The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
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does it require the orthoimagery at high resolution. Even 
parameters such as mosaic seamlines are not dependant on the 
requirement for orthoimage with final accuracy, Most of the 
dataflow and production bottlenecks can be alleviated by using 
geodatabase and server centric workflows. 
2. INTRODUCTION TO ARCGIS IMAGE SERVER 
ArcGIS Image Server is a product from ESRI that provides 
management, processing, and dissemination of very large 
volumes of imagery with on-the-fly server based processing. 
This product can serve traditional pre-processed image tiles, 
and serve imagery that has not be pre-processed. The required 
processing is applied in real time as the imagery is being served. 
The processing to be applied is defined in a database. This 
enables the same imagery to be served in different forms, as 
required by different users, without additional data storage. 
Also, the imagery can remain in its native or original form 
removing the requirement to convert the data. Additionally, the 
image products can be served as virtual mosaics. When an 
image is requested, the server not only extracts the required 
pixels, but applies the required processes, returning the pixels as 
well as the metadata to the user’s application. 
As with the other ArcGIS Server family of products, the 
workflow is defined in three stages: Author, Serve, and Use. 
2.1 Author 
In authoring an image service definition database is created, 
which defines a catalog of all the imagery. This image service 
definition contains information on each of the individual images 
including all properties, metadata, footprint, and location. The 
large volume of pixel data are not loaded into the database, but 
remain in their original form and are referenced. Also, 
associated with each image are the properties of how the images 
should be processed. These include the processes to be applied 
and the parameters of the processes. Such processing can 
include how to radiometrically enhance the images as well as 
how to process the image geometrically. A geometric process 
for georeferencing can be a simple affine transform or more 
complex transforms such as orthorectification that is dependant 
on camera calibration information, orientation data, and a 
reference to an elevation model. Associated with each image is 
a footprint shape that defines the extent of the pixels to be used, 
enabling the exclusion of pixels that represent the data frame of 
a scanned image or exclusion of areas such as clouds. The same 
set of images can be included in different image sendee 
definitions enabling different imagery products to be defined 
with no additional imagery being stored. Such products could 
include, different band combinations or enhancements that 
utilize the multispectral capabilities of many digital sensors. 
Central to ArcGIS Image Server is the image service definition 
that defines within a database structure the processing to be 
performed on the imagery as well as all the parameters that 
effect the processing. As processes and parameters become 
available in the production flow they can be added or modified 
within the image service. The service definition consists of both 
processes defined using XML as well as the parameters of these 
processes defined either within the XML or as attributes of the 
service tables. This provides great flexibility and enables the 
database table to define only those parameters that may change. 
For example, parameters such as interior orientation that do not 
change can be defined as constants in the XML while 
parameters such as the six external orientation parameters can 
be defined in the tables. These orientation parameters may be 
defined initially from the GPS and flight navigation data and be 
updated when the GPS/IMU parameters are available, then 
updated after an aerial triangulation is performed. 
The open and documented data structures used enable simple 
integration of these parameters from a wide range of existing 
applications that perform such parameter determination. This 
enables ArcGIS Image Server to be quickly integrated into 
existing workflows. 
2.2 Serve 
The image service definition can be published on the server and 
then is simultaneously accessible to many different client 
applications. These applications can either connect directly to 
ArcGIS Image Server using RPC (Remote Procedure Calls) or 
through standards such as OGC WMS, WCS as well as SOAP 
and REST by serving through ArcGIS Server. These enable a 
large range of client applications to access the imagery as 
services, either over local area networks or over the web. 
2.3 Use 
Clients connecting to image services can view the imagery as a 
large, single image; although they often consist of thousands of 
individual images. Importantly, metadata about the image 
service as well as the individual images being viewed can be 
accessed, providing the client with information about the 
imagery that is critical to many decision making tasks. The 
client applications can also interact with the image services to 
dynamically refine the processing. For example, a client may 
change the order of overlapping imagery to obtain imagery that 
more closely matches their requirement, such a being closer to a 
specified date or having a required sun elevation. When 
working over low bandwidth connections, a client can change 
the compression used for the data transmission. The 
compression used for the data transmission is therefore 
independent of the compression used to store the data, enabling 
an analysis, for example, to use highly compressed imagery for 
faster navigation, while still being able to reduce or remove the 
compression for detailed analysis. Therefore, the required 
image product can be created on demand, based on parameters 
defined in the database or specified by the client application. 
3. PROCESSES 
For all requests, the multiple geometric processes such as 
orthorectification, reprojection, pan-sharpening, and mosaicking 
are concatenated internally by ArcGIS Image Server to a single 
sampling of the original imagery. As a result, the quality of the 
resulting pixel data is improved. Prior to sampling the imagery 
the geometry is analysed such the only the pixels required for 
processing are read, therefore, the volume of data to be read 
and processed is substantially reduced. Typically, with aerial 
imagery being flown with high overlaps only a small 
percentage of the original pixels may be needed in the final 
product and require processing. Performing pan-sharpening on- 
the-fly without the need to store the large pan-sharpened file 
also substantially reduces data volumes.