在GDAL中柵格數據直接參與各種計算的重要對象是Band

摘錄官方描述：

Raster Band

A raster band is represented in GDAL with the GDALRasterBand class. It represents a single raster band/channel/layer. It does not necessarily represent a whole image. For instance, a 24bit RGB image would normally be represented as a dataset with three bands, one for red, one for green and one for blue.

Gdal 中數據以Dataset為基礎，具體的柵格數據值被存儲在這個Dataset的Band對象之中，一個Dataset可以存儲多個Band對象。例如RGB色彩模型的圖象，在GDAL的數據模型中被認為是一個擁有3個波段（分別對應R\G\B）的Dataset。

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A raster band has the following properties:

• A width and height in pixels and lines. This is the same as that defined for the dataset, if this is a full resolution band.

  ?該值在C#中通過Band.XSize, Band.YSize獲取

• A datatype (GDALDataType). One of Byte, UInt16, Int16, UInt32, Int32, Float32, Float64, and the complex types CInt16, CInt32, CFloat32, and CFloat64.

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• A block size. This is a preferred (efficient) access chunk size. For tiled images this will be one tile. For scanline oriented images this will normally be one scanline.

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• A list of name/value pair metadata in the same format as the dataset, but of information that is potentially specific to this band.

  ?實際上是以String[]方式存儲的(這是C/C++程序員的習慣做法)，猜測該matadata即是Dataset中獲取的metadata內容一致，且不全面。

• An optional description string.

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• An optional single nodata pixel value (see also NODATA_VALUES metadata on the dataset for multi-band style nodata values).

  在C#中Nodata是對band而言的，理論上如果一個Dataset包含多個Band對象，這些Band對象的Nodata值是不能保證一致的。所以需要分別獲取。另外需要注意的一點是，在創建要寫入數據的Dataset時，為其Band指定Nodata需要考慮這個數據本身的有效值范圍和DataType，設置合適的值。?

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• An optional nodata mask band marking pixels as nodata or in some cases transparency as discussed in RFC 15: Band Masks.

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• An optional list of category names (effectively class names in a thematic image).

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• An optional minimum and maximum value.

  ?該值用于獲取Band中數據的最大最小統計值，不過測試了下偶爾會出現統計值不正確的情況，建議自己寫方法來處理。

• An optional offset and scale for transforming raster values into meaning full values (i.e. translate height to meters).

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• An optional raster unit name. For instance, this might indicate linear units for elevation data.

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• A color interpretation for the band. This is one of:

  • GCI_Undefined: the default, nothing is known.
  • GCI_GrayIndex: this is an independent gray-scale image
  • GCI_PaletteIndex: this raster acts as an index into a color table
  • GCI_RedBand: this raster is the red portion of an RGB or RGBA image
  • GCI_GreenBand: this raster is the green portion of an RGB or RGBA image
  • GCI_BlueBand: this raster is the blue portion of an RGB or RGBA image
  • GCI_AlphaBand: this raster is the alpha portion of an RGBA image
  • GCI_HueBand: this raster is the hue of an HLS image
  • GCI_SaturationBand: this raster is the saturation of an HLS image
  • GCI_LightnessBand: this raster is the hue of an HLS image
  • GCI_CyanBand: this band is the cyan portion of a CMY or CMYK image
  • GCI_MagentaBand: this band is the magenta portion of a CMY or CMYK image
  • GCI_YellowBand: this band is the yellow portion of a CMY or CMYK image
  • GCI_BlackBand: this band is the black portion of a CMYK image.

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• A color table, described in more detail later.

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• Knowledge of reduced resolution overviews (pyramids) if available.

其實在真正使用中，比較重要的無非是數據的nodata、xSize、ySize等等，投影等信息由Dataset獲取。用于應付一般情況下的簡單計算問題不大。

下一篇將詳細解釋一個常規的數據讀取和處理的流程。

轉載于:https://www.cnblogs.com/DannielZhang/p/5183761.html

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