What are the formats for digital raster graphics (DRGs)?
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Question:
What are the formats for digital raster graphics (DRGs)?
Answer:
The file format is called Tagged Image Format Files (TIFF). DRGs are packbit compressed. Each has been color standardized to 13 colors. DRGs are georeferenced to the 16 2.5-minute ticks. DRGs are cast on a UTM projection. The original horizontal datum (NAD 83, NAD 27) is preserved in the projection parameters (Hawaiian quadrangles present a certain problem. The old Hawaiian datum is not preserved; use a mean Hawaiian datum with a Clarke 1866 spheroid).
Even though DRGs only have 13 colors, the data are output with 8 bits per pixel. This decision was made because of the belief that more software would be able to read 8-bit data than other formats.
