READMEDOQ.htm

This file contains descriptions for each item in the doqindex.dbf file. These items were extracted from the DOQ header data and MrSID processing output for each DOQ. Items included here are unique to each DOQ and do not include additional information pertinent to all DOQs, which is included in the FGDC-compliant metadata file (such as the projection, which is UTM).

This file was last modified 5/2/2000 by C.S. McGarry.

USGSNAME

Codified USGS name. Files are stored with the USGS file naming conventions. The USGS subdivides data by 1 x 1 degree tile based on the coordinates of the southeast corner. Each 1 x 1 degree tile contains:

• one-half of a 1 x 2 degree quadrangle
• two 30 x 60 minute quadrangles
• 64 7.5' quadrangles in an 8 x 8 grid
• 256 quarter-quadrangles (scale of DOQ imagery)

There are 27 1 x 1 degree tiles that intersect Illinois.

Here is the general form for path and filename:

<1 x 1 degree tile><quad designation><quadrant>

Where

• <tile_num> is the 1 x 1 degree tile number, composed of latitude and longitude values
• <quad designation> is the 7.5-minute quadrangle designation based on the 8 x 8 grid
• <quadrant> is the quarter-quad value (1-4, clockwise from the northwest quadrant).

For example, the southwest quadrant of the Urbana, IL quadrangle is 40088A24, where 40 is the tile latitude, 088 is the tile longitude, A2 is the quadrangle location in the tile, and 4 is the southwest quadrant of the quadrangle. Names are independent of file format. This nomenclature is applicable to the original

DOQ files (GeoTIFF) or the MrSID compressed files (SID).

QUADNAME

The USGS name of the quadrangle (non-codified, alphabetic name, ie. Urbana, IL)

QUADRANT

The quarter-quad direction (non-codified, alphabetic name, i.e. NW/NE/SE/SW)

UTM_ZONE

The UTM zone of the DOQ (either 15 or 16 in Illinois)

COLUMNS

Number of pixel columns ("samples") in the original GeoTIFF image

ROWS

Number of pixel rows ("lines") in the original GeoTIFF image

RMSE_XY

Root Mean Square Error in the imagery (measured in meters)

SRCIMG_ID

Unique source image identification number for original photography

SRCIMG_D

Date of original photography (yyyymmdd)

SRCDEM_D

Date of DEM data used for orthorectification (yyyymmdd)

ORIG_SIZE

Size of the original GeoTIFF image, as delivered from the USGS (in megabytes)

COMP_SIZE

Size of the compressed MrSID .sid image, as modified by the ISGS (in megabytes)

RATIO

Actual compression ratio. A target ratio of 15.0:1 was used on all imagery, but the actual compression ratio varies between images.

DOQ_DATE

Date of production of original GeoTIFF imagery at USGS (yyyymmdd)

SID_DATE

Date of production of the compressed MrSID imagery at ISGS (yyyymmdd)

SID_TIME

Time of production of the compressed MrSID imagery at ISGS (hh:mm:ss) Image boundary coordinates are taken from the tic marks placed in the image. The actual image extends approximately 300 meters beyond the boundary of the tic marks so that image mosaicking can be smoother. Primary tics (NAD83) are solid "+" symbols and secondary tics (NAD27) are dashed "+" symbols very near the primary tics.

W_LONG

West longitude of bounding quarter-quadrangle

E_LONG

East longitude of bounding quarter-quadrangle

N_LAT

North latitude of bounding quarter-quadrangle

S_LAT

South latitude of bounding quarter-quadrangle

ORIGIN_X

x-coordinate of the imagery origin

ORIGIN_Y

y-coordinate of the imagery origin

SORIGIN_X

x-coordinate of the imagery secondary origin

SORIGIN_Y

y-coordinate of the imagery secondary origin

NW_X

x-coordinate of the northwest quarter quadrangle corner (solid +)

NW_Y

y-coordinate of the northwest quarter quadrangle corner (solid +)

NE_X

x-coordinate of the northeast quarter quadrangle corner (solid +)

NE_Y

y-coordinate of the northeast quarter quadrangle corner (solid +)

SE_X

x-coordinate of the southeast quarter quadrangle corner (solid +)

SE_Y

y-coordinate of the southeast quarter quadrangle corner (solid +)

SW_X

x-coordinate of the southwest quarter quadrangle corner (solid +)

SW_Y

y-coordinate of the southwest quarter quadrangle corner (solid +)

S_NW_X

x-coordinate of the northwest quarter quadrangle secondary corner (dashed +)

S_NW_Y

y-coordinate of the northwest quarter quadrangle secondary corner (dashed +)

S_NE_X

x-coordinate of the northeast quarter quadrangle secondary corner (dashed +)

S_NE_Y

y-coordinate of the northeast quarter quadrangle secondary corner (dashed +)

S_SE_X

x-coordinate of the southeast quarter quadrangle secondary corner (dashed +)

S_SE_Y

y-coordinate of the southeast quarter quadrangle secondary corner (dashed +)

S_SW_X

x-coordinate of the southwest quarter quadrangle secondary corner (dashed +)

S_SW_Y

y-coordinate of the southwest quarter quadrangle secondary corner (dashed +)