前言
如上图所示，在影像散落着很多目标点，但我们可能对离群点更感兴趣，本篇博文将介绍如何提取离群点。
方法概述
- 对每个点新建一定长度的缓冲区；
- 获得上述缓冲区后，获取缓冲区面积最大值；
- 合并缓冲区相交的feature；
- 设置面积阈值，在我的实验中，阈值为max_area * 1.2;
- 移除超出阈值的缓冲区；
- 获取剩余缓冲区内的点，即为离群的点。
代码
extract.py
from pathlib import Path
from osgeo import ogr, osr, gdal
import os
import shutil
def buffer(inShp, fname, bdistance=0.02):
"""
:param inShp: 输入的矢量路径
:param fname: 输出的矢量路径
:param bdistance: 缓冲区距离
:return:
"""
ogr.UseExceptions()
in_ds = ogr.Open(inShp)
f = open(inShp.replace('.shp','.prj'))
f_ = f.readline()
in_lyr = in_ds.GetLayer()
# 创建输出Buffer文件
driver = ogr.GetDriverByName('ESRI Shapefile')
if Path(fname).exists():
driver.DeleteDataSource(fname)
# 新建DataSource，Layer
out_ds = driver.CreateDataSource(fname)
out_lyr = out_ds.CreateLayer(fname, in_lyr.GetSpatialRef(), ogr.wkbPolygon)
def_feature = out_lyr.GetLayerDefn()
# # 新建area字段
# new_field = ogr.FieldDefn("Area", ogr.OFTReal)
# new_field.SetWidth(40)
# new_field.SetPrecision(20) # 设置面积精度,小数点后16位
# out_lyr.CreateField(new_field)
# 遍历原始的Shapefile文件给每个Geometry做Buffer操作
for feature in in_lyr:
geometry = feature.GetGeometryRef()
buffer = geometry.Buffer(bdistance)
out_feature = ogr.Feature(def_feature)
out_feature.SetGeometry(buffer)
out_lyr.CreateFeature(out_feature)
out_feature = None
out_ds.FlushCache()
del in_ds, out_ds
def area(shpPath):
'''计算面积'''
max_area = 0
driver = ogr.GetDriverByName("ESRI Shapefile")
dataSource = driver.Open(shpPath, 1)
layer = dataSource.GetLayer()
new_field = ogr.FieldDefn("Area", ogr.OFTReal)
new_field.SetWidth(32)
new_field.SetPrecision(16) # 设置面积精度,小数点后16位
layer.CreateField(new_field)
for feature in layer:
geom = feature.GetGeometryRef()
area = geom.GetArea() # 计算面积
if area > max_area:
max_area = area
feature.SetField("Area", area) # 将面积添加到属性表中
layer.SetFeature(feature)
dataSource = None
return max_area
def multipoly2poly(inputshp, outputshp):
"""
:param inputshp: 输入的矢量路径
:param outputshp: 输出的矢量路径
:return:
"""
gdal.UseExceptions()
driver = ogr.GetDriverByName('ESRI Shapefile')
in_ds = driver.Open(inputshp, 0)
in_lyr = in_ds.GetLayer()
if os.path.exists(outputshp):
driver.DeleteDataSource(outputshp)
out_ds = driver.CreateDataSource(outputshp)
out_lyr = out_ds.CreateLayer('poly', geom_type=ogr.wkbPolygon)
for in_feat in in_lyr:
geom = in_feat.GetGeometryRef()
if geom.GetGeometryName() == 'MULTIPOLYGON':
for geom_part in geom:
addPolygon(geom_part.ExportToWkb(), out_lyr)
else:
addPolygon(geom.ExportToWkb(), out_lyr)
def addPolygon(simplePolygon, out_lyr):
featureDefn = out_lyr.GetLayerDefn()
polygon = ogr.CreateGeometryFromWkb(simplePolygon)
out_feat = ogr.Feature(featureDefn)
out_feat.SetGeometry(polygon)
out_lyr.CreateFeature(out_feat)
# print('Polygon added.')
def uni(shpPath, fname):
"""
:param shpPath: 输入的矢量路径
:param fname: 输出的矢量路径
:return:
"""
driver = ogr.GetDriverByName("ESRI Shapefile")
dataSource = driver.Open(shpPath, 1)
layer = dataSource.GetLayer()
# 新建DataSource，Layer
out_ds = driver.CreateDataSource(fname)
out_lyr = out_ds.CreateLayer(fname, layer.GetSpatialRef(), ogr.wkbPolygon)
def_feature = out_lyr.GetLayerDefn()
# 遍历原始的Shapefile文件给每个Geometry做Buffer操作
# current_union = layer[0].Clone()
print('the length of layer:', len(layer))
if len(layer) == 0:
return
for i, feature in enumerate(layer):
geometry = feature.GetGeometryRef()
if i == 0:
current_union = geometry.Clone()
current_union = current_union.Union(geometry).Clone()
if i == len(layer) - 1:
out_feature = ogr.Feature(def_feature)
out_feature.SetGeometry(current_union)
out_lyr.ResetReading()
out_lyr.CreateFeature(out_feature)
def remove_big_buffer(shpPath, outputShp, area_thresold):
'''计算面积'''
driver = ogr.GetDriverByName("ESRI Shapefile")
dataSource = driver.Open(shpPath, 1)
layer = dataSource.GetLayer()
new_field = ogr.FieldDefn("Area", ogr.OFTReal)
new_field.SetWidth(32)
new_field.SetPrecision(16) # 设置面积精度,小数点后16位
layer.CreateField(new_field)
# 新建DataSource，Layer
out_ds = driver.CreateDataSource(outputShp)
out_lyr = out_ds.CreateLayer(outputShp, layer.GetSpatialRef(), ogr.wkbPolygon)
def_feature = out_lyr.GetLayerDefn()
for feature in layer:
geom = feature.GetGeometryRef()
area = geom.GetArea() # 计算面积
if area > area_thresold * 1.2:
continue
feature.SetField("Area", area) # 将面积添加到属性表中
layer.SetFeature(feature)
out_feature = ogr.Feature(def_feature)
out_feature.SetGeometry(geom)
out_lyr.CreateFeature(out_feature)
out_feature = None
out_ds.FlushCache()
del dataSource, out_ds
def intersection(shp1, shp2, outshp):
"""
:param shp1: 缓冲区矢量路径
:param shp2: 目标矢量路径
:param outshp: 输出矢量路径
:return:
"""
driver = ogr.GetDriverByName("ESRI Shapefile")
dataSource1 = driver.Open(shp1, 1)
layer1 = dataSource1.GetLayer()
dataSource2 = driver.Open(shp2, 1)
layer2 = dataSource2.GetLayer()
spatialref = layer2.GetSpatialRef()
# 新建DataSource，Layer
out_ds = driver.CreateDataSource(outshp)
out_lyr = out_ds.CreateLayer(outshp, spatialref, ogr.wkbPolygon)
def_feature = out_lyr.GetLayerDefn()
for feature in layer1:
geom = feature.GetGeometryRef()
for feature_ in layer2:
geom_ = feature_.GetGeometryRef()
if geom.Intersect(geom_) == 1:
out_feature = ogr.Feature(def_feature)
out_feature.SetGeometry(geom_)
out_lyr.CreateFeature(out_feature)
out_ds.FlushCache()
del dataSource1, dataSource2
def mkdir(path):
if not os.path.exists(path):
os.mkdir(path)
def mainfunc(inShp, outshp, bdistance):
temproot = './temp'
mkdir(temproot)
fname = f'{temproot}/buffer.shp'
fname2 = f'{temproot}/buffer2.shp'
buffer(inShp, fname, bdistance=bdistance)
max_area = area(fname)
uni(fname, fname2)
multipoly2poly(fname2, fname)
remove_big_buffer(fname, fname2, max_area)
uni(fname2, fname)
intersection(fname, inShp, outshp)
# remove temporary directory
if os.path.exists(temproot):
shutil.rmtree(temproot)
if __name__ == '__main__':
f = open('config_order.txt')
data = f.readlines()
inShp = data[0].replace('\n', '')
outshp = data[1].replace('\n', '')
bdistance = float(data[2].replace('\n', ''))
print(inShp, outshp)
mainfunc(inShp, outshp, bdistance)
config_order.txt
./data/buildings.shp
isolated_buildings.shp
0.008