This system provides the 24k Quarter-Quad code as per the system used by the Center for
Lidar Information Coordination and Knowledge (http://lidarbb.cr.usgs.gov). The latitude and
longitude values should be the southeast corner of the tile. Quarter-Quads are each 1/16 of
a degree in width and height. They are referenced on the NAD83 Datum.
These codes have the following structure:
AAOOOaoq
Where
AA is the positive whole number component of the latitude.
OOO is the positive whole number component of the longitude (zero-padded to a width
of 3).
a is an alpha character a-h designating which quad in the degree of latitude, where a is
closest to 0 minutes and h is closest to the next full degree. Each represents 1/8 of a
degree.
o is a numeral 1-8 designating which quad in the degree of longitude, where 1 is
closest to 0 minutes and 8 is closest to the next full degree. Each represents 1/8 of a
degree.
q is an alpha character a-d designating which quarter in the quad, where a is
southeast, b is northeast, c is northwest, and d is southwest. Each Quarter-Quad is 1/16 of
a degree in latitude and 1/16 of a degree in longitude.
For example, 47104h2c means:
47 - 47 degrees latitude
104 - 104 degrees longitude
The section is in the degree range starting 47¡N, 104¡W.
h - h is the 8th in sequence, so it is the last section and would start at 7/8 of a degree,
or 0.875
2 - 2 is the 2nd in sequence, so it is the 2nd section and would start at 1/8 of a degree,
or 0.125
The quad's southeast corner is 47.875¡N; 104.125¡W.
c - c is the northwest corner, which means 1/16 degree has to be added to both N and
W, or 0.0625 to each.
The quarter-quad's southwest corner is 47.9375¡N; 104.1875¡W.
Correspondingly, calc24qq(47.9375, -104.1875) results in "47104h2c".
These codes are only valid for locations with positive latitude and negative longitude.
Parameters:
latitude, longitude: Must be in decimal degree format. May be a single value each or an
array of values each. Must be in the NAD83 projection, or equivalent.