OGR距离单位

Question

我在用Python的OGR库计算一个点到一条线的最短距离。可是，我得到的结果和在QGIS上得到的完全不一样。我在想，OGR使用的单位是不是和坐标系统有关？难道OGR用的是度数？如果是这样的话，我该怎么把这些度数转换成米呢？我的代码是这样的：

import ogr

driver = ogr.GetDriverByName('ESRI Shapefile')

roads = driver.Open('G:/Basedata/OR/infra/TigerRoads2010/OR_TIGERroads_2010_merge.shp', 0)
point = driver.Open('U:/My Documents/Tool/shp/testareacentro.shp', 0)

roadslayer = roads.GetLayer()
pointl = point.GetLayer()

roadsfeature = roadslayer.GetNextFeature()
pointf = pointl.GetNextFeature()

roadgeom = roadsfeature.GetGeometryRef()
pointgeom = pointf.GetGeometryRef()

dist = pointgeom.Distance(roadgeom)

print dist

Answer 1

我距离计算不准确的原因是因为我只比较了第一个特征。这个代码的结果和在QGIS中的结果是一样的：

import ogr

driver = ogr.GetDriverByName('ESRI Shapefile')

lineshp = driver.Open('U:/My Documents/Tool/shp/line.shp', 0)
linelyr = lineshp.GetLayer()

pointshp = driver.Open('U:/My Documents/Tool/shp/point.shp', 0)
pointlyr = pointshp.GetLayer()

linefeat = linelyr.GetNextFeature()
pointfeat = pointlyr.GetNextFeature()

point_geom = pointfeat.GetGeometryRef()

distlist = []
while linefeat:
    line_geom = linefeat.GetGeometryRef()
    dist = point_geom.Distance(line_geom)
    distlist.append(dist)
    linefeat.Destroy()
    linefeat = linelyr.GetNextFeature()

print min(distlist)