maxPixels
该maxPixels参数旨在防止无意中创建非常大的导出。如果默认值对于您想要的输出图像来说太低，您可以增加maxPixels. 例如：
Export.image.toDrive({
image: landsat,
description: 'maxPixelsExample',
scale: 30,
region: geometry,
maxPixels: 1e9//改变这个参数可以让你的下载量成10倍百倍千倍的增加
});导出硬盘的函数：
Export.image.toDrive(image, description, folder, fileNamePrefix, dimensions, region, scale, crs, crsTransform, maxPixels, shardSize, fileDimensions, skipEmptyTiles, fileFormat, formatOptions)
Creates a batch task to export an Image as a raster to Drive. Tasks can be started from the Tasks tab. "crsTransform", "scale", and "dimensions" are mutually exclusive.
创建一个批处理任务，将图像作为栅格导出到驱动器。任务可以从 "任务 "选项卡开始。"crsTransform"、"scale "和 "dimensions "是相互排斥的。
Arguments:
image (Image):
The image to export.
description (String, optional):
A human-readable name of the task. May contain letters, numbers, -, _ (no spaces). Defaults to "myExportImageTask".
folder (String, optional):
The Google Drive Folder that the export will reside in. Note: (a) if the folder name exists at any level, the output is written to it, (b) if duplicate folder names exist, output is written to the most recently modified folder, (c) if the folder name does not exist, a new folder will be created at the root, and (d) folder names with separators (e.g. 'path/to/file') are interpreted as literal strings, not system paths. Defaults to Drive root.
fileNamePrefix (String, optional):
The filename prefix. May contain letters, numbers, -, _ (no spaces). Defaults to the description.
dimensions (Number|String, optional):
The dimensions to use for the exported image. Takes either a single positive integer as the maximum dimension or "WIDTHxHEIGHT" where WIDTH and HEIGHT are each positive integers.
region (Geometry.LinearRing|Geometry.Polygon|String, optional):
A LinearRing, Polygon, or coordinates representing region to export. These may be specified as the Geometry objects or coordinates serialized as a string. If not specified, the region defaults to the viewport at the time of invocation.
scale (Number, optional):
Resolution in meters per pixel. Defaults to 1000.
crs (String, optional):
CRS to use for the exported image.
crsTransform (List<Number>|String, optional):
Affine transform to use for the exported image. Requires "crs" to be defined.
maxPixels (Number, optional):
Restrict the number of pixels in the export. By default, you will see an error if the export exceeds 1e8 pixels. Setting this value explicitly allows one to raise or lower this limit.这里最大可以设置为1e13,
shardSize (Number, optional):
Size in pixels of the tiles in which this image will be computed. Defaults to 256.
fileDimensions (List<Number>|Number, optional):
The dimensions in pixels of each image file, if the image is too large to fit in a single file. May specify a single number to indicate a square shape, or an array of two dimensions to indicate (width,height). Note that the image will still be clipped to the overall image dimensions. Must be a multiple of shardSize.
skipEmptyTiles (Boolean, optional):
If true, skip writing empty (i.e. fully-masked) image tiles. Defaults to false.
fileFormat (String, optional):
The string file format to which the image is exported. Currently only 'GeoTIFF' and 'TFRecord' are supported, defaults to 'GeoTIFF'.
formatOptions (ImageExportFormatConfig, optional):
A dictionary of string keys to format specific options.
