78 lines
2.5 KiB
Go
78 lines
2.5 KiB
Go
package raster
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import "context"
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// Grid describes a raster's pixel grid: its size, geotransform, and
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// projection. Two grids describe the same pixels when IO.SameGrid reports
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// true for them.
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type Grid struct {
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Width, Height int
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GeoTransform [6]float64
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ProjectionWKT string
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}
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// Window is a rectangular block of pixels within a raster, in pixel/line
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// coordinates with (0,0) at the top-left corner.
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type Window struct {
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X, Y, Width, Height int
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}
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// Reader reads pixel data and metadata from an existing raster.
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type Reader interface {
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// Grid returns the raster's pixel grid.
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Grid() Grid
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// NoData returns the raster's nodata value and whether one is set.
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NoData() (float64, bool)
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// ReadFloat64 reads the pixels in w into dst, row-major, converting the
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// underlying pixel type to float64. len(dst) must be at least
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// w.Width*w.Height.
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ReadFloat64(w Window, dst []float64) error
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// Close releases the underlying dataset handle.
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Close() error
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}
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// WriterOptions configures a raster created by IO.Create.
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type WriterOptions struct {
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// NoData is the nodata value written to the output band.
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NoData int16
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// TileSize is the internal tile size (both block dimensions) in pixels.
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TileSize int
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// Compression is the GDAL COMPRESS creation option value.
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Compression string
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}
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// Writer writes pixel data to a raster created by IO.Create.
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type Writer interface {
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// WriteInt16 writes src, row-major, into the pixels described by w.
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// len(src) must be at least w.Width*w.Height.
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WriteInt16(w Window, src []int16) error
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// Close flushes and releases the underlying dataset handle.
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Close() error
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}
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// IO is an engine-agnostic block I/O abstraction over raster storage. It lets
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// callers open and create rasters without depending on a particular GDAL
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// binding.
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type IO interface {
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// Open opens the raster at path for reading.
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Open(ctx context.Context, path string) (Reader, error)
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// Create creates a new single-band int16 raster at path with the given
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// grid and writer options, ready for WriteInt16 calls.
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Create(ctx context.Context, path string, g Grid, o WriterOptions) (Writer, error)
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// SameGrid reports whether a and b describe the same pixel grid: equal
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// size, geotransform, and coordinate reference system.
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SameGrid(a, b Grid) bool
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}
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// Windows tiles a w×h raster into row-major windows of at most size×size.
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func Windows(w, h, size int) []Window {
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var out []Window
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for y := 0; y < h; y += size {
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wh := min(size, h-y)
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for x := 0; x < w; x += size {
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out = append(out, Window{X: x, Y: y, Width: min(size, w-x), Height: wh})
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}
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}
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return out
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}
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