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April - June 2006
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Leverage Imagery in ArcGIS

Data visualization is a key component of the geographic advantage that GIS provides. Raster data is an important GIS data source that aids visualization.

Raster data, whether imagery or grids, represents geographic features as a pattern of discrete cells called pixels. Grid data can be thematic data that classifies a phenomenon, such as soil type or land use, or represents continuous data about a measured quantity such as elevation. Raster data can also be imagery or pictures that convey additional information about map features.

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ArcGIS is a comprehensive platform for using imagery.

Popular imagery data sources include aerial photographs, satellite imagery, photographs, scanned documents, and maps. Aerial photographs and satellite imagery can document conditions for a large area at a fixed time for relatively low cost. Georeferenced and used as a backdrop for vector data or draped over a terrain model, imagery lets users more quickly and easily locate features and understand geospatial relationships. Because image data is captured in a discrete time frame, it creates an historical record that is useful for identifying where and when change has occurred.

When geometrically corrected to remove distortions caused by relief displacement, camera tilt, lens distortion, or other factors, remotely sensed data can serve as the source for spatially accurate data.

Both aerial photographs and satellite scanners can detect light transmitted at wavelengths not visible to the human eye. These spectral ranges can furnish information that would not otherwise be available about crop health, new building in violation of local codes, and other change detection applications in a timely manner.

Linking photographs, scanned documents, and maps to geographic locations provides a framework for organizing data and a context for accessing and understanding related information. Just as tabular data is better understood within a geospatial framework, so photographs, scanned documents, and maps can be more efficiently used within a geographic context.

ArcGIS is an integrated collection of software products that delivers a system for storing, managing, analyzing, and serving imagery. These software products include ArcGIS Desktop; ArcSDE; and the ArcGIS extensions designed for visualizing and analyzing image data, ArcIMS and ArcGIS Server. With ArcGIS, users can utilize and manage raster data within a common framework that maximizes performance and streamlines workflows.

ArcGIS improves data management by storing raster and vector data types within the same framework. Costs associated with duplicated datasets are reduced, and raster data is more effectively used because it can be served from a central repository to many users across an organization. ArcGIS tools, such as raster catalogs and mosaics, improve raster data retrieval and display performance. The ability to append raster data to geodatabase features allows this data source to be more extensively used.

ArcGIS Desktop (ArcView, ArcEditor, and ArcInfo) furnishes a user interface for managing imagery. With the tools in ArcGIS Desktop, users can create, manage, and visualize libraries of raster and imagery data. It furnishes tools within a common framework for generating image footprints, publishing metadata, and searching large raster collections based on any combination of geographic extent, content, data format, or keyword. ArcGIS Desktop also contains tools for merging raster datasets and storing them in a continuous data layer.

Esri's spatial database gateway, ArcSDE, manages access to raster data and related metadata stored in IBM DB2, Informix, Microsoft SQL Server, and Oracle relational DBMS. ArcSDE enables fast, online, multi-user access to raster data throughout an organization.

By loading data into ArcSDE, users can manage large images and take advantage of storing raster data using indexing, tiling, pyramids, and compression for better display performance. Partial pyramid updates allow quick revision of imagery already stored in the database. With ArcSDE, imagery data can be used simultaneously by desktop applications, Internet mapping servers, and custom applications built with ArcGIS Engine.

The ArcGIS Spatial Analyst, ArcGIS 3D Analyst, and ArcScan for ArcGIS extensions work directly within the ArcGIS Desktop, ArcGIS Engine, and ArcGIS Server environments. These extensions supply enhanced display, analysis, and data capture capabilities for raster and imagery data. ArcGIS extensions ensure file format compatibility and do not require third-party products for optimizing raster display and analysis. This saves both time and money.

ArcIMS and ArcGIS Server provide complementary solutions for serving GIS functionality, maps, and data (including features, imagery, and metadata) over the Web. ArcIMS' highly scalable framework for GIS Web publishing works with a wide range of clients that includes custom Web applications, ArcGIS Desktop, and mobile devices. Data can be distributed and shared across an organization or the world. With ArcIMS metadata services, metadata can be published along with thumbnail images to Web sites.

ArcGIS Server is a comprehensive platform for delivering enterprise GIS applications that are centrally managed and support multiple users. It provides the framework to build and deploy server-based GIS applications that allow users to create, query, and analyze cell-based raster data.

Articles in the Focus section of this issue of ArcUser magazine illustrate the use of imagery data directly on ArcGIS Desktop or shared over the Web.

Staff members of Ayres Associates Inc. combined mobile GIS and photographs to identify and document geological features as part of work for an area drainage master study. The images of alluvial fan edges and drainage features were georeferenced to the other layers in the GIS so they could be intelligently referenced by geologists and engineers during the subsequent phases of the project and used to explain why geology was interpreted in a certain way.

An intranet application created by the GIS department of Pierce County, Washington, gave casual GIS users access to the county's collections of orthophotography and color infrared imagery. The Ortho Viewer, built using ArcIMS, ArcSDE, Microsoft SQL Server, and ColdFusion MX, is helping users from departments across the county make use of this valuable but previously underutilized resource.

A project sponsored by the Khaled bin Sultan Living Oceans Foundation is capturing detailed information about threatened coral reefs using a Compact Airborne Spectrographic Imager.

For more information on working with raster data, see Working with Rasters in ArcGIS 9, Storing Raster Data in an ArcSDE Geodatabase, Georeferencing Rasters in ArcGIS, and other courses developed for the ArcGIS Spatial Analyst, ArcGIS 3D Analyst, and ArcScan for ArcGIS extensions available from the Esri Training and Education.

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