Frequently Asked QuestionsWhere can I find 2009 1-meter Compressed County Mosaic (CCM) Orthoimagery?
A limited number of raw CCM zip files have been made available through DAS/GEO - State of Oregon's FTP site. The data can be accessed through Oregon Imagery Explorer's Available Imagery page.
When will the 2009 half-meter Orthoimagery be available?
We will have it online and accessible by fall 2010.
I would like to have a large portion of the Oregon imagery (for example, several counties). May I ship an external hard drive to you and have the data copied onto it?
You may download the imagery for an entire county at our County Downloads page. For larger areas, please contact the GIS Data Administrator at the Oregon Geospatial Enterprise Office (GEO) for other options. For contact information, please see the GEO Web site.
I know the imagery was flown in the summer of 2005, but how do I find out the exact dates for the various Digital Orthophoto Quadrangles (DOQs)?
The photos were taken between 6/29 and 8/15 of 2005. For more information on the dates for the various DOQs, please see the zipped shapefile.
Why is the color of the orthoimagery so different than how it appears in Google?
We do not know Google's process for building their mosaic from the uncompressed orthoimagery. We suspect they do color balancing etc. over the entire dataset prior to making available to the public.
Are there any restrictions to the data or use of the data?
The data from the Oregon Imagery Explorer is freely available to the public (unless otherwise noted) and may be distributed or copied. We request that the following statement be used when citing, copying, or reprinting the data: “Data available from the Oregon Imagery Explorer.”
There are no constraints to using to data. However, users should be aware that temporal changes may have occurred since this data set was collected and that some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.
I am using the imagery in a map. How should it be attributed?
The following statement should be used when citing, copying, or reprinting Oregon aerial imagery data: "Data available from the Oregon Imagery Explorer." For more information on using the imagery data, please see the Data Disclaimer page.
Although the 2005 half-meter orthoimagery in the Image Extraction Tool has undergone ECW 9:1 compression, it may be uncompressed and extracted as a geoTIFF. Additionally, the compressed imagery may be uncompressed and compressed at different compression ratios in JPEG, JPEG2000, or ECW format.
You may select the following export formats:
a. Baseline geoTIFF (.tiff) with world file (.tfw) with no tiling and no JPEG compression
b. JPEG (.jpg) with world file (.jgw)
c. GeoJP2/JPEG 2000 (.jp2) with world file (.j2w)
d. ER Mapping ECW (.ecw)
Can a projection be specified when downloading?
Yes, you may choose to reproject the imagery from geographic coordinates (WGS84) to other projections.
You may select the following projections:
a. UTM Zone 10N using NAD27 or NAD83
b. UTM Zone 11N using NAD27 or NAD83
c. Oregon State Plane North and South using NAD27or NAD 83
d. Oregon State Plane North and South using NAD 83 HARN
e. NAD83 Oregon Lambert (ft)
f. NAD83 HARN Oregon Lambert (ft)
g. Geographic in WGS84
What is Oregon 2005 half-meter orthoimagery?
The original Oregon 2005 half-meter orthoimagery is in Digital Orthophoto Quadrangle (DOQ) format and has a spatial resolution of a half-meter. The original DOQs are computer-generated images that have been reconstructed from aerial photographs acquired in the summer of 2005.
The specifications for the original imagery are:
Product | Spatial Resolution | Projections | Formats | Horizontal Accuracy |
Oregon 2005 half-meter DOQs | Half-meter | Geographic coordinates (GCS83), UTM zone 10 or 11, Oregon State Plane, or Oregon Lambert | Uncompressed geotiff, compressed MrSID | Within +/- 5 meters of the 1992 USGS DOQ imagery. |
Table 1: Original DOQ specifications
For more information on the original Oregon 2005 half-meter DOQs, please see the Oregon Geospatial Enterprise Office (GEO) Oregon Orthoimagery Framework Group Web page: http://gis.oregon.gov/DAS/EISPD/GEO/fit/orthoimagery/OrthoFrame.shtml.
A statewide mosaic of the original DOQs has been reprojected into geographic coordinates (WGS84) and has undergone ER Mapper Compressed Wavelet (ECW) compression at an 18:1 and 9:1 ratio.
The specifications for the mosaic for viewing and streaming are:
Product | Spatial Resolution | Projections | Formats | Horizontal Accuracy |
Oregon 2005 half-meter statewide mosaic for viewing and streaming | Half-meter | Geographic coordinates (WGS84) | Compressed 18:1 ER Mapper ECW | Within +/- 5.75 meters of the 1992 USGS DOQ imagery. |
Table 2: Compressed Mosaic specifications
The specifications for the mosaic for extraction are:
Product | Spatial Resolution | Projections | Formats | Horizontal Accuracy |
Oregon 2005 half-meter statewide mosaic for extraction | Half-meter | Geographic coordinates (WGS84) | Compressed 9:1 ER Mapper ECW | Within +/- 5.75 meters of the 1992 USGS DOQ imagery. |
Table 2: Compressed Mosaic specifications
The specifications for the extracted imagery are:
Product | Spatial Resolution | Projections | Formats | Horizontal Accuracy |
Oregon 2005 half-meter extracted imagery | Half-meter | Geographic coordinates (WGS84), UTM zone 10 or 11, Oregon State Plane, or Oregon Lambert | ECW, geoTIFF, GeoJP2/JPEG 2000, or JPEG
| Within +/- 5.75 meters of the 1992 USGS DOQ imagery. |
Table 3: Extracted imagery specifications
If the extracted imagery specifications do not meet your needs, please contact the Oregon Geospatial Enterprise Office.
What is imagery compression?
Imagery compression reduces the image file size by changing the content and organization of the data within the file (USDA, 2006.) Whether or not the image can be restored to its original condition depends on whether a lossless or lossy compression technique was used.
Lossless compression techniques, as the name implies, allow image compression without any loss in information. Therefore lossless techniques allow for a perfect reconstruction of the original image. Lossless compression is used for archiving or other circumstances when you want to keep all the original data at a lower compression rate.
Lossy compression introduces a loss in information. How much information is lost usually depends on the compression ratio and the compression algorithm. Lossy techniques do not allow for the original image to be perfectly reproduced. However, when the differences between the original and reconstructed images are either not noticeable or do not significantly affect the image quality, lossy techniques might be considered “visually lossless” which is a subjective, not mathematical, term.
When working with imagery, including orthoimagery and satellite imagery, the size of image files can become very large. Compression of imagery not only reduces image file size, but also allows for faster access and easier distribution.
For example, the Oregon 2005 half-meter imagery is approximately 4.1 terabytes in total size. Without compression, you would not be able to access this high-resolution imagery while panning and zooming in real time.
The ER Mapper wavelet based compression technology results in manageable file sizes without a significant loss of image quality (Earth Resource Mapping Pty Ltd, 2001). ER Mapper Compressed Wavelet (ECW) v2.0 compression at a 9:1 ratio is at a low enough compression ratio where the “lost” data usually is not visually noticeable. Although keep in mind that visually lossless compression is not a mathematical guarantee but a subjective term.
For more information on ER Mapper Compressed Wavelet (ECW) compression, please refer tothis publication:
Earth Resource Mapping Pty Ltd. Using and distributing ECW V2.0 wavelet compressed imagery. Technical white paper. 2001.
<http://www.earthetc.com/iws/Downloads/tech_papers/ecwv20wp.pdf>
To learn more about the 2005 half-meter DOQs, please contact the Oregon Geospatial Enterprise Office:
Cy Smith (cy.smith@state.or.us) at 503-378-6066 or write to:
Oregon Geospatial Enterprise Office (GEO)
955 Center St. NE Room 470
Salem, OR 97301
http://gis.oregon.gov/DAS/EISPD/GEO/
You may also find information at the Oregon Geospatial Enterprise Office (GEO) Oregon Orthoimagery Framework Group Web page: http://gis.oregon.gov/DAS/EISPD/GEO/fit/orthoimagery/OrthoFrame.shtml.
