The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
265 
are the original image and pan-sharpened image using ESR1 
pan-sharpening algorithm. 
Figure 4. A multi-band image at a resolution of 2.8 meters 
Figure 5. Pan-sharpened result using ESRI pan-sharpening 
method with a panchromatic image of 0.7 meter resolution. 
4. ARCOBJECTS RASTER API 
ArcGIS software is built upon ArcObjects, which includes APIs 
that support the built-in raster functionality. Developers and 
third parties can also extend ArcGIS raster capabilities using the 
existing APIs and build application for visualizing, processing, 
and analyzing raster data. ArcObjects contain four major classes 
that support the open structure for custom image processing: 
RasterDataset, Raster, GeodataXFrom and PixelFilter. 
Figure 6. Diagram of key classes supporting raster functionality 
A RasterDataset class is used to read raster files and provide 
properties about the raster data. The RasterDataset class 
encapsulates all the details that handle reading specific raster 
formats and provides an easy data access, for developers, of 
raster data in different formats. Regardless of the raster formats, 
RasterDataset interprets information of the raster data 
automatically such as projection, coordinates, statistics of the 
pixel values, colormap, and pyramids. A RasterDataset can be 
created directly from the raster file name through a workspace 
class (e.g. name of the directory where the raster file resides). 
The Raster, derived from a RasterDataset, is a class that 
provides access to raster data and handles pixel read from raster 
dataset. Raster is a virtual representation of raster dataset which 
allows changing the properties of Raster such as dimension, 
extent, spatial reference, and so on. It also allows transforming 
the raster data geometrically and radiometrically through the 
GeodataXForm and PixelFilter classes. The changes on Raster 
is virtual, it can be preserved by saving out to another raster 
dataset or passing to display pipeline. 
4.1 ADDING CUSTOM GEODATA XFORM TO ARCGIS 
Figure 9. Diagram of geodata transformation classes 
The GeodataXform is an abstract class that consists of many 
geometric transformation classes including polynomial 
transformation, rubber sheeting transformation, RPC 
transformation (Rational Polynomial Coefficients), coordinate 
transformation that supports projecting raster, and Spline 
transformation. (Figure 9) 
All geodata transformation classes support IGeoDataXform 
interface and three additional interfaces: IClone, 
ISupportErrorlnfo, and IPersistStream. IGeodataXform 
interface contains methods that transform a set of points, 
transform an area, and transform a cell size, which provide the 
foundations to transform raster data geometrically. 
GeodataXform is designed to work with class Raster. Once it is 
set on Raster, the ArcGIS raster transformation pipeline, 
through RasterXFormer class, will detect it and apply the 
GeodataXform during pixel fetching for display or data output. 
To add a custom transformation into ArcGIS framework, create 
a custom geodata transformation class by implementing 
IGeoDataXform and the rest three required interfaces. Once 
plug-into ArcGIS, the custom geodata transformation class will 
work as same as any other built-in geodata transformation 
classes, e.g. it can be applied to Raster using 
IRaster2::GeoDataXform method and displayed in ArcMap 
directly. A geodata transformation class can also be serialized 
and stored in a XML file as part of raster dataset. 
Any third parties, who wish to support their proprietary camera 
model in ArcGIS, can take advantage of this open structure. 
For further documentation and example, please refer the online 
topic: 
http://edndoc.esri.com/arcobjects/9.2/CPP_VB6_VBA VCPP_ 
Doc/COM_Samples_Docs/Raster/Transformation_And_Spatial 
_Reference/CustomGeoXForm/954B42BC-A74C-45C9-9BB9- 
A2A2006AF573.htm