Metadata for 2006 Color Orthophotographs of Helena, Montana

Identification Information
Data Quality Information
Spatial Data Organization Information
Spatial Reference Information
Distribution Information
Metadata Reference Information

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Identification Information:

Citation:

Originator: City of Helena
Originator: Infotech Enterprises America (formerly VARGIS, LLC)
Publication date: 06/12/2007
Title: 2006 Color Orthophotographs of Helena, Montana
Online linkage: http://apps.msl.mt.gov/Geographic_Information/Data/Aerial_Photos/helena_hrcolor_2006.aspx

Abstract:

Color orthophotographs of the City of Helena, photogrammetrically compiled from aerial photography flown in April 20, 2006.

Purpose:

Digital Orthophotographs serve a variety of purposes, from interim maps to field references for earth science investigations and analysis. The orthophotograph is useful as a layer of a geographic information system and as a tool for revising digital line graphs and topographic maps. City of Helena intends to utilize the orthophotographs to support their current planning and future development needs.

Supplemental information:

The project encompasses approximately 44 squares miles of the urban area in and around the City of Helena. The scale of the aerial photography negative was 1"=660' exposed at a flight height of 3,500 feet above mean ground level. The resolution for this orthophotograph is 0.0150 meter, or approximately 6 inches.

Time period of content:

Calendar date: 04/20/2006
Currentness reference: ground condition

Status:

Progress: Complete
Maintenance and update frequency: As needed

Access constraints: None

Use constraints:

The Montana State Library provides this product/service for informational purposes only. The Library did not produce it for, nor is it suitable for legal, engineering, or surveying purposes. Consumers of this information should review or consult the primary data and information sources to ascertain the viability of the information for their purposes. The Library provides these data in good faith but does not represent or warrant its accuracy, adequacy, or completeness. In no event shall the Library be liable for any incorrect results or analysis; any direct, indirect, special, or consequential damages to any party; or any lost profits arising out of or in connection with the use or the inability to use the data or the services provided. The Library makes these data and services available as a convenience to the public, and for no other purpose. The Library reserves the right to change or revise published data and/or services at any time.

Point of contact:

City of Helena
316 N. Park Ave.
Helena, Montana 59624
Telephone: 406-447-8389
E-Mail: espangenberg@co.lewis-clark.mt.us

Data Quality Information:

Attribute accuracy report:

During photographic reproduction of the source photographs, limited analog dodging is performed to improve image quality. Analog dodging consists of holding back light from certain areas of the sensitized photographic material to avoid overexposure. The diapositive is inspected to ensure clarity and radiometric uniformity. Diapositive image brightness values are collected with a minimum of image quality manipulation. Image brightness values may deviate from the brightness values of the original images because of image value interpolation during the scanning and rectification processes. Radiometry is verified by visual inspection of the digitalorthophoto quadrangle with the original unrectified image to determine if the digital orthophoto has the same or better image quality as the original unrectified input image. Slight systematic radiometric differences can be detected between adjacent DO files; these are due primarily to differences in source photograph capture dates and sun angles along flight lines when the aerial photographs were taken. These differences can be observed in an image's general lightness or darkness when it is compared to adjacent DO file coverages.

Logical consistency report:

All Digital Orthophotograph (DO) header data and image file sizes are validated using USGS software before being archived. This validation procedure ensures correct physical format and field values for header elements. Logical relationships between header elements are tested.

Completeness report:

DO images are visually inspected for completeness to ensure that no gaps or image misplacements exist. DO's are cloud free within the image area. Some clouds may, very infrequently, appear in the overedge coverage.

Horizontal Positional Accuracy Report:

The City of Helena area horizontal positional accuracy and the assurance of that accuracy depend, in part, on the accuracy of the data inputs to the rectification process. These inputs consist of the digital elevation model (DEM),aerotriangulation control and methods, the photo source camera calibration, scanner calibration, and aerial photographs that meet National Aerial Photography Program (NAPP) standards.

Vertical positional accuracy report:

The vertical accuracy of the verified DEM is equivalent to or better than 1" = 100', with a root mean square error (RMSE) of no greater than 1/10000 of the flying heigth. Field control is acquired by second order class 1 or better survey methods sufficiently spaced to meet National Map Accuracy Staandards (NMAS) for 1:1,000-scale products.

Lineage:

Process step:: The production procedures, instrumentation, hardware and software described here are specific to the production of the City of Helena area referenced in this document. The rectification process requires, as input, a user parameter file to control the rectification process, a digital elevation model (DEM) gridded to user specified bounds, projection, zone, datum and X-Y units, a scanned digital image file (PHOTO) covering the same area as the DEM, ground X-Y-Z point values (CONTROL) and their conjugate photo coordinates in the camera coordinate system, and measurements of the fiducial marks (CAMERA) in the digitized image.

The camera calibration report (CAMERA) provides the focal length of the camera and the distances in millimeters from the camera's optical enter to the camera's 8 fiducial marks. These marks define the frame of reference for spatial measurements made from the photograph.

Ground control points (CONTROL) supplemented with ABGPS and developed in a triangulation, are second order class 1, and meet National Map Accuracy Standard (NMAS) for 1:1,000-scale. Ground control points are in the City of Helena specified projection / datum / unit of measure. Horizontal and vertical residuals of aerotriangulated tie-points are equal or less than 1/10000 of the flying height.

Standard aerotriangulation passpoint configuration consists of 32 ground control points, one near each corner, one at the center near each side and 1 near the center of the photograph, are used. The conjugate positions of the ground control points on the photograph are measured and recorded in camera coordinates.

The raster image file (PHOTO) is created by scanning an aerial photograph film diapositive with a precision image scanner (ZEISS scanner). An aperture of 14 microns is used. The elevation data source (DEM) is derived from the photography (PHOTO) using softcopy stereoplotter workstations. All DEM data is equivalent to or better than 1" = 100'.

A DEM covering the extent of the photograph is used for the rectification. The DEM is traversed from user-selected minimum to maximum X-Y values add the DEM X-Y-Z values are used to find pixel coordinates in the digitized photograph using transformations mentioned above. For each raster image cell subdivision, a brightness value is obtained using nearest neighbor, bilinear, or cubic convolution resampling of the scanned image. The pixel processing algorithm is indicated in the header file. An inverse transformation relates the image coordinates referenced to the fiducial coordinate space back to scanner coordinate space.

Rectification Process:
The photo control points and focal length are interactively fitted to their conjugate ground control points using a single photo space resection equation using Instantaneous Simultaneous Bundle Block Adjustment (ISBBA). From this mathematical fit is obtained a rotation matrix of constants about the three axes of the camera. This rotation matrix can then be used to find the photograph or camera coordinates of any other ground X-Y-Z point. Next a two dimensional fit is made between the measured fiducial marks on the digitized photograph and their conjugate camera coordinates. Transformation constants are developed from the fit and the camera or photo coordinates are used in reverse to find their conjugate pixel coordinates on the digitized photograph.

Quality Control:
All data is inspected according to a quality control plan submitted by Infotech Enterprises America; formerly VARGIS, LLC and approved.

Spatial Data Organization Information:

Raster object information:

Raster object type: Pixel
Row count: 77827
Column count: 76680
Vertical count: 1

Spatial Reference Information:

Horizontal coordinate system definition:

Grid coordinate system name: State Plane Coordinate System

SPCS zone identifier: 2500

Lambert conformal conic:

Standard parallel: 45.000000
Standard parallel: 49.000000
Longitude of central meridian: -109.500000
Latitude of projection origin: 44.250000
False easting: 600000.000000
False northing: 0.000000

Planar distance units: meters

Geodetic model:

Horizontal datum name: D_North_American_1983_HARN
Ellipsoid name: Geodetic Reference System 80
Semi-major axis: 6378137.000000
Denominator of flattening ratio: 298.257222

Distribution Information:

Distributor:

Montana State Library
PO Box 201800
Helena, MT 59620-1800
Telephone: 406-444-5354
TDD/TTY telephone: 406-444-4799
Fax: 406-444-0266
E-Mail: geoinfo@mt.gov

Resource description: Downloadable Data

Distribution liability:

Standard order process:

Digital form:

Format name: MrSID
Online option:

Metadata Reference Information:

Metadata date: 01/06/2014

Metadata review date: 07/19/2013

Metadata review date: 04/17/2013

Metadata review date: 06/11/2007

Metadata contact:

City of Helena
316 N. Park Ave.
Helena, Montana 59624
Telephone: 406-447-8389
E-Mail: espangenberg@co.lewis-clark.mt.us