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Mosaicking images into a large raster dataset with a pyramid can take a long time for ArcSDE 9.2 and 9.3. This can happen even if the extent of raster data source is below and to the right of the raster dataset's image origin.
A logic problem introduced at ArcSDE 9.2 causes the raster dataset's pyramid to be rebuilt.
To understand the cause of this problem, the concept of the image origin and the block origin must first be explained.
The image origin is the coordinate reference point of the raster dataset. It is set to the upper left coordinate raster dataset's extent. The image origin moves as raster data sources that are above or to the left of the raster dataset's extent are mosaicked to the raster dataset.
The block origin is the coordinate reference point that is used to number the blocks (also called tiles) in the raster blocks table. Unlike the image origin, once the block origin is established, it does not change. By default, the block origin is set to the image origin after the first raster data source is added to the raster dataset. Alternatively, the block origin can be present at the creation of the raster dataset. (On the ArcCatalog and ArcToolbox user interfaces, the preset block origin is referred to as the pyramid reference point.)
A mosaic operation that moves the raster dataset's image origin up or to the left triggers a pyramid rebuild if the new image origin is also above or to the left of the block origin. Presetting the block origin to a point that is known to be above and to the left of the ultimate image origin of the raster dataset avoids the expensive pyramid rebuild.
However, a mosaic operation the does not move the image origin should not trigger a pyramid rebuild. Alternatively, a logic error introduced during the ArcSDE 9.2 release triggers the pyramid rebuild when all of the following conditions are true:
1. The extent of the raster dataset does not change as a result of the mosaic operation.
2. The block origin was not preset (e.g., the pyramid reference point was not set).
3. The extent of the mosaicked raster data source is completely above and to the left of the block origin.
Move the block origin to the image origin. That can only be accomplished either by copying the existing raster dataset to a new raster dataset or by reloading the raster dataset with the pyramid reference point set to the current raster dataset's image origin.