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如何计算出哪个 shapefile（郊区）包含 PHP 中给定的经纬度点

发布于 2024-12-14 03:58:04 字数 217 浏览 3 评论 0原文

我只能访问 PHP5（没有 PostGIS）

我有一堆郊区形状文件，以及一些带有经纬度点的事件。我对 shapefile 的经验为零。

检查哪些 shapefile 包含这些经纬度点的最佳方法是什么（仅使用 PHP）？

我是否将形状文件转换为经纬度多边形并使用标准多边形点交点方程？

或者这些是一些很棒的用于加载/使用 Shapefile 的 PHP 库？

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能否归途做我良人 2024-12-21 03:58:04

每个shapefile由3部分组成，shp、shx、dbf。 shp 文件包含几何图形，shx 是帮助访问 shp 的索引，dbf 是包含每个记录的数据的普通旧数据库文件。

您可以按如下方式从 shp 文件中提取边界框，

$handle = fopen("path/to/file.shp","rb");
fseek($handle, 36);
$min_x = unpack("d",fread($handle,8);
$min_y = unpack("d",fread($handle,8);
$max_x = unpack("d",fread($handle,8);
$max_y = unpack("d",fread($handle,8);
// Note, this code will only work on a little-endian machine
// You'll need to do a byte swap on big endian systems

然后可以测试给定事件是否位于 shapefile 的边界框中。

if (($event_x >= $min_x) && ($event_x <= $max_x) 
      && ($event_y >= $min_y) && ($event_y <= $max_y))

您可以将其作为一个循环，并获取与给定事件重叠的 shapefile 的子集。这并不意味着您的事件位于给定形状文件中的多边形内，但它会让您接近。如果您需要精确的解决方案，则必须提取多边形并在多边形测试中进行点。

免责声明：考虑上面的代码伪代码，我不懂php，所以可能存在一些错误。另外，如果您可以切换到 python，事情会变得容易得多，现有的库提供 shapefile 解析和空间索引，因此您可以以高效的方式准确确定点与哪些多边形相交。

参考：ESRI Shapefile 白皮书，http://www.esri.com/library/whitepapers /pdfs/shapefile.pdf

Each shapefile consists of 3 parts, shp,shx,dbf. The shp file contains the geometry, shx is an index to help access the shp, the dbf is plain old dbase file that contains data for each record.

You can extract the bounding box from the shp file as follows,

$handle = fopen("path/to/file.shp","rb");
fseek($handle, 36);
$min_x = unpack("d",fread($handle,8);
$min_y = unpack("d",fread($handle,8);
$max_x = unpack("d",fread($handle,8);
$max_y = unpack("d",fread($handle,8);
// Note, this code will only work on a little-endian machine
// You'll need to do a byte swap on big endian systems

Then you can test to see if a given event lies in the shapefile's bounding box.

if (($event_x >= $min_x) && ($event_x <= $max_x) 
      && ($event_y >= $min_y) && ($event_y <= $max_y))

You can put this is a loop and get a subset of your shapefile that overlap with a given event. This doesn't mean you event is inside a polygon in a given shapefile, but it'll get you close. If you need an exact solution you'll have to extract the polygons and do a point in polygon test.

Disclaimer: Consider the above code pseudo code, I don't know php, so there are probably some bugs. Also, If you can switch to python things get a lot easier, there are existing libraries that provide shapefile parsing and spatial indexing, so you can determine exactly which polygons a point intersects with in a highly efficient manner.

Ref: ESRI Shapefile Whitepaper, http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf

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