根据经纬度坐标计算NDS标准下的格网ID

经纬度坐标计算NDS标准下的格网ID"/>

根据经纬度坐标计算NDS标准下的格网ID

根据经纬度坐标计算NDS标准下的格网ID

• 前言
• 一、NDS是如何划分格网并编码的
• 二、计算格网ID的具体实现
• 总结

前言

一、NDS是如何划分格网并编码的

这里直接引用原文。
Navigation Data Standard uses WGS 84, the World Geodetic System dating from 1984, as the standard coordinate reference system for representing latitude and longitude of objects. WGS 84 defines a fixed global reference frame for the whole earth for use in geodesy and navigation. By using this standard coordinate reference system, it is possible to uniquely identify any point on the Earth’s surface – except the North Pole – by two numbers, the x-coordinate and the y-coordinate of the point, where x corresponds to the longitude and y to the latitude.
坐标编码：
For coding coordinates, a scaling factor is applied so that 360° correspond to 232, to exhaust the full range of 32 bit signed integers. In NDS, a coordinate unit corresponds to 90/230 degrees of longitude or latitude. Longitudes range between –180° and +180° and latitudes between –90° and +90°. Hence, coordinate values are in the range of –231≤ x < 231 for longitudes and–230≤ y < 230 for latitudes. This means that for latitudes 31 bits are sufficient. The origin of the coordinate system is the intersection of the WGS 84-0-meridian and the equator.The intention of this encoding is to represent the x-coordinate as signed 32-bit integers: x = x31 x30…x1 x0 and the y-coordinate as signed 31-bit integers: y = y30…y1 y0 with x31 and y30 as the most significant bits and x0 and y0 as the least significant bits.
Morton码介绍：
From a coordinate, which is defined by two integer values for longitude (x) and latitude (y), the Morton code can be derived, which is a single number. Thus, two dimensions are mapped into one dimension. To be more precise, for a given coordinate with x = x31 x30…x1 x0 and y = y30…y1 y0the Morton code c is given by the 63-bit integerc = x31 y30 x30…y1 x1 y0 x0that results from interleaving the bits of the x- and y-coordinate, hence, 0 ≤ c < 263. If stored in a 64-bit integer, the Morton code c is prefixed with a 0 bit, thus always positive.If items are ordered according to their Morton code, we speak of a Morton order.
地图数据分层：
The highest level in a database is labeled level 0. The lowest level is labeled level 15. Not all levels need to be available in a database.Navigation Data Standard uses level 13 for the most detailed routing data. For map display, however, levels below level 13 can be added. For example, it might be useful to store a detailed city map on level 14.
level 0：

level 1：

level 2：

二、计算格网ID的具体实现

直接上代码：

void ConvertXYToRowCol(int64_t x, int64_t y, uint8_t levelId, int32_t &col, int32_t &row)
{const int64_t NDS_180_DEGREES = (int64_t)1 << 31;const int64_t NDS_360_DEGREES = (int64_t)1 << 32;if (x < 0){x += NDS_360_DEGREES;}if (y < 0){y += NDS_180_DEGREES;}int32_t tileSizeFac = 31 - levelId;col = (int32_t)(x >> tileSizeFac);row = (int32_t)(y >> tileSizeFac);
}void CalcMortonCodeToRowCol(uint32_t meshId, uint32_t &row, uint32_t &col)
{int32_t bit = 1;for (int32_t i = 0; i < 32; i++){col |= ((meshId & bit) >> (i * 2) << i);bit <<= 1;row |= ((meshId & bit) >> (i * 2 + 1) << i);bit <<= 1;}
}uint32_t ConvertPointToMortonCode(int64_t x, int64_t y)
{int64_t bit = 1;int64_t mortonCode = 0;if (y < 0){y += 0x7FFFFFFF;}y <<= 1;for (int32_t i = 0; i < 32; i++){mortonCode |= (x & bit);x <<= 1;bit <<= 1;mortonCode |= (y & bit);y <<= 1;bit <<= 1;}return (uint32_t)mortonCode;
}
/**
* mesh is also the name of grid
* @param[in] level   the level id 0 ~ 13.
* @param[in] x   longitude in degree.
* @param[in] y   latitude in degree.
* @param[out] tileId   the morton code and level id, you can also use (meshId << 32 | levelId).
*/
void getTileId(uint8_t levelId, double x, double y, TileId &tileId)
{int64_t x = (int64_t)(x * 4294967296 / 360);int64_t y = (int64_t)(y * 4294967296 / 360);int32_t col = 0, row = 0;ConvertXYToRowCol(x, y, levelId, col, row);tileId.meshId = ConvertPointToMortonCode(col, row);tileId.levelId = level;
}

也可以根据矩形范围计算覆盖的格网，即计算出左上右下所在格网的行列号，根据行列号得到所有的Morton码

总结

结合NDS标准的文档说明，理解格网划分的设计，计算格网ID并不难。