Isolate the data portion of a USGS DRG (i.e., remove collar information)

Summary

United States Geological Survey digital raster graphics (DRGs) are often provided with their collars intact. It may be desirable to remove this part of the images, particularly where several DRGs are to be tiled together.

Procedure

1. Uncompress the DRG file after it is downloaded.
2. Check and see if there is a .fgd file in the data directory. This file contains background information on the DRG, such as projection and the data extents inside the collar.
3. Determine the lower left, upper left, upper right, and lower right coordinates of the data either from the .fgd file or from the image itself (look at the corners). Make a text file with these coordinates.
   
   For example, the .frg file contains the following information in the Spatial Domain section:
   
   

    Bounding Coordinates  
   
     1.5.1.1  WEST BOUNDING COORDINATE:  -88.375000
     1.5.1.2  EAST BOUNDING COORDINATE:  -88.250000  
     1.5.1.3  NORTH BOUNDING COORDINATE:  41.750000 
     1.5.1.4  SOUTH BOUNDING COORDINATE:  41.625000 
   
     Make a text file called COORD.TXT with the values as follows
     (West South, West North, East North, East South):
   
     -88.375000 41.625000
     -88.375000 41.750000
     -88.250000 41.750000
     -88.250000 41.625000

   
   
4. These coordinates need to be converted to Universal Transverse Mercator (UTM) to align over the data. The UTM zone the data is located in can be determined from the .fgd file.
   
   For example, this information is in the .fgd file in the Spatial Reference Information section:
   
   

     4.1.2.2.2.1   UTM ZONE NUMBER:  16

   
   
5. Make a projection file called GEOG2UTM.PRJ to use when converting the decimal degree units of the data area coordinates to UTM.
   
   

     input 
     projection geographic
     units dd
     datum nad27
     parameters
     output
     projection utm
     units meters
     zone 16
     datum nad27
     parameters 
     end 

   
   
6. Project the geographic coordinates to UTM.
   
   

   Code:
   Usage: PROJECT <COVER | FILE> <input> <output> {projection_file}
   Arc: project file coord.txt output.txt geog2utm.prj

   
   
   

   The contents of OUTPUT.TXT should be something like this: 
   
            385455.1963        4608841.8819
            385676.7404        4622719.9991
            396069.9634        4622561.4366
            395868.5676        4608683.4007

   
   
7. Use these coordinates to create a generate file called MAKEPOLY.GEN that will be used to generate a polygon. The first line will be the polygon ID; its coordinates should fall within the range of the extremes.
   
   

    101,390000.0000,4615000.0000        
    385455.1963,4608841.8819
    385676.7404,4622719.9991
    396069.9634,4622561.4366
    395868.5676,4608683.4007
    385455.1963,4608841.8819
    end
    end

   
   
8. Generate the polygon coverage.
   
   

   Code:
   Arc: GENERATE clipbox
   generate: INPUT makepoly.gen
   generate: POLYGONS
   generate: QUIT
   
   Arc: CLEAN clipbox clipboxcln

   
   
9. This polygon can be used to clip the image, but it will clip out based on the bounding box, not the actual arc. This would result in slivers of collar data appearing at the corners of the clipped image. (The command would be Arc: rectify drg.tif drgclip.tif # # clipbox.)
   Therefore, the image must be converted to a grid for further processing.
   
   

   Code:
   Arc: IMAGEGRID drg.tif drggrid

   
   
10. Clip the data area out using the clip coverage.
    
    

    Code:
    Grid: gridclip drggrid drgclip cover clipboxcln

    
    
11. To preserve the colors of the DRG in the grid, a colormap file must be made. The color definitions are located in the .fgd file.
    
    

                           USGS DRG Color Palette
          
           Digital Number    Color       Red      Green    Blue 
           
                 0           Black       0        0        0
                 1           White       255      255      255 
                 2           Blue        0        151      164 
                 3           Red         203      0        23 
                 4           Brown       131      66       37  
                 5           Green       201      234      157 
                 6           Purple      137      51       128 
                 7           Yellow      255      234      0 
                 8        Light Blue     167      226      226 
                 9        Light Red      255      184      184 
                 10       Light Purple   218      179      214 
                 11       Light Grey     209      209      209
                 12       Light Brown    207      164      142
    
      Make a colormap file from the information above in the following format:
    
       "drgpalette.clr"
      0 0 0 0 (Black)
      1 255 255 255 (White)
      2 0 151 164 (Blue)
      3 203 0 23 (Red)
      4 131 66 37 (Brown)
      5 201 234 157 (Green)
      6 137 51 128 (Purple)
      7 255 234 0 (Yellow)
      8 167 226 226 (Light Blue)
      9 255 184 184 (Light Red)
      10 218 179 214 (Light Purple)
      11 209 209 209 (Light Grey)
      12 207 164 142 (Light Brown)
    
      Note: This palette could also be made into a shadeset.

    
    
12. The data area can be displayed as follows:
    
    

    Code:
    Grid: gridpaint drgclip # # # drgpalette.clr 

    
    
13. To create a TIFF file from the grid, use the GRIDIMAGE command with the colormap file.
    
    

    Code:
    Arc: gridimage drgclip drg.clr drgcli.tif tiff compress