Functions that alter the properties of an ST_Raster value

The ST_Raster type functions that alter properties must be used as part of SQL UPDATE statements. All of these functions require that an ST_Raster value already exist in the table.

Build pyramids

Pyramids are used to improve performance. They are a downsampled version of the original raster dataset and can contain many downsampled layers. Each successive layer of the pyramid is downsampled at a scale of 2:1. Below is an example of two levels of pyramids created for a raster dataset:

Use the ST_Raster buildPyramids function to create a pyramid on an ST_Raster value. The buildPyramids function builds reduced-resolution pyramids.

Create a color map

A color map is a set of values that are associated with colors. Color maps are used to display a single-band raster consistently with the same colors. Each pixel value is associated with a color, defined as a set of red, green, and blue (RGB) values. Since each value has a distinct color associated with it, it will always display the same way each time you open it in a program that can read a raster with a color map. Color maps are capable of handling up to 16-bit data.

Use the ST_Raster setColormap function to apply a color map to a single-band 8- or 16-bit ST_Raster value. The setColormap function uses a TIFF image file as input to create the color map.

Calculate raster statistics

Raster statistics are used by ArcGIS Desktop and geoprocessing operations to classify data. They are also used by the ArcGIS display renderer to stretch the data. Some data needs to be stretched to make it discernable.

If statistics are present, ArcGIS automatically applies a stretch of two standard deviations. If the statistics are not present, the ArcGIS Desktop display renderer will not stretch the data.

If you want to calculate raster statistics on an ST_Raster value using SQL, you can use the buildStats function.

Mosaic to an ST_Raster value

The mosaic operation merges two or more images. (See What is a mosaic? for more information on mosaics.)

You can use the mosaic operation to mosaic georeferenced TIFF files to an ST_Raster value or to get the pixel data values from an existing ST_Raster value and mosaic them to another ST_Raster value.

Note:

Before you mosaic raster data to an existing value, you must remove the color map, if one is present. You can reapply the color map after the mosaic operation is finished.

Remove a color map from an ST_Raster value

As mentioned in the previous section, you must remove the color map from your ST_Raster value before you can mosaic more data into it.

Use the ST_Raster deleteColormap function to remove a color map from an ST_Raster value.

Remove statistics from an ST_Raster value

Statistics allow the ArcGIS Desktop renderer to stretch raster data. For some data, such as color-corrected rasters, stretching distorts the image. If you calculate raster statistics on an ST_Raster value, then find the image is distorted when rendered in ArcGIS Desktop, you can remove the statistics from the raster value.

Use the ST_Raster deleteStats to remove statistics from an ST_Raster value using SQL.

Crop an ST_Raster value

Cropping removes all raster data beyond the extent that you specify for the raster. If you only need a portion of the raster value, you can use the ST_Raster crop function to reduce the raster value to only the required extent.