| Digital Ortho: Texas Orthoimagery Program: DOQQ Processing Techniques and Applications for the State of Texas
By Karen Steede-Terry and Andy S. Bury Project History
By the early 1990s, GIS in Texas had become fairly widespread and GIS software was a common tool used for decision making in many state agencies. The need for ubiquitous, low cost data had become evident, so a "Texas GIS Planning Council" was formed to find solutions to this common problem. In November of 1994, through a resolution passed by the Planning Council, an innovative partnership was formed between the USGS, state and local agencies and private industry to fund the production of Color Infra-Red (CIR) digital orthophoto quarter quadrangles (DOQQs) statewide.
Primary funding for the effort, named the Texas Orthoimagery Program (TOP), was provided by the U.S. Geological Survey (USGS) and the Texas Department of Information Resources (DIR). However, the project could only be a success with additional funding provided by other participating state agencies, local governmental agencies, and private industry. At the regional level, the DIR solicited contributions from Councils of Governments (COGs); organizations specific to Texas that address the needs of several counties. The COGs organized local contributions, provided matching funds, and acted as the sponsor for their individual region. The project is one of the largest cooperative agreements to date with the USGS, involving over 52 counties, and 2,974 DOQQs, with additional DOQQs to be produced at a later date. The Process
The DIR, on behalf of the Texas GIS Planning Council, contracted with a mapping consortium headed by VARGIS LLC of Herndon, Va. VARGIS is the Texas DOQQ Project Primary Contractor, providing overall project management and quality control. VARGIS manages a consortium of eight photogrammetric firms for the production of the raw DOQQs. The consortium includes Woolpert of Dayton, Ohio and Dallas, Texas; Photo Science Inc. of Gaithersburg, Md.; Vernon F. Meyer and Associates of New Orleans, La.; ADR and Associates of Pensauken, N.J.; Tobin Surveys of San Antonio, Texas; United Aerial Mapping of San Antonio, Texas; Horizons Inc. of Rapid City, S.D. and Rust Lichliter Jameson of Austin, Texas. Control work for the project is performed by the Texas Department of Transportation. After the DOQQs are produced by the photogrammetric firms and a quality assurance performed by VARGIS, they are shipped to Earth Information Systems Corp. (EISYS), in Austin, Texas for resampling and distribution.
To create DOQQs, the photogrammetric firms begin with aerial photography acquired from the USGS National Aerial Photography Program (NAPP), flown in 1995 and 1996. These photographs are then scanned and rectified to remove distortion, in order to create DOQQ data. Next, the DOQQs are delivered to EISYS on tape and processed through a custom production system, quality checked (QC'd), then written to master CDs. The CDs are duplicated in-house at EISYS and labeled in accordance to their geographic area. The DOQQs are distributed in four standard spatial resolutions (1-meter, 2.5-meter, 10-meter and 30-meter), in both 24-bit and 8-bit color, and in GeoTIFF format. The data come standard in UTM projection, NAD83 datum, GRS80 and in units of meters, and can be transferred into any projection for an added cost. Product Specifications
Until a few years ago, only large, expensive systems had the storage space, processing speed, and memory needed to manage and manipulate high-resolution images. Today, with the advent of Pentium chips, reduced cost of increased disk storage, and 4X to 15X speed CD-ROM readers, even the largest DOQQ files are easily accessible. One quarter quad of 1m, 24bit CIR data uses 158Mb of disk space. However, the 2.5m, 8bit data uses only a little over 8Mb, and the lower resolutions of 10m and 30m data, even less. One CD can hold up to 650 Mb of data, so depending on the resolution, a different number of quads are contained on each disk.
Up to four quarter quadrangles are written to each 1-meter CD, up to 64 quarter quadrangles to each 2.5-meter CD, and an entire order area (see Figure 2 for Order Area Delineations) of quad mosaics are written to each 10 and 30-meter CD. In addition, each 1m CD contains a quadrant of digital elevation model (DEM) data and each 30m CD contains all of the DEM data for the entire order area. All of these data, in any combination, are available at a cost of only $75 per CD. If storage space is an issue, or reading a CD is a problem, the data can be provided via FTP, or on other medium such as digital tape, or hard-copy plots.
The data can be viewed directly from the CD via a "DOQQ Viewer Tool," which comes standard on each CD, so that the user does not have to have their own browser software. The viewer, written in ESRI's Map Objects programming module, allows a user to pan and zoom, but does not have the increased functionality of other software tools. For this reason, the data are also compatible in the following formats: ArcView, ARC/INFO, IMAGINE, Intergraph, Bentley, PCI, Adobe Illustrator, Pagemaker, ER Mapper, Lview, Map Info, and AutoCAD Map; basically any software that can read TIFF files. Advantages of DOQQ Data
High resolution, digital orthophotos provide a rich source of information for a GIS. They provide complete, accurate, current, and more comprehensive information than traditional methods of GIS data input, such as digitizing vectors from maps. In addition to displaying DOQQs as a basemap or backdrop for preexisting vector data, they can be used to generate new data through on-screen, heads-up digitizing and photointerpretation.
DOQQ data, available in both high and low resolution, provides the user with a choice of detail and/or display speed. The 1-meter data provides a detailed view of the ground and excellent color discrimination, while the lower resolution products allow for faster draw times and require less disk space. Because the 1-meter resolution DOQQ data come in quarter-quadrangle pieces, they are more manageable than loading a typical 180MB satellite image scene. Not only are they easier to work with than large satellite imagery, but the DOQQ data are higher resolution and much less expensive than the 2-5 meter satellite image data currently available.
The 1995 and 1996 DOQQ data often provide information where none existed before. Where data do exist, their source is usually pre-1995, such as USGS 1984 or older quad maps. Considering this, the DOQQs provide a more detailed and "information rich" source of data for GIS analysis, as well as more current data.
All modern datasets, such as the Texas DOQQs, should be accompanied by an associated metadata file. In this regard, the DOQQ data come with a complete set of Federal Geographic Data Committee (FGDC) compliant metadata files. This allows state agencies and other organizations using the data to instantly comply with the current Federal Geographic Data Standards. In addition, DOQQs meet industry standards for photogrammetric mapping, including "National Map Accuracy Standards" as established by the U.S. Department of the Interior and "Standards for Digital Orthophotos" as established by the USGS National Mapping Division. Applications
The accuracy of the digital orthoimages is useful when identifying features and logging them into a GIS database. A good example of this is pipeline management and routing applications. Planning a pipeline right-of-way through a landowner's property requires a high degree of accuracy. Often, the landowner will only provide a narrow corridor through which the pipeline should pass. The increased accuracy of 1-meter data can provide the information needed to minimize environmental impact while keeping pipeline construction costs to a minimum.
One common problem for many potential GIS users is the lack of data for an area. Many applications require data for areas in which local data is nonexistent. Precision farming is a good example of an application which requires a very detailed base map. Farmers need digital maps of their fields in order to take full advantage of new technologies such as GIS and GPS (Global Positioning Systems). DOQQs provide instant base maps for a farm, ranch, or any application at a reasonable cost. From DOQQs, property lines, field boundaries, drainage systems, soil delineation and landcover or crop cover can be determined for GIS analysis.
In the same way, DOQQs can be used by the Forest Service and large paper companies for forest planning. The accuracy and information content of a CIR DOQQ can be used for timber harvest counts and for assessing the health of trees. The imagery provides detail that can be used for determining crown closure or for counting individual crowns, if necessary. An inherent quality of CIR can reveal a tree's health as well. In CIR DOQQs, healthy trees are shown as red and vigorous, while unhealthy trees are gray or brown. Within a modern forest, mapping and planning logging roads, forest stand mapping and habitat analysis are increasingly important. Building an efficient road network, obtaining accurate acreage and timber inventories and being sensitive to endangered species habitats are all important because inefficiency, overlooked timber, and environmental litigation equals money lost. The DOQQs can provide an excellent source of information for these applications as well.
DOQQ imagery is also useful in the arena of urban development. For instance, DOQQ orthoimagery is very good for identifying water features (See Figure 1). This allows DOQQs to be used for identifying wetlands to be avoided in areas of potential development. If wetlands cannot be avoided, the DOQQs can also be used to create accurate maps for environmental remediation. Similarly, floodplain maps can be overlaid on DOQQs to determine if areas of construction or existing development fall within a floodplain. Construction permits can then be issued based on the results of these findings and insurance companies can determine if prospects and existing customers need flood insurance. User Model
In Texas, all post office boxes and rural routes are required to be "re-addressed" to a street name and number (e.g. 123 Main Street) for the purposes of 911 emergency routing. Routing emergency vehicles requires a dispatch address to match a street address in the GIS database, otherwise P.O. boxes and rural routes will not match the database when geocoding is performed. This effort is primarily being coordinated for all 254 counties in Texas through the COGs, or Council of Governments mentioned earlier.
GeoSYS Inc., located in Angleton, Texas, is responsible for developing the 911 Emergency routing GIS in Brazoria County and needed to develop new digital road vectors in an accurate and cost-effective manner. Using DOQQs as a basemap, primary highways, secondary highways, light-duty roads and unimproved road centerlines were "heads up" digitized. Existing road vectors, digitized from local map data, were overlayed and compared to the DOQQs (See Figure 3). Any discrepancies between the existing road vectors and the DOQQs were either fixed or noted in an error database for future editing. The new road centerlines were given address ranges and other attributes in preparation for 911 emergency routing, and combined with the existing road centerline database. This process provided an extremely accurate road centerline database for 911 emergency response. GeoSYS also purchased a full set of DOQQs for Brazoria County, one of the first areas to be processed in Texas. This allowed display of the 911 road vectors over a detailed backdrop and provided a rich source of data for future projects.
The Texas Orthoimagery Program has been hailed as the answer to obtaining accurate and up-to-date data for Texas GIS databases. Jim Stevens, president, GeoSYS, commented that the "DOQQ imagery proved tremendously helpful, not only in completing 911 road centerlines, but also as a resource for our land parcel boundary database." As stated, the data are highly versatile, and can be used for a wide range of applications, including several not mentioned in this article. The data can also be used in conjunction with storm water management, transportation , groundwater protection, and public utilities. By working together for a common effort, the goal of low-cost, highly accurate digital data has been realized for the state of Texas. About the Authors:
Karen Steede-Terry is a GIS, GPS, and marketing consultant based in Austin, Texas. Andy S. Bury is DOQQ Project Manager, Earth Information Systems (EISYS), Austin, Texas. He may reached at 512-329-5577. Back |
