GTiff文件的结构

1 个答案: