GDALWarpOperation Class Reference
#include <gdalwarper.h>
List of all members.
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Public Member Functions |
CPLErr | Initialize (const GDALWarpOptions *psNewOptions) |
const GDALWarpOptions * | GetOptions () |
CPLErr | ChunkAndWarpImage (int nDstXOff, int nDstYOff, int nDstXSize, int nDstYSize) |
CPLErr | ChunkAndWarpMulti (int nDstXOff, int nDstYOff, int nDstXSize, int nDstYSize) |
CPLErr | WarpRegion (int nDstXOff, int nDstYOff, int nDstXSize, int nDstYSize, int nSrcXOff=0, int nSrcYOff=0, int nSrcXSize=0, int nSrcYSize=0) |
CPLErr | WarpRegionToBuffer (int nDstXOff, int nDstYOff, int nDstXSize, int nDstYSize, void *pDataBuf, GDALDataType eBufDataType, int nSrcXOff=0, int nSrcYOff=0, int nSrcXSize=0, int nSrcYSize=0) |
Detailed Description
High level image warping class.
Warper Design
The overall GDAL high performance image warper is split into a few components.
- The transformation between input and output file coordinates is handled via GDALTransformerFunc() implementations such as the one returned by GDALCreateGenImgProjTransformer(). The transformers are ultimately responsible for translating pixel/line locations on the destination image to pixel/line locations on the source image.
- In order to handle images too large to hold in RAM, the warper needs to segment large images. This is the responsibility of the GDALWarpOperation class. The GDALWarpOperation::ChunkAndWarpImage() invokes GDALWarpOperation::WarpRegion() on chunks of output and input image that are small enough to hold in the amount of memory allowed by the application. This process is described in greater detail in the Image Chunking section.
- The GDALWarpOperation::WarpRegion() function creates and loads an output image buffer, and then calls WarpRegionToBuffer().
- GDALWarpOperation::WarpRegionToBuffer() is responsible for loading the source imagery corresponding to a particular output region, and generating masks and density masks from the source and destination imagery using the generator functions found in the GDALWarpOptions structure. Binds this all into an instance of GDALWarpKernel on which the GDALWarpKernel::PerformWarp() method is called.
- GDALWarpKernel does the actual image warping, but is given an input image and an output image to operate on. The GDALWarpKernel does no IO, and in fact knows nothing about GDAL. It invokes the transformation function to get sample locations, builds output values based on the resampling algorithm in use. It also takes any validity and density masks into account during this operation.
Chunk Size Selection
The GDALWarpOptions ChunkAndWarpImage() method is responsible for invoking the WarpRegion() method on appropriate sized output chunks such that the memory required for the output image buffer, input image buffer and any required density and validity buffers is less than or equal to the application defined maximum memory available for use.
It checks the memory requrired by walking the edges of the output region, transforming the locations back into source pixel/line coordinates and establishing a bounding rectangle of source imagery that would be required for the output area. This is actually accomplished by the private GDALWarpOperation::ComputeSourceWindow() method.
Then memory requirements are used by totaling the memory required for all output bands, input bands, validity masks and density masks. If this is greater than the GDALWarpOptions::dfWarpMemoryLimit then the destination region is divided in two (splitting the longest dimension), and ChunkAndWarpImage() recursively invoked on each destination subregion.
Validity and Density Masks Generation
Fill in ways in which the validity and density masks may be generated here. Note that detailed semantics of the masks should be found in GDALWarpKernel.
Member Function Documentation
CPLErr GDALWarpOperation::Initialize |
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const GDALWarpOptions * |
psNewOptions |
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This method initializes the GDALWarpOperation's concept of the warp options in effect. It creates an internal copy of the GDALWarpOptions structure and defaults a variety of additional fields in the internal copy if not set in the provides warp options.
Defaulting operations include:
- If the nBandCount is 0, it will be set to the number of bands in the source image (which must match the output image) and the panSrcBands and panDstBands will be populated.
- Parameters:
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| psNewOptions | input set of warp options. These are copied and may be destroyed after this call by the application. |
- Returns:
- CE_None on success or CE_Failure if an error occurs.
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The documentation for this class was generated from the following files:
Generated on Thu Apr 14 10:01:36 2005 for GDAL by
1.4.2