|Originator||U.S. Geological Survey and Digital Aerial Solutions, LLC|
|Title||USGS High Resolution Orthoimagery, Minneapolis-St. Paul, Minnesota, Spring 2012|
|Abstract||This dataset consists of 0.3-meter pixel resolution (approximately 1-foot), natural color orthoimages covering the Minneapolis-St. Paul urban area footprint, an area of 1,583 square miles.
An orthoimage is remotely sensed image data in which displacement of features in the image caused by terrain relief and sensor orientation have been mathematically removed. Orthoimagery combines the image characteristics of a photograph with the geometric qualities of a map.
[Note: this metadata record was reformatted at the Minnesota Geospatial Information Office from the record provided by USGS - several of the fields were changed to reflect MnGeo's seamless WMS data delivery]
|Purpose||The data depicts geographic features on the surface of the earth. It was created to provide easily accessible geospatial data which is readily available to enhance the capability of Federal, State, and local emergency responders, as well as plan for homeland security efforts. This data also supports The National Map.
A digital orthoimage is a geometrically accurate photographic record of landscape conditions at the time of the corresponding aerial photography. As such, High Resolution Orthoimagery is useful for a variety of applications, such as environmental monitoring, facility engineering/maintenance, city/county planning, property line review, etc. The digital orthoimage can be used alone or as a raster basemap for corresponding vector line mapping. The detailed focus of High Resolution Orthoimagery provides emergency responders critical information in determining the best evacuation routes, alternative routes and safe access to aid. High Resolution Orthoimagery assists law enforcement personnel in determining the best locations to place surveillance cameras in high-traffic urban areas and popular attractions. The data assists Federal, State and local emergency responders in planning for homeland security efforts. This data also supports The USGS Seamless system.
|Time Period of Content Date||03/2012|
|Currentness Reference||Imagery was flown March 25 and 29 and April 3 and 4, 2012.|
|Maintenance and Update Frequency||Irregular|
|Spatial Extent of Data||Minneapolis and St. Paul, Minnesota (Twin Cities metropolitan area)|
|Place Keywords||Twin Cities metropolitan area, Minneapolis, St. Paul, Saint Paul, MN, Minnesota|
|Theme Keywords||imageryBaseMapsEarthCover, orthophoto, air photo, aerial photo, aerial photography, image map|
|Theme Keyword Thesaurus||ISO 19115 Category|
|Access Constraints||Any downloading and use of these data signifies a user's agreement to comprehension and compliance of the USGS Standard Disclaimer. Insure all portions of metadata are read and clearly understood before using these data in order to protect both user and USGS interests.|
|Use Constraints||None. 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. Acknowledgment of the U.S. Geological Survey would be appreciated for products derived from these data. There is no guarantee of warranty concerning the accuracy of the data. Any user who modifies the data is obligated to describe the types of modifications they perform. User specifically agrees not to misrepresent the data, nor to imply that changes made were approved or endorsed by the U.S. Geological Survey. Please refer to www.usgs.gov/privacy.html for the USGS disclaimer.|
|Contact Person Information||,
Customer Services Representative|
U.S. Geological Survey
USGS Earth Resources Observation and Science Center
Sioux Falls, SD 57198-0001
|Browse Graphic||Click to view a data sample|
|Associated Data Sets||For information on other air photos available for Minnesota, see www.mngeo.state.mn.us/chouse/airphoto/index.html|
|Section 2||Data Quality|
|Attribute Accuracy||Radiometry is verified by visual inspection of the digital orthophoto. Slight systematic radiometric differences may exist between adjacent orthoimage files; these are due primarily to differences in source image capture dates and sun angles along flight lines. These differences can be observed in an image's general lightness or darkness when it is compared to adjacent orthoimage file coverages. Tonal balancing may be performed over a group of images during the mosaicking process which may serve to lighten or darken adjacent images for better color tone matching.|
|Logical Consistency||All GeoTIFF tagged data and image file sizes are validated using commercial GIS software to ensure proper loading before being archived. This validation procedure ensures correct physical format and field values for tagged elements. Seamlines and tile edges are visually inspected. Seamlines mismatches are not corrected unless the overall displacement exceeds one meter. Logical consistency is implicit in the raster image data structure. Source imagery is cloud free.|
|Completeness||Orthoimages are visually inspected for completeness to ensure that no gaps or image misplacements exist within and between adjacent images. These images are derived by mosaicking multiple images to ensure complete coverage. Source imagery is cloud free. Photography was flown during leaf-off in deciduous vegetation regions. Coastal areas and international boundary regions may have areas without images (void areas) in parts of the coverage. These void areas have a radiometric value of either zero (black) or 128 (uniform gray).|
|Horizontal Positional Accuracy||The design accuracy is estimated not to exceed 3-meters NSSDA 95% confidence (0.88-meters Root Mean Squared (RMSE) Error XY (0.62 meter RMSE X or Y).
The estimated horizontal positional accuracy value for the dataset is 0.52 meters.
The horizontal positional accuracy and the assurance of that accuracy depend, in part, on the accuracy of the data inputs to the rectification process. The location of existing USGS photoidentifiable ground control and contractor aerotriangulation points were evaluated on the Geotiff image and compared with their ground values in order to determine an overall accuracy for each test block of orthoimages within the project. After image coordinate measurement was completed for each block, an RMSE for the diagonal error was calculated for the orthoimages within the block. This value is an estimate of the horizontal accuracy of the tile expressed in meters.
The relative accuracy is assembled by comparing rectified images generated from adjacent strips of imagery. The absolute accuracy is assessed by measuring the ground control points in the rectified image against the actual surveyed co-ordinate position. The testing is for overall accuracy. This data has been produced to be fully compliant with the National Map Accuracy Standards (NMAS) for mapping at this scale.
Citation: Federal Geographic Data Committee, 1998, Geospatial Positioning Accuracy Standard, Part 3, National Standard for Spatial Data Accuracy, FGDC-STD-007.3-1998
|Vertical Positional Accuracy||There is no vertical accuracy component to orthophotography.|
1. Source Imagery - ADS40, Originator: Digital Aerial Solutions, LLC
(Sensor Head 52) Digital Camera Imagery Control - Airborne GPS/IMU supplemented with photo identifiable field control Aerotriangulation, Orthorectification - SOCET SET, ORIMA Elevation Model - USGS DEM Mosaic - OrthoVista
The digital imagery mission was composed of a total of 4 lifts. Imagery (1-ft, 0.3 meter GSD) was obtained at an altitude of 9,450 feet above ground level on 25 and 29 Mar and 3 and 4 Apr 2012. The missions were flown with a Leica ADS40 (Sensor Head 52) digital camera with ABGPS and IMU. This imagery provides the data for the digital orthoimage. Imagery was acquired on the following dates - Lift Date 0103252012 25 Mar 2012 0203292012 29 Mar 2012 0304032012 03 Apr 2012 0404042012 04 Apr 2012
2. GPS Ground Control
Horizontal and vertical control was used to establish positions and elevations for reference and correlation purposes and as input to the aerotriangulation process. Control consists of photoidentifiable surveyed ground control for ground reference. A total of 20 photoidentifiable ground control points were collected.
3. Minneapolis-St. Paul, MN 10-Meter USGS DEM
USGS format elevation data with a 10-meter grid post interval and covering a 7.5-minute x 7.5-minute quadrangle in extent. Used to provide ground elevations for orthorectification process.
4. Airborne GPS/IMU Data, Originator: Digital Aerial Solutions, LLC
Airborne GPS (ABGPS) and IMU data are collected with an onboard dual frequency GPS survey unit and a corresponding IMU system in combination with the digital imagery. The GPS data provides the position of the imagery at the time of capture while the IMU system records instantaneous changes in position and attitude of the sensor. The GPS/IMU, base station, and ground control processing are an important step towards the development of accurate orthoimages.
PROCESSING STEPS at Digital Aerial Solutions, LLC
The following describes the digital production sequence.
1. The raw ADS40 (Level-0) data and associated GPS and IMU data for each mission is downloaded from the hard drives and checked to confirm that no files have been corrupted and that all data can be successfully downloaded.
2. The GPS and IMU data are post-processed along with the base station data to produce a precise position and attitude stream for each line of imagery. Post processing uses the high frequency readouts of the IMU to verify the GPS data and to provide instantaneous positioning of each line of imagery between GPS recordings. Likewise, the IMU attitude data is corrected for bias/drift and transformed to real world coordinates by using the GPS data. This process creates Level-1 rectified imagery which is an approximately geo-positioned image.
3. The ADS40 production process uses aerial triangulation techniques to combine the short-term accuracy of the IMU with high global accuracy of GPS. In combination with the minimum required number of ground control points (GCPs), aerial triangulation delivers best fitting results on the ground. The extra information added to the system by automatic tie point measurements (APM) leads to very reliable orientation results where photogrammetric measurements serve to control IMU/GPS measurements and vice versa.
4. The results of the APM are run through a combined bundle adjustment process to further refine the measured image coordinates and the position and attitude values from IMU and GPS computed by IMU/GPS post processing. The bundle adjustment process equally compensates for systematic errors such as the misalignment between IMU and sensor axes, IMU/GPS drift, and the datum difference between IMU/GPS and ground control coordinate system. This results in a very accurate and precise determination of the parameters of exterior orientation which are later used for Orthorectification.
5. The orthorectification process uses the raw Level-0 data as the input imagery source to avoid repeated re-sampling of the imagery to yield the best possible image quality and accuracy. The raw Level-0 true color imagery is orthorectified to the DEM using the adjusted position and orientation results from the aerial triangulation phase. The orthorectified strip of imagery is called the Level-2 data.
6. The resulting images are then mosaicked and color balanced.
7. The final 1500-meter by 1500-meter tiles are clipped out and the imagery is output in uncompressed GeoTIFF format with no overlap.
8. The completed natural color digital orthophotos are checked for image quality. Minor artifacts are corrected using Adobe Photoshop in an interactive editing session. Digital tiles are assigned final names based on the U.S. National Grid.
PROCESSING STEPS at EROS Data Center, USGS
Data received at EROS were verified as: Projection: NAD_1983_UTM_Zone_15N Resolution: 0.3000 m Type: Natural Color and resampled to align to the USNG using the USGS Seamless system. The naming convention is based on the U.S. National Grid (USNG), taking the coordinates of the SW corner of the orthoimage. The metadata were imported and updated for display through The National Map Server.
PROCESSING STEPS at MnGeo
USGS delivered the imagery to MnGeo in TIFF format in tiles with no overlap. MnGeo read them directly into a database and serves the images over the web via a WMS server in JPG format.
|Section 3||Spatial Data Organization (not used in this metadata)|
|Section 4||Coordinate System|
|Horizontal Coordinate Scheme||Universal Transverse Mercator|
|UTM Zone Number||15|
|Overview||Natural color orthoimagery is organized in three color bands or channels which represent the red, green, and blue portions of the spectrum. Each image pixel is assigned a triplet of numeric values, one for each color band. Numeric values range from 0 to 255. Areas where data is incomplete due to lack of full image coverage are represented with the numeric value of 0.|
|Detailed Citation||U.S. Department of the Interior, U.S. Geological Survey, 1999, Standards for Digital Orthoimagery: Reston, VA|
|Publisher||USGS and MnGeo|
|Contact Person Information||Nancy Rader,
GIS Data Coordinator|
Minnesota Geospatial Information Office
658 Cedar Street
St. Paul, MN 55155
|Distributor's Data Set Identifier||Twin Cities high resolution DOQs 2012|
|Distribution Liability||1. USGS Disclaimer:
Although these data have been processed successfully on a computer system at the USGS, no warranty expressed or implied is made by the USGS regarding the use of the data on any other system, nor does the act of distribution constitute any such warranty. Data may have been compiled from various outside sources. Spatial information may not meet National Map Accuracy Standards. This information may be updated without notification. The USGS shall not be liable for any activity involving these data, installation, fitness of the data for a particular purpose, its use, or analyses results.
2. MnGeo disclaimer: www.mngeo.state.mn.us/chouse/disclaimer.html
|Ordering Instructions||The imagery is available to view via WMS (Web Mapping Service) from either of two locations:
1. MnGeo's Geospatial Image Server
Click on 'Online Linkage' field below to see a webpage that provides the url to connect to the Geospatial Image Server as well as information about how to use WMS services.
2. USGS National Map Viewer and Download Platform:
The National Map interface allows for data downloads within a customer defined area of interest. Zoom tools are available that can be used to investigate areas of interest on the map interface. The download tool allows the customer to capture layers from the map. A request summary page is then generated with the download layers listed. By clicking the "download" button on the summary page, a zipped file will be generated that can be saved on the customer's computer. The file can then be unzipped and imported into various user software applications
|Online Linkage||I AGREE to the notice in "Distribution Liability" above. Clicking to agree will either begin the download process or link to download information. See "Ordering Instructions" above for details.|
|Section 7||Metadata Reference|
|Contact Person Information||Nancy Rader,
GIS Data Coordinator|
Minnesota Geospatial Information Office
658 Cedar Street
St. Paul, MN 55155
|Metadata Standard Name||Minnesota Geographic Metadata Guidelines|
|Metadata Standard Version||1.2|
|Metadata Standard Online Linkage||http://www.mngeo.state.mn.us/committee/standards/mgmg/metadata.htm|