USGS, 19971029, Goldfield: USGS, Reston, VA.
This is a Raster data set. It contains the following raster data types:
4.1.2.1.2.2 LONGITUDE AT CENTRAL MERIDIAN: -117.000
Planar coordinates are encoded using row and column
Abscissae (x-coordinates) are specified to the nearest 10.160000
Ordinates (y-coordinates) are specified to the nearest -10.160000
Planar coordinates are specified in "meters"
The horizontal datum used is North American Datum 1927.
The ellipsoid used is Clarke 1866.
The semi-major axis of the ellipsoid used is 6378206.4.
The flattening of the ellipsoid used is 1/294.98.
This DRG was produced through an Innovative Partnership agreement between The Land Information Technology Company, Ltd., of Aurora, CO and the USGS.
A DRG is useful as a source or background layer in a GIS, as a means to perform quality assurance on other digital products, and as a source for the collection and revision of DLG data. DRG's can also be merged with other digital data, e.g. DEM's or DOQ's, to produce a hybrid digital file.
1. Production of a DRG begins with the scanning of a paper 7.5-minute topographic map (map1) on a high-resolution scanner. Scanning resolutions range from 500 - 1000 dpi with the output file running between 160-300 mb.
2. Removal of screens (descreening) and color quantization to reduce the number of colors also takes place during the scanning phase.
3. The raw scan file is then transformed and georeferenced using UTM coordinates of the sixteen 2.5-minute grid ticks, which are obtained using the in-house produced program COORDAT and stored in a ground control file. Those sixteen 2.5-minute ticks are interactively visited and assigned their respective UTM coordinates. USGS program XSHAPES4 then performs a piecewise linear rubber sheet transformation.
4. An output resolution of 2.4 meters (8.2 feet) is chosen in order to resample the file to 250 dpi.
5. The image file is converted to a TIFF and further reduced by converting the file to a run length encoding Packbits compression(type 32773).
6. The color palette of the compressed DRG is then standardized by replacing the original RGB values assigned during the scanning process with standard RGB value combinations using the in-house produced TIFFREMAP program.
7. Prior to archiving the DRG undergoes the following quality assurance procedures:
a. The color index values of each DRG are checked to ensure the RGB combinations are consistent with the standardized color palette.
b. All DRG files are inspected to ensure that they are geometrically consistent with normal map presentation.
c. Selected DRG's are checked to ensure that data elements in the DRG metadata file correspond to the map collar information and to the information in the associated image file.
d. Selected DRG's are checked for georeferencing accuracy by comparing the book value of latitude and longitude tick marks with corresponding tick intersections in the DRG image.
e. Transformations are checked on selected DRG's by comparing the positions of well defined points, such as UTM grid intersections in the graphic product, with the corresponding image points in the DRG.
USGS DRG production specifications are available on request from the National Mapping Division and Mid-Continent Mapping Center by contacting:
Rolla-ESIC U.S. Geological Survey 1400 Independence Rd., MS231 Rolla, MO 65401-2602 Phone (573)308-3500 Facsimile (573)308-3615 E-mail to mcmcesic@usgs.gov World Wide Web: <http://mcmcweb.er.usgs.gov/drg/>
Data sources used in this process:
The DRG is an 8-bit color image that employs a color palette to ensure uniform colors throughout a particular DRG series. All DRG's within a series must have the same RGB value.
While the datum of the published map is retained to be consistent with other USGS digital data, this image is cast on the UTM and may be INCONSISTENT with the credit note on the image collar.
Refer to the DRG collar for information about vertical positional accuracy.
The DRG is a faithfully reproduced digital image of the original source map. Some differences may be detected between the source graphic used and the DRG due to the RGB values assigned that particular color. The intent is to recreate those colors as near as possible. Data completeness for DRG files reflect content of the source graphic. Features may have been eliminated or generalized on the source graphic due to scale and legibility constraints. For information on collection and inclusion criteria, see U.S. Geological Survey, 1994, Standards for 1:24,000-Scale Digital Line Graphs and Quadrangle Maps: National Mapping Program Technical Instructions and U.S. Geological Survey, 1994, Standards for Digital Line Graphs: National Mapping Program Technical Instructions.
Not Applicable
Are there legal restrictions on access or use of the data?
- Access_Constraints: "None"
- Use_Constraints:
- Acknowledgment of the USGS would be appreciated in products derived from these data.
Earth Science Information Center, U.S.
507 National Center
Reston, Virginia 22092
1 800 USA MAPS (voice)
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. The USGS will warrant the delivery of this product in computer-readable format and will offer appropriate adjustment of credit when the product is determined unreadable by correctly adjusted computer input peripherals, or when the physical medium is delivered in damaged condition. Requests for adjustment of credit must be made within 90 days from the date of this shipment from the ordering site.
| Data format: | TIFF (version 6.0) |
|---|---|
| Media you can order: |
"CD-ROM"
(format "ISO 9660"; DRG image files with corresponding metadata files. )
|
U.S. Geological Survey
590 National Center
Reston, Virginia 22092
1 703 648 4533 (voice)
Copies of this publication are