3-degree band/6-degree band

The topographic maps of and adopt a 6-degree band projection, that is, the longitude difference is 6 degrees, starting from the zero-degree meridian, and each longitude difference of 6 degrees from west to east is a projection band, the world is divided into 60 bands, with 1, 2, 3, 4, 5 ,...... Represents. That is, the eastern longitude 0 ~ The longitude of the center longitude is 3 degrees east longitude, And the longitude is 6 degrees east longitude ~ 12 degrees is the second band, and the longitude of the central longitude is 9 degrees ......
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The-10 thousand Topographic Map adopts a 3-degree band. It starts from the longitude line of the east longitude 1.5 degrees and ranges from 1 to 2, 3 ,...... It indicates that a total of 120 projection bands are divided around the world, that is, the longitude 1.5 ~ The longitude of the central longitude is 3 degrees, and the longitude of the longitude is 4.5 ~ The longitude of the central longitude of the 7.5-degree belt is 6 degrees east longitude.
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China's longitude ranges from 73 ° to 135 ° to the West, which can be divided
Eleven in the Six-Degree belt (belt 13-belt 23). The central longitude lines of each belt are (75 °, 81 ° ,...... 123 °, 129 °, 135 °)
Carry 22 of the three degrees (24-45 ). The central longitude of each belt is (72 °, 75 ° ,...... 132 °, 135 °)
The six-degree belt can be used for small and medium scale (such as) ing, and the three-degree belt can be used for large-scale (such as) ing. The urban construction coordinates usually use the Gaussian projection of the Three-degree belt. (That is, and are projected by Gaussian-kerlenge with a 3-degree band, and by Gaussian-kerlenge with a 6-degree band between and, using Lambert (positive-axis equal-angle Cut Cone projection) or Albert TS (positive-axis equal-product Cut Cone projection )) // Added by zhangjun at 2011-1-4
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How to determine whether the projection coordinate is 3-degree coordinate or 6-degree Coordinate
For example, (4231898,21655933) where 21 is the belt number, the same defined East pseudo offset value also needs to be added with a number, for example, the East pseudo offset value of 21 is 21500000 meters. If the longitude of your work zone ranges from 120 degrees to 126 degrees, the coordinate system is a 6-degree coordinate system with a central longitude of 123 degrees.
For example, (2949320,36353822) 36 indicates the belt number. It is known that the location is near Guiyang City. On the map, we can see that the longitude of Guiyang is about 108 degrees east longitude, therefore, it can be 36*3 = 108. Therefore, the coordinate system is a 3-degree coordinate system with a central longitude of 108 degrees. But it cannot be 6 degree band: 36*6 = 216