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Public Member Functions | List of all members
GDALMDArray Class Referenceabstract

Class modeling a multi-dimensional array. More...

`#include <gdal_priv.h>`

Inheritance diagram for GDALMDArray:

## Public Member Functions
GUInt64 | GetTotalCopyCost () const
| Return a total "cost" to copy the array. More...
virtual bool | CopyFrom (GDALDataset *poSrcDS, const GDALMDArray *poSrcArray, bool bStrict, GUInt64 &nCurCost, const GUInt64 nTotalCost, GDALProgressFunc pfnProgress, void *pProgressData)
| Copy the content of an array into a new (generally empty) array. More...
virtual bool | IsWritable () const =0
| Return whether an array is writable;.
virtual CSLConstList | GetStructuralInfo () const
| Return structural information on the array. More...
virtual const std::string & | GetUnit () const
| Return the array unit. More...
virtual bool | SetUnit (const std::string &osUnit)
| Set the variable unit. More...
virtual bool | SetSpatialRef (const OGRSpatialReference *poSRS)
| Assign a spatial reference system object to the the array. More...
virtual std::shared_ptr< OGRSpatialReference > | GetSpatialRef () const
| Return the spatial reference system object associated with the array. More...
virtual const void * | GetRawNoDataValue () const
| Return the nodata value as a "raw" value. More...
double | GetNoDataValueAsDouble (bool *pbHasNoData=nullptr) const
| Return the nodata value as a double. More...
virtual bool | SetRawNoDataValue (const void *pRawNoData)
| Set the nodata value as a "raw" value. More...
bool | SetNoDataValue (double dfNoData)
| Set the nodata value as a double. More...
virtual double | GetOffset (bool *pbHasOffset=nullptr) const
| Get the offset value to apply to raw values. More...
virtual double | GetScale (bool *pbHasScale=nullptr) const
| Get the scale value to apply to raw values. More...
virtual bool | SetOffset (double dfOffset)
| Set the offset value to apply to raw values. More...
virtual bool | SetScale (double dfScale)
| Set the scale value to apply to raw values. More...
std::shared_ptr< GDALMDArray > | GetView (const std::string &viewExpr) const
| Return a view of the array using slicing or field access. More...
std::shared_ptr< GDALMDArray > | operator[] (const std::string &fieldName) const
| Return a view of the array using field access. More...
template<typename... GUInt64VarArg>
std::shared_ptr< GDALMDArray > | at (GUInt64 idx, GUInt64VarArg...tail) const
| Return a view of the array using integer indexing. More...
virtual std::shared_ptr< GDALMDArray > | Transpose (const std::vector< int > &anMapNewAxisToOldAxis) const
| Return a view of the array whose axis have been reordered. More...
std::shared_ptr< GDALMDArray > | GetUnscaled () const
| Return an array that is the unscaled version of the current one. More...
virtual std::shared_ptr< GDALMDArray > | GetMask (CSLConstList papszOptions) const
| Return an array that is a mask for the current array. More...
virtual GDALDataset * | AsClassicDataset (size_t iXDim, size_t iYDim) const
| Return a view of this array as a "classic" GDALDataset (ie 2D) More...
Public Member Functions inherited from GDALAbstractMDArray
const std::string & | GetName () const
| Return the name of an array or attribute. More...
const std::string & | GetFullName () const
| Return the name of an array or attribute. More...
GUInt64 | GetTotalElementsCount () const
| Return the total number of values in the array. More...
virtual size_t | GetDimensionCount () const
| Return the number of dimensions. More...
virtual const std::vector< std::shared_ptr< GDALDimension > > & | GetDimensions () const =0
| Return the dimensions of an attribute/array. More...
virtual const GDALExtendedDataType & | GetDataType () const =0
| Return the data type of an attribute/array. More...
virtual std::vector< GUInt64 > | GetBlockSize () const
| Return the "natural" block size of the array along all dimensions. More...
virtual std::vector< size_t > | GetProcessingChunkSize (size_t nMaxChunkMemory) const
| Return an optimal chunk size for read/write oerations, given the natural block size and memory constraints specified. More...
virtual bool | ProcessPerChunk (const GUInt64 *arrayStartIdx, const GUInt64 *count, const size_t *chunkSize, FuncProcessPerChunkType pfnFunc, void *pUserData)
| Call a user-provided function to operate on an array chunk by chunk. More...
bool | Read (const GUInt64 *arrayStartIdx, const size_t *count, const GInt64 *arrayStep, const GPtrDiff_t *bufferStride, const GDALExtendedDataType &bufferDataType, void *pDstBuffer, const void *pDstBufferAllocStart=nullptr, size_t nDstBufferAllocSize=0) const
| Read part or totality of a multidimensional array or attribute. More...
bool | Write (const GUInt64 *arrayStartIdx, const size_t *count, const GInt64 *arrayStep, const GPtrDiff_t *bufferStride, const GDALExtendedDataType &bufferDataType, const void *pSrcBuffer, const void *pSrcBufferAllocStart=nullptr, size_t nSrcBufferAllocSize=0)
| Write part or totality of a multidimensional array or attribute. More...
Public Member Functions inherited from GDALIHasAttribute
virtual std::shared_ptr< GDALAttribute > | GetAttribute (const std::string &osName) const
| Return an attribute by its name. More...
virtual std::vector< std::shared_ptr< GDALAttribute > > | GetAttributes (CSLConstList papszOptions=nullptr) const
| Return the list of attributes contained in a GDALMDArray or GDALGroup. More...
virtual std::shared_ptr< GDALAttribute > | CreateAttribute (const std::string &osName, const std::vector< GUInt64 > &anDimensions, const GDALExtendedDataType &oDataType, CSLConstList papszOptions=nullptr)
| Create an attribute within a GDALMDArray or GDALGroup. More...

## Additional Inherited Members
Public Types inherited from GDALAbstractMDArray
typedef bool(* | FuncProcessPerChunkType) (GDALAbstractMDArray *array, const GUInt64 *chunkArrayStartIdx, const size_t *chunkCount, GUInt64 iCurChunk, GUInt64 nChunkCount, void *pUserData)
| Type of pfnFunc argument of ProcessPerChunk(). More...
Protected Member Functions inherited from GDALIHasAttribute
std::shared_ptr< GDALAttribute > | GetAttributeFromAttributes (const std::string &osName) const
| Possible fallback implementation for GetAttribute() using GetAttributes().

## Detailed Description

Class modeling a multi-dimensional array.

It has a name, values organized as an array and a list of GDALAttribute.

This is based on the HDF5 dataset concept

Since
  GDAL 3.1

## Member Function Documentation

GDALDataset * GDALMDArray::AsClassicDataset | ( | size_t | iXDim,
|  | size_t | iYDim
| ) |  | const
| virtual

Return a view of this array as a "classic" GDALDataset (ie 2D)

In the case of > 2D arrays, additional dimensions will be represented as raster bands.

The "reverse" method is GDALRasterBand::AsMDArray().

This is the same as the C function GDALMDArrayAsClassicDataset().

Parameters

  iXDim | Index of the dimension that will be used as the X/width axis.
  iYDim | Index of the dimension that will be used as the Y/height axis. Ignored if the dimension count is 1.

Returns
  a new GDALDataset that must be freed with GDALClose(), or nullptr

template<typename... GUInt64VarArg>

std::shared_ptr<GDALMDArray> GDALMDArray::at | ( | GUInt64 | idx,
|  | GUInt64VarArg... | tail
| ) |  | const
| inline

Return a view of the array using integer indexing.

Equivalent of GetView("[indices_0,indices_1,.....,indices_last]")

Example:

ar->at(0,3,2)

bool GDALMDArray::CopyFrom | ( | GDALDataset * | poSrcDS,
|  | const GDALMDArray * | poSrcArray,
|  | bool | bStrict,
|  | GUInt64 & | nCurCost,
|  | const GUInt64 | nTotalCost,
|  | GDALProgressFunc | pfnProgress,
|  | void * | pProgressData
| ) |  |
| virtual

Copy the content of an array into a new (generally empty) array.

Parameters

  poSrcDS | Source dataset. Migt be nullptr (but for correct behaviour of some output drivers this is not recommended)
  poSrcArray | Source array. Should NOT be nullptr.
  bStrict | Whether to enable stict mode. In strict mode, any error will stop the copy. In relaxed mode, the copy will be attempted to be pursued.
  nCurCost | Should be provided as a variable initially set to 0.
  nTotalCost | Total cost from GetTotalCopyCost().
  pfnProgress | Progress callback, or nullptr.
  pProgressData | Progress user data, or nulptr.

Returns
  true in case of success (or partial success if bStrict == false).

std::shared_ptr< GDALMDArray > GDALMDArray::GetMask | ( | CSLConstList | papszOptions | ) | const
| virtual

Return an array that is a mask for the current array.

This array will be of type Byte, with values set to 0 to indicate invalid pixels of the current array, and values set to 1 to indicate valid pixels.

The generic implementation honours the NoDataValue, as well as various netCDF CF attributes: missing_value, _FillValue, valid_min, valid_max and valid_range.

This is the same as the C function GDALMDArrayGetMask().

Parameters

  papszOptions | NULL-terminated list of options, or NULL.

Returns
  a new array, that holds a reference to the original one, and thus is a view of it (not a copy), or nullptr in case of error.

double GDALMDArray::GetNoDataValueAsDouble | ( | bool * | pbHasNoData = `nullptr` | ) | const

Return the nodata value as a double.

The value returned might be nullptr in case of no nodata value. When a nodata value is registered, a non-nullptr will be returned whose size in bytes is GetDataType().GetSize().

This is the same as the C function GDALMDArrayGetNoDataValueAsDouble().

Parameters

  pbHasNoData | Pointer to a output boolean that will be set to true if a nodata value exists and can be converted to double. Might be nullptr.

Returns
  the nodata value as a double. A 0.0 value might also indicate the absence of a nodata value or an error in the conversion (*pbHasNoData will be set to false then).

double GDALMDArray::GetOffset | ( | bool * | pbHasOffset = `nullptr` | ) | const
| virtual

Get the offset value to apply to raw values.

unscaled_value = raw_value * GetScale() + GetOffset()

This is the same as the C function GDALMDArrayGetOffset().

Note
  Driver implementation: this method shall be implemented if gettings offset is supported.

Parameters

  pbHasOffset | Pointer to a output boolean that will be set to true if a offset value exists. Might be nullptr.

Returns
  the offset value. A 0.0 value might also indicate the absence of a offset value.

const void * GDALMDArray::GetRawNoDataValue | ( |  | ) | const
| virtual

Return the nodata value as a "raw" value.

The value returned might be nullptr in case of no nodata value. When a nodata value is registered, a non-nullptr will be returned whose size in bytes is GetDataType().GetSize().

The returned value should not be modified or freed. It is valid until the array is destroyed, or the next call to GetRawNoDataValue() or SetRawNoDataValue(), or any similar methods.

Note
  Driver implementation: this method shall be implemented if nodata is supported.

This is the same as the C function GDALMDArrayGetRawNoDataValue().

Returns
  nullptr or a pointer to GetDataType().GetSize() bytes.

double GDALMDArray::GetScale | ( | bool * | pbHasScale = `nullptr` | ) | const
| virtual

Get the scale value to apply to raw values.

unscaled_value = raw_value * GetScale() + GetOffset()

This is the same as the C function GDALMDArrayGetScale().

Note
  Driver implementation: this method shall be implemented if gettings scale is supported.

Parameters

  pbHasScale | Pointer to a output boolean that will be set to true if a scale value exists. Might be nullptr.

Returns
  the scale value. A 1.0 value might also indicate the absence of a scale value.

std::shared_ptr< OGRSpatialReference > GDALMDArray::GetSpatialRef | ( |  | ) | const
| virtual

Return the spatial reference system object associated with the array.

This is the same as the C function GDALMDArrayGetSpatialRef().

CSLConstList GDALMDArray::GetStructuralInfo | ( |  | ) | const
| virtual

Return structural information on the array.

This may be the compression, etc..

The return value should not be freed and is valid until GDALMDArray is released or this function called again.

This is the same as the C function GDALMDArrayGetStruturalInfo().

GUInt64 GDALMDArray::GetTotalCopyCost | ( |  | ) | const

Return a total "cost" to copy the array.

Used as a parameter for CopyFrom()

const std::string & GDALMDArray::GetUnit | ( |  | ) | const
| virtual

Return the array unit.

Values should conform as much as possible with those allowed by the NetCDF CF conventions: http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/cf-conventions.html#units but others might be returned.

Few examples are "meter", "degrees", "second", ... Empty value means unknown.

This is the same as the C function GDALMDArrayGetUnit()

std::shared_ptr< GDALMDArray > GDALMDArray::GetUnscaled | ( |  | ) | const

Return an array that is the unscaled version of the current one.

That is each value of the unscaled array will be unscaled_value = raw_value * GetScale() + GetOffset()

This is the same as the C function GDALMDArrayGetUnscaled().

Returns
  a new array, that holds a reference to the original one, and thus is a view of it (not a copy), or nullptr in case of error.

std::shared_ptr< GDALMDArray > GDALMDArray::GetView | ( | const std::string & | viewExpr | ) | const

Return a view of the array using slicing or field access.

The slice expression uses the same syntax as NumPy basic slicing and indexing. See https://www.numpy.org/devdocs/reference/arrays.indexing.html#basic-slicing-and-indexing Or it can use field access by name. See https://www.numpy.org/devdocs/reference/arrays.indexing.html#field-access

Multiple [] bracket elements can be concatenated, with a slice expression or field name inside each.

For basic slicing and indexing, inside each [] bracket element, a list of indexes that apply to successive source dimensions, can be specified, using integer indexing (e.g. 1), range indexing (start:stop:step), ellipsis (...) or newaxis, using a comma separator.

Examples with a 2-dimensional array whose content is [[0,1,2,3],[4,5,6,7]].

- GetView("[1][2]"): returns a 0-dimensional/scalar array with the value at index 1 in the first dimension, and index 2 in the second dimension from the source array. That is 5
- GetView("[1]")->GetView("[2]"): same as above. Above is actually implemented internally doing this intermediate slicing approach.
- GetView("[1,2]"): same as above, but a bit more performant.
- GetView("[1]"): returns a 1-dimensional array, sliced at index 1 in the first dimension. That is [4,5,6,7].
- GetView("[:,2]"): returns a 1-dimensional array, sliced at index 2 in the second dimension. That is [2,6].
- GetView("[:,2:3:]"): returns a 2-dimensional array, sliced at index 2 in the second dimension. That is [[2],[6]].
- GetView("[::,2]"): Same as above.
- GetView("[...,2]"): same as above, in that case, since the ellipsis only expands to one dimension here.
- GetView("[:,::2]"): returns a 2-dimensional array, with even-indexed elements of the second dimension. That is [[0,2],[4,6]].
- GetView("[:,1::2]"): returns a 2-dimensional array, with odd-indexed elements of the second dimension. That is [[1,3],[5,7]].
- GetView("[:,1:3:]"): returns a 2-dimensional array, with elements of the second dimension with index in the range [1,3[. That is [[1,2],[5,6]].
- GetView("[::-1,:]"): returns a 2-dimensional array, with the values in first dimension reversed. That is [[4,5,6,7],[0,1,2,3]].
- GetView("[newaxis,...]"): returns a 3-dimensional array, with an addditional dimension of size 1 put at the beginning. That is [[[0,1,2,3],[4,5,6,7]]].

One difference with NumPy behaviour is that ranges that would result in zero elements are not allowed (dimensions of size 0 not being allowed in the GDAL multidimensional model).

For field access, the syntax to use is ["field_name"] or ['field_name']. Multipe field specification is not supported currently.

Both type of access can be combined, e.g. GetView("[1]['field_name']")

Note
  When using the GDAL Python bindings, natural Python syntax can be used. That is ar[0,::,1]["foo"] will be internally translated to ar.GetView("[0,::,1]['foo']")
  When using the C++ API and integer indexing only, you may use the at(idx0, idx1, ...) method.

The returned array holds a reference to the original one, and thus is a view of it (not a copy). If the content of the original array changes, the content of the view array too. When using basic slicing and indexing, the view can be written if the underlying array is writable.

This is the same as the C function GDALMDArrayGetView()

Parameters

  viewExpr | Expression expressing basic slicing and indexing, or field access.

Returns
  a new array, that holds a reference to the original one, and thus is a view of it (not a copy), or nullptr in case of error.

std::shared_ptr< GDALMDArray > GDALMDArray::operator[] | ( | const std::string & | fieldName | ) | const

Return a view of the array using field access.

Equivalent of GetView("['fieldName']")

Note
  When operationg on a shared_ptr, use (*array)["fieldName"] syntax.

bool GDALMDArray::SetNoDataValue | ( | double | dfNoData | ) |

Set the nodata value as a double.

If the natural data type of the attribute/array is not double, type conversion will occur to the type returned by GetDataType().

This is the same as the C function GDALMDArraySetNoDataValueAsDouble().

Returns
  true in case of success.

bool GDALMDArray::SetOffset | ( | double | dfOffset | ) |
| virtual

Set the offset value to apply to raw values.

unscaled_value = raw_value * GetScale() + GetOffset()

This is the same as the C function GDALMDArraySetOffset().

Note
  Driver implementation: this method shall be implemented if setting offset is supported.

Returns
  true in case of success.

bool GDALMDArray::SetRawNoDataValue | ( | const void * | pRawNoData | ) |
| virtual

Set the nodata value as a "raw" value.

The value passed might be nullptr in case of no nodata value. When a nodata value is registered, a non-nullptr whose size in bytes is GetDataType().GetSize() must be passed.

This is the same as the C function GDALMDArraySetRawNoDataValue().

Note
  Driver implementation: this method shall be implemented if setting nodata is supported.

Returns
  true in case of success.

bool GDALMDArray::SetScale | ( | double | dfScale | ) |
| virtual

Set the scale value to apply to raw values.

unscaled_value = raw_value * GetScale() + GetOffset()

This is the same as the C function GDALMDArraySetScale().

Note
  Driver implementation: this method shall be implemented if setting scale is supported.

Returns
  true in case of success.

bool GDALMDArray::SetSpatialRef | ( | const OGRSpatialReference * | poSRS | ) |
| virtual

Assign a spatial reference system object to the the array.

This is the same as the C function GDALMDArraySetSpatialRef().

bool GDALMDArray::SetUnit | ( | const std::string & | osUnit | ) |
| virtual

Set the variable unit.

Values should conform as much as possible with those allowed by the NetCDF CF conventions: http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/cf-conventions.html#units but others might be returned.

Few examples are "meter", "degrees", "second", ... Empty value means unknown.

This is the same as the C function GDALMDArraySetUnit()

Note
  Driver implementation: optionally implemented.

Parameters

  osUnit | unit name.

Returns
  true in case of success.

std::shared_ptr< GDALMDArray > GDALMDArray::Transpose | ( | const std::vector< int > & | anMapNewAxisToOldAxis | ) | const
| virtual

Return a view of the array whose axis have been reordered.

The anMapNewAxisToOldAxis parameter should contain all the values between 0 and GetDimensionCount() - 1, and each only once. -1 can be used as a special index value to ask for the insertion of a new axis of size 1. The new array will have anMapNewAxisToOldAxis.size() axis, and if i is the index of one of its dimension, it corresponds to the axis of index anMapNewAxisToOldAxis[i] from the current array.

This is similar to the numpy.transpose() method

The returned array holds a reference to the original one, and thus is a view of it (not a copy). If the content of the original array changes, the content of the view array too. The view can be written if the underlying array is writable.

Note that I/O performance in such a transposed view might be poor.

This is the same as the C function GDALMDArrayTranspose().

Returns
  a new array, that holds a reference to the original one, and thus is a view of it (not a copy), or nullptr in case of error.

The documentation for this class was generated from the following files:

- gdal_priv.h
- gdalmultidim.cpp