一、定義空間字段：
因?yàn)樵摪姹局С謩?chuàng)建Geography字段類型，因此創(chuàng)建空間字段不同于之前版本，采用了如下形式：
geom?=Column(Geometry('POLYGON’))
二、空間函數(shù)的使用：
需要注意的是所有函數(shù)都帶有ST_前綴，這也是為了與postgis寫(xiě)法一致.
函數(shù)的使用方法：
第一種是使用func，例如在orm中你可以：
Session.query(func.ST_Area(Lake.geom))或Session.query(Lake.geom.ST_Area())?進(jìn)行面積查詢
不使用orm你可以：
select([func.ST_Area(lake_table.c.geom)])
三、支持wkt和wkb格式
例如WKTElement('POINT(5 45)’)和WKTElement('POINT(5 45)',srid=4326)對(duì)應(yīng)著Point類型的Geometry，和postgis中的ST_GeomFromText效果相同。
同時(shí)支持與shapely庫(kù)的空間類型互相轉(zhuǎn)換，詳情請(qǐng)查閱geoalchemy2.shape.from_shape和geoalchemy2.shape.to_shape方法
空間函數(shù)整理：（谷歌機(jī)翻加上了自己的一點(diǎn)調(diào)整）
函數(shù)名 ?返回類型?
2.1?geometry訪問(wèn)相關(guān)
（'ST_Envelope'，types.Geometry，
?????'返回提供的geometry的外邊框，雙精度（float8）’）
????（'ST_GeometryN'，無(wú)，
?????'如果幾何是``GEOMETRYCOLLECTION``，``（MULTI）POINT``，``（MULTI）LINESTRING``，``MULTICURVE``或``（MULTI）POLYGON``，``POLYHEDRALSURFACE``，則返回基于1的第N個(gè)幾何， 否則返回``None``。），
????（'ST_GeometryType'，無(wú)，
?????'返回``ST_Geometry``返回值的幾何類型。'），
????（'ST_IsValid'，無(wú)，
?????如果``ST_Geometry``返回的空間數(shù)據(jù)有效，則返回``True``。'），
????（'ST_NPoints'，無(wú)，
?????'返回Geometry數(shù)據(jù)中的節(jié)點(diǎn)數(shù)。'），
????（'ST_SRID'，無(wú)，
?????‘返回Geometry數(shù)據(jù)的SRID數(shù)值，該數(shù)值參考spatial_ref_sys表中的定義）
????（'ST_X'，無(wú)，
? ? ?返回點(diǎn)的X坐標(biāo)，如果不可用，則返回“無(wú)”。輸入必須是一個(gè)Point類型數(shù)據(jù)），
????（'ST_Y'，無(wú)，返回點(diǎn)的Y坐標(biāo)，如果不可用，則返回“無(wú)”。輸入必須是一個(gè)Point類型數(shù)據(jù)）
????（'ST_Z'，無(wú)，返回點(diǎn)的Z坐標(biāo)，如果不可用，則返回“無(wú)”。輸入必須是一個(gè)Point類型數(shù)據(jù)）
? ? 2.2 geometry編輯相關(guān)
????（'ST_Transform'，types.Geometry，
?????'返回一個(gè)新的幾何體，其坐標(biāo)轉(zhuǎn)換為輸入的SRID'），
? ? 2.3 geometry輸出
????（'ST_AsBinary'，無(wú)，轉(zhuǎn)化成WKB），
????（'ST_AsEWKB'，無(wú)，轉(zhuǎn)化成EWKB），
????（'ST_AsTWKB'，無(wú)，轉(zhuǎn)化成TWKB），
????（'ST_AsGeoJSON'，無(wú)，'將geometry轉(zhuǎn)化成GeoJSON元素返回。'），
????（'ST_AsGML'，無(wú)，'將geometry轉(zhuǎn)化成GML版本2或3。'），
????（'ST_AsKML'，無(wú)，
'將geometry轉(zhuǎn)化為KML元素返回。多個(gè)類型。默認(rèn)參數(shù)：'version = 2，default precision= 15'），
????（'ST_AsSVG'，無(wú)，
?????'返回輸入geometry或geography的SVG格式數(shù)據(jù)'），
????（'ST_AsText'，無(wú)，返回輸入geometry的WKT格式，沒(méi)有SRID信息）
????（'ST_AsEWKT'，無(wú)，
?????'返回輸入geometry的EWKT格式數(shù)據(jù)，具有SRID信息。'），
? ? 2.4 空間關(guān)系和測(cè)量
（'ST_Area'，無(wú)，如果是polygon或multi-polygon，則返回平面面積；對(duì)于geometry類型的面積單位取決于SRID。對(duì)于geography類型面積單位為平方米），
????（'ST_Azimuth'，無(wú)，返回pointb和pointb之間的角度的弧度值，順時(shí)針計(jì)算，12 = 0; 3 = PI / 2; 6 = PI; 9 = 3PI / 2），
????（'ST_Centroid'，types.Geometry，返回geometry的幾何中心），
????（'ST_Contains'，無(wú)，A是否包含B'），
????（'ST_ContainsProperly'，A是否完全包含B，不內(nèi)切），
????（'ST_Covers'，無(wú)，A是否包含B，可以內(nèi)切，
????（'ST_CoveredBy'，沒(méi)有，B是否包含A），
????（'ST_Crosses'，無(wú)，
?????如果提供的幾何有一些但不是全部，則返回``True``
?????'內(nèi)部點(diǎn)共同點(diǎn)。'），
????（'ST_Disjoint'，無(wú)，
?????如果幾何不“空間相交”，則返回``True``??- 如果'
?????“他們不共享任何空間?！保?，
????（'ST_Distance'，無(wú)，
?????'對(duì)于幾何類型返回二維笛卡爾最小距離'
?????'（基于空間參考）在投影單位中的兩個(gè)幾何之間。為''
?????'地理類型默認(rèn)返回'之間的球形最小距離'
?????'米的兩個(gè)地理位置。'），
????（'ST_Distance_Sphere'，無(wú)，
?????'返回兩個(gè)lon / lat幾何之間的最小距離（以米為單位）。使用'
?????'球形地球，半徑6370986米。比...快 '
?????'``ST_Distance_Spheroid``，但不太準(zhǔn)確。 PostGIS版本'
?????'在1.5之前只實(shí)現(xiàn)積分。'），
????（'ST_DFullyWithin'，沒(méi)有，
?????'如果所有幾何都在指定的范圍內(nèi)，則返回``True``
?????'彼此的距離'）
'ST_DWithin'，沒(méi)有，
?????如果空間圖形在另一個(gè)空間圖形指定的距離內(nèi)，則返回True。單位視空間坐標(biāo)系而定，geography的單位為米。默認(rèn)為球面，柵格數(shù)據(jù)默認(rèn)為非球面
????（'ST_Intersects'，無(wú)，
?????如果geometry/geography相交，則返回true。
????（'ST_Length'，無(wú)，
?????'如果它是一個(gè)LINESTRING或MULTILINESTRING，則返回幾何的2d長(zhǎng)度。幾何以空間參考為單位，geography以米為單位（默認(rèn)球體）'），
????（'ST_LineLocatePoint'，無(wú)，
?????'返回一個(gè)介于0和1之間的浮點(diǎn)數(shù)，表示LineString上最接近給定Point的點(diǎn)的距離占LineString總長(zhǎng)的百分比），
????（'ST_OrderingEquals'，無(wú)，
?????如果給定的幾何表示相同的幾何，則返回``True``
?????'和點(diǎn)的方向順序相同。'），
????（'ST_Overlaps'，無(wú)，
?????如果Geometries共享空間，則返回``True``，是相同的'
?????'維度，但彼此不完全包含。'），
????（'ST_Perimeter'，無(wú)，
?????'返回ST_Surface邊界的長(zhǎng)度測(cè)量值或'
?????'ST_MultiSurface幾何或地理。 （多邊形，多邊形）。 “
?????'幾何測(cè)量以空間參考為單位，地理是'
?????'米。'），
????（'ST_Project'，types.Geography，
?????'返回一個(gè)從起始點(diǎn)投射的``POINT``使用距離'
?????'米和軸承（方位角）以弧度表示。'），
????（'ST_Relate'，無(wú)，
?????'如果此幾何與空間相關(guān)'，則返回``True``
?????'另一個(gè)幾何，通過(guò)測(cè)試內(nèi)部之間的交叉點(diǎn)，'
?????'由值指定的兩個(gè)幾何的邊界和外部'
?????'在intersectionMatrixPattern中。如果沒(méi)有intersectionMatrixPattern'
?????'傳入，然后返回最大的intersectionMatrixPattern'
?????'涉及兩種幾何形狀。'），
????（'ST_Touches'，無(wú)，
?????如果幾何有至少一個(gè)共同點(diǎn)，'返回``True``
?????'但他們的內(nèi)部不相交。'），
????（'ST_Within'，沒(méi)有，
?????'如果幾何A完全在幾何B'內(nèi)，則返回``True``，
????＃
????＃幾何處理
????＃
????（'ST_Buffer'，types.Geometry，
?????'對(duì)于幾何體：返回表示其所有點(diǎn)的幾何體'
?????'與此幾何的距離小于或等于距離。 “
?????'計(jì)算在此幾何的空間參照系中。\ n \ n'
?????'對(duì)于地理：使用平面變換包裝。介紹1.5'
?????'支持不同的端蓋和斜接設(shè)置來(lái)控制形狀。'），
????（'ST_Difference'，types.Geometry，
?????'返回表示幾何A的那部分的幾何'
?????'與幾何B不相交''），
????（'ST_Dump'，types.GeometryDump，
?????'返回一組geometry_dump（geom，path）行，組成''
?????'geometry g1。'），
????（'ST_DumpPoints'，types.GeometryDump，
?????'返回一組所有點(diǎn)的geometry_dump（geom，path）行'
?????'構(gòu)成一個(gè)幾何。'），
????（'ST_Intersection'，types.Geometry，
?????'返回表示geomA和'的共享部分的幾何
?????“geomB。地理位置實(shí)現(xiàn)了對(duì)幾何體的轉(zhuǎn)換'
?????'交叉點(diǎn)然后轉(zhuǎn)換回WGS84。'），
????（'ST_LineMerge'，types.Geometry，
?????'返回一個(gè)（一組）LineString（s）形成的縫合在一起'
?????'MULTILINESTRING的組成線工作。'），
????（'ST_LineSubstring'，types.Geometry，
?????'返回一個(gè)線串作為輸入的一個(gè)子串開(kāi)始和'
?????'以總共2d長(zhǎng)度的給定分?jǐn)?shù)結(jié)束。第二和第三'
?????'參數(shù)是介于0和1之間的float8值。這僅適用于'
?????“線串。要使用連續(xù)的MULTILINESTRING，請(qǐng)使用'
?????'與ST_LineMerge結(jié)合。'
?????“”
?????'如果\'開(kāi)始\'和\'結(jié)尾\'具有相同的值，這相當(dāng)于'
?????'到ST_LineInterpolatePoint。'），
????（'ST_Union'，types.Geometry，
?????'返回表示'的點(diǎn)集聯(lián)合的幾何'
?????'的幾何形狀。'），
????（'ST_Simplify'，types.Geometry，
?????'使用'返回給定幾何的“簡(jiǎn)化”版本
?????'Douglas-Peucker算法。'），
????＃
????#Raster構(gòu)造函數(shù)
????＃
????（'ST_GeomFromText'，types.Geometry，
?????'從OGC著名文本構(gòu)造一個(gè)PostGIS ST_Geometry對(duì)象'
?????'表示。’），
（'ST_GeomFromEWKT'，types.Geometry，
?????'從OGC Extended Well-Known構(gòu)造一個(gè)PostGIS ST_Geometry對(duì)象'
?????'text（EWKT）表示。'），
????（'ST_GeomFromEWKB'，types.Geometry，
?????'從OGC Extended Well-Known構(gòu)造一個(gè)PostGIS ST_Geometry對(duì)象'
?????'二進(jìn)制（EWKB）表示。'），
????（'ST_GeogFromText'，types.Geography，
?????'從眾所周知的文本中返回地理對(duì)象或擴(kuò)展眾所周知的'
?????'表示。'），
????（'ST_AsRaster'，types.Raster，
?????（'將PostGIS幾何體轉(zhuǎn)換為PostGIS柵格。'，'RT_ST_AsRaster'）），
????＃
????#Raster訪問(wèn)者
????＃
????（'ST_Height'，無(wú)，
?????（'返回柵格的高度，以像素為單位。'，'RT_ST_Height'）），
????（'ST_Width'，無(wú)，
?????（'返回柵格的寬度，以像素為單位。'，'RT_ST_Width'）），
????＃
????#Raster Pixel Accessors和Setters
????＃
????（'ST_Value'，無(wú)，
?????（'返回給定columnx，rowy pixel或at'中給定band的值
??????'一個(gè)特定的幾何點(diǎn)。樂(lè)隊(duì)編號(hào)從1開(kāi)始并假設(shè)為'
??????'如果沒(méi)有指定則為1。如果``exclude_nodata_value``設(shè)置為'
??????'``false``，然后所有像素都包含nodata像素被認(rèn)為是'
??????'相交并返回值。如果沒(méi)有傳遞``exclude_nodata_value``'
??????'然后從柵格的元數(shù)據(jù)中讀取它。'，'RT_ST_Value’））
翻譯不動(dòng)了，貼上原文：
('ST_Envelope', types.Geometry,
'Returns a geometry representing the double precision (float8) bounding'
'box of the supplied geometry.'),
('ST_GeometryN',None,
'Return the 1-based Nth geometry if the geometry is a '
'``GEOMETRYCOLLECTION``, ``(MULTI)POINT``, ``(MULTI)LINESTRING``, '
'``MULTICURVE`` or ``(MULTI)POLYGON``, ``POLYHEDRALSURFACE`` Otherwise, '
'return ``None``.'),
('ST_GeometryType',None,
'Return the geometry type of the ``ST_Geometry`` value.'),
('ST_IsValid',None,
'Returns ``True`` if the ``ST_Geometry`` is well formed.'),
('ST_NPoints',None,
'Return the number of points (vertices) in a geometry.'),
('ST_SRID',None,
'Returns the spatial reference identifier for the ``ST_Geometry`` as '
'defined in ``spatial_ref_sys`` table.'),
('ST_X',None,
'Return the X coordinate of the point, or ``None`` if not available. '
'Input must be a point.'),
('ST_Y',None,
'Return the Y coordinate of the point, or ``None`` if not available. '
'Input must be a point.'),
('ST_Z',None,
'Return the Z coordinate of the point, or ``None`` if not available. '
'Input must be a point.'),
#
# Geometry Editors
#
('ST_Transform', types.Geometry,
'Return a new geometry with its coordinates transformed to the SRID '
'referenced by the integer parameter.'),
#
# Geometry Outputs
#
('ST_AsBinary',None,
'Return the Well-Known Binary (WKB) representation of the geometry/'
'geography without SRID meta data.'),
('ST_AsEWKB',None,
'Return the Well-Known Binary (WKB) representation of the geometry/'
'geography with SRID meta data.'),
('ST_AsTWKB',None,
'Returns the geometry as TWKB, aka "Tiny Well-Known Binary"'),
('ST_AsGeoJSON',None,'Return the geometry as a GeoJSON element.'),
('ST_AsGML',None,'Return the geometry as a GML version 2 or 3 element.'),
('ST_AsKML',None,
'Return the geometry as a KML element. Several variants. Default '
'version=2, default precision=15'),
('ST_AsSVG',None,
'Returns a Geometry in SVG path data given a geometry or geography '
'object.'),
('ST_AsText',None,
'Return the Well-Known Text (WKT) representation of the geometry/'
'geography without SRID metadata.'),
('ST_AsEWKT',None,
'Return the Well-Known Text (WKT) representation of the geometry/'
'geography with SRID metadata.'),
#
# Spatial Relationships and Measurements
#
('ST_Area',None,
'Returns the area of the surface if it is a polygon or multi-polygon. '
'For ``geometry`` type area is in SRID units. For ``geography`` area is '
'in square meters.'),
('ST_Azimuth',None,
'Returns the angle in radians from the horizontal of the '
'vector defined by pointA and pointB. Angle is computed clockwise from '
'down-to-up: on the clock: 12=0; 3=PI/2; 6=PI; 9=3PI/2.'),
('ST_Centroid', types.Geometry,
'Returns the geometric center of a geometry.'),
('ST_Contains',None,
'Returns ``True`` if and only if no points of B lie in the exterior of '
'A, and at least one point of the interior of B lies in the interior '
'of A.'),
('ST_ContainsProperly',None,
'Returns ``True`` if B intersects the interior of A but not the boundary '
'(or exterior). A does not contain properly itself, but does contain '
'itself.'),
('ST_Covers',None,
'Returns ``True`` if no point in Geometry B is outside Geometry A'),
('ST_CoveredBy',None,
'Returns ``True`` if no point in Geometry/Geography A is outside Geometry'
'/Geography B'),
('ST_Crosses',None,
'Returns ``True`` if the supplied geometries have some, but not all, '
'interior points in common.'),
('ST_Disjoint',None,
'Returns ``True`` if the Geometries do not "spatially intersect" - if '
'they do not share any space together.'),
('ST_Distance',None,
'For geometry type Returns the 2-dimensional cartesian minimum distance '
'(based on spatial ref) between two geometries in projected units. For '
'geography type defaults to return spheroidal minimum distance between '
'two geographies in meters.'),
('ST_Distance_Sphere',None,
'Returns minimum distance in meters between two lon/lat geometries. Uses '
'a spherical earth and radius of 6370986 meters. Faster than '
'``ST_Distance_Spheroid``, but less accurate. PostGIS versions '
'prior to 1.5 only implemented for points.'),
('ST_DFullyWithin',None,
'Returns ``True`` if all of the geometries are within the specified '
'distance of one another'),
('ST_DWithin',None,
'Returns ``True`` if the geometries are within the specified distance of '
'one another. For geometry units are in those of spatial reference and '
'for geography units are in meters and measurement is defaulted to '
'``use_spheroid=True`` (measure around spheroid), for faster check, '
'``use_spheroid=False`` to measure along sphere.'),
('ST_Equals',None,
'Returns ``True`` if the given geometries represent the same geometry. '
'Directionality is ignored.'),
('ST_Intersects',None,
'Returns ``True`` if the Geometries/Geography "spatially intersect in '
'2D" - (share any portion of space) and ``False`` if they don\'t (they '
'are Disjoint). For geography -- tolerance is 0.00001 meters (so any '
'points that close are considered to intersect)'),
('ST_Length',None,
'Returns the 2d length of the geometry if it is a linestring or '
'multilinestring. geometry are in units of spatial reference and '
'geography are in meters (default spheroid)'),
('ST_LineLocatePoint',None,
'Returns a float between 0 and 1 representing the location of the '
'closest point on LineString to the given Point, as a fraction of '
'total 2d line length.'),
('ST_OrderingEquals',None,
'Returns ``True`` if the given geometries represent the same geometry '
'and points are in the same directional order.'),
('ST_Overlaps',None,
'Returns ``True`` if the Geometries share space, are of the same '
'dimension, but are not completely contained by each other.'),
('ST_Perimeter',None,
'Return the length measurement of the boundary of an ST_Surface or '
'ST_MultiSurface geometry or geography. (Polygon, Multipolygon). '
'geometry measurement is in units of spatial reference and geography is '
'in meters.'),
('ST_Project', types.Geography,
'Returns a ``POINT`` projected from a start point using a distance in '
'meters and bearing (azimuth) in radians.'),
('ST_Relate',None,
'Returns ``True`` if this Geometry is spatially related to '
'anotherGeometry, by testing for intersections between the Interior, '
'Boundary and Exterior of the two geometries as specified by the values '
'in the intersectionMatrixPattern. If no intersectionMatrixPattern is '
'passed in, then returns the maximum intersectionMatrixPattern that '
'relates the 2 geometries.'),
('ST_Touches',None,
'Returns ``True`` if the geometries have at least one point in common, '
'but their interiors do not intersect.'),
('ST_Within',None,
'Returns ``True`` if the geometry A is completely inside geometry B'),
#
# Geometry Processing
#
('ST_Buffer', types.Geometry,
'For geometry: Returns a geometry that represents all points whose '
'distance from this Geometry is less than or equal to distance. '
'Calculations are in the Spatial Reference System of this Geometry.\n\n'
'For geography: Uses a planar transform wrapper. Introduced in 1.5 '
'support for different end cap and mitre settings to control shape.'),
('ST_Difference', types.Geometry,
'Returns a geometry that represents that part of geometry A that does '
'not intersect with geometry B.'),
('ST_Dump', types.GeometryDump,
'Returns a set of geometry_dump (geom,path) rows, that make up a '
'geometry g1.'),
('ST_DumpPoints', types.GeometryDump,
'Returns a set of geometry_dump (geom,path) rows of all points that '
'make up a geometry.'),
('ST_Intersection', types.Geometry,
'Returns a geometry that represents the shared portion of geomA and '
'geomB. The geography implementation does a transform to geometry to do '
'the intersection and then transform back to WGS84.'),
('ST_LineMerge', types.Geometry,
'Returns a (set of) LineString(s) formed by sewing together the '
'constituent line work of a MULTILINESTRING.'),
('ST_LineSubstring', types.Geometry,
'Return a linestring being a substring of the input one starting and '
'ending at the given fractions of total 2d length. Second and third '
'arguments are float8 values between 0 and 1. This only works with '
'LINESTRINGs. To use with contiguous MULTILINESTRINGs use in '
'conjunction with ST_LineMerge.'
''
'If\'start\'and\'end\'have the same value this is equivalent '
'to ST_LineInterpolatePoint.'),
('ST_Union', types.Geometry,
'Returns a geometry that represents the point set union of the '
'Geometries.'),
('ST_Simplify', types.Geometry,
'Returns a "simplified" version of the given geometry using the '
'Douglas-Peucker algorithm.'),
#
# Raster Constructors
#
('ST_GeomFromText', types.Geometry,
'Constructs a PostGIS ST_Geometry object from the OGC Well-Known text '
'representation.'),
('ST_GeomFromEWKT', types.Geometry,
'Constructs a PostGIS ST_Geometry object from the OGC Extended Well-Known '
'text (EWKT) representation.'),
('ST_GeomFromEWKB', types.Geometry,
'Constructs a PostGIS ST_Geometry object from the OGC Extended Well-Known '
'binary (EWKB) representation.'),
('ST_GeogFromText', types.Geography,
'Returns a geography object from the well-known text or extended well-known '
'representation.'),
('ST_AsRaster', types.Raster,
('Converts a PostGIS geometry to a PostGIS raster.','RT_ST_AsRaster')),
#
# Raster Accessors
#
('ST_Height',None,
('Returns the height of the raster in pixels.','RT_ST_Height')),
('ST_Width',None,
('Returns the width of the raster in pixels.','RT_ST_Width')),
#
# Raster Pixel Accessors and Setters
#
('ST_Value',None,
('Returns the value of a given band in a given columnx, rowy pixel or at '
'a particular geometric point. Band numbers start at 1 and assumed to '
'be 1 if not specified. If ``exclude_nodata_value`` is set to '
'``false``, then all pixels include nodata pixels are considered to '
'intersect and return value. If ``exclude_nodata_value`` is not passed '
'in then reads it from metadata of raster.','RT_ST_Value'))
