MapServer Tutorial——MapServer7.2.1教程学习——第一节用例实践：Example1.6 Defining Projections and Extents
一、前言
当在mapfile文件中定义PROJECTION对象时，MapServer将图层和投影信息传递给proj.4库执行重投影。详情请看：https://proj4.org/。
有数以千计的地理参考系统。为了将数据集与不同地理参考系统结合到地图中，必须将数据集转换（投影）到地图中选定的地理参考系统。
PROJECTION在MapServe中，则是制定使用哪种地理残念考系统。（同属理解，就是你当前的数据是使用哪种坐标信息。）
既然PROJECTION是用来指定数据所使用的坐标系信息，那么，它出现的位置就应该在需要使用显示数据的地方。
第一个就是mapfile的MAP标签里面，用来定义输出坐标系；第二个位置就是LAYER标签里面，定义输入坐标系。
二、在MapServer中使用投影（Projections with MapServer）
如果要使用PROJECTION，你必须在mapfile中MAP标签下面定义一个输出PROJECTION。然后每个LAYER里面必须定义输入坐标系。（注意是必须定义）
PROJECTION对象是有一系列的PROJ.4库关键字构成。要么直接用关键书写；要么引用EPSG文件。格式如下。（EPSG详见：https://www.mapserver.org/glossary.html#term-epsg）
EPSG代码是与坐标系定义相关联的数字代码。如：EPSG:4326（EPSG:4326就是WGS84）
ESPG相关资料：
- 官网：http://www.epsg.org/
- ESPG数据资料：http://spatialreference.org/
#直接使用PROJ.4库关键字构建PROJECTION PROJECTION
"proj=utm"
"ellps=GRS80"
"datum=NAD83"
"zone=15"
"units=m"
"north"
"no_defs"
END #通过EPSG构建PROJECTION
PROJECTION
"init=epsg:26915"
END
三、创建Example1.6站点
在cmd中输入：cd /d E:\SvnWorkspace\LY_WEB_GIS\branches\Documents\ms4w-mapserver-for-wimdows\release-1911-x64-gdal-2-3-3-mapserver-7-2-1\apps
在cmd中输入：md Example1.6
在cmd中输入：cd Example1.6
在cmd中输入：md data
在cmd中输入：md fonts
在cmd中输入：md symbols
在cmd中输入：md logs
在cmd中输入：cd.>web.config
在cmd中输入：cd.>example1_6.map
在cmd中输入：cd data
在cmd中输入：md raster
将 app/tutorial/fonts 文件夹中的所有文件拷贝到 apps/Example1.6/fonts 文件夹中
将 app/tutorial/symbols 文件夹中的 symbols35.sym 文件拷贝到 apps/Example1.6/symbols 文件夹中
将 app/tutorial/data 文件夹中的 states_ugl.dbf、states_ugl.shp、states_ugl.shx 文件拷贝到 apps/Example1.6/data 文件夹中
将 app/tutorial/data/raster 中的 mod09a12003161_ugl_ll_8bit.tif 文件拷贝到 apps/Example1.6/data/raster 文件夹中
修改 web.config 文件如下：
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<handlers>
<add name="MapServerFastCgi" path="*" verb="*" type="" modules="FastCgiModule"
scriptProcessor="E:\SvnWorkspace\LY_WEB_GIS\branches\Documents\ms4w-mapserver-for-wimdows\release-1911-x64-gdal-2-3-3-mapserver-7-2-1\bin\mapserv.exe"
resourceType="Unspecified" requireAccess="Script" allowPathInfo="false" preCondition="" />
</handlers>
<caching enabled="true" enableKernelCache="true" />
</system.webServer>
</configuration>
修改MapFIle（example1_6.map）文件如下：
# The annotated map file (sort of)
# Created by Pericles S. Nacionales for the MapServer tutorial
# 20050408
#
# MapServer map file uses the pound sign (#) to denote the start of a line
# comment--each line that needs to be commented has to be prepended with a "#".
#
# Map files begin with MAP keyword to signify the start of the map object.
# Well, the entire map file is THE map object. Enclosed between MAP and END
# at the very bottom of this map file, are keyword/value pairs and other
# objects.
MAP
#IMAGETYPE PNG24
IMAGETYPE PNG
#EXTENT -97.238976 41.619778 -82.122902 49.385620 # WGS84 经纬度坐标数据
#EXTENT 201621.496941 -294488.285333 1425518.020722 498254.511514 # LAEA 原始官网mapfile中的数据
EXTENT 230147.11 -371641.81 1285308.08 632638.93 # LAEA 自己通过命令计算的坐标数据
#EXTENT -97.5 41.619778 -82.122902 49.38562 # Geographic
SIZE 400 300
SHAPEPATH "./data"
SYMBOLSET "./symbols/symbols35.sym"
FONTSET "./fonts/fonts.list" # The projection object is typically used within the map and the layer
# objects. You only define it once within the map object and this definition
# becomes your output projection--MapServer will render your maps in this
# projection. You also use the projection object within the layer object to
# define your input projection. Your layers can be in different
# projections--MapServer will reproject them into your output projection.
# If no projection is defined within the layer object, MapServer assumes
# your input projection is the same as your output projection. This is not
# a required object unless you're creating a map file that supports one of
# the OGC interoperability web services specifications (WMS/WFS/WCS).
#
# This is the output PROJECTION definition ------
PROJECTION
# Projection parameters can be defined in two ways...
# This is the traditional PROJ.4 definition of Lambert Azimuthal Equal-Area
# projection for the Continental U.S.
"proj=laea"
"ellps=clrk66"
"lat_0=45"
"lon_0=-100" # Alternatively, you can specify an EPSG code.
# This is the EPSG code for Lambert Azimuthal Equal-Area
# projection for the U.S.
#
# "init=epsg:2163"
END # End of the output Projection definition --- # Layer objects are defined beneath the map object. You need at least one
# layer defined in your map file before you can display a map... You can
# define as many layers as you'd like although a limit is typically hard-coded
# in map.h in the MapServer source. The default limit is set at 100. You'd
# have to have a very specialized application to need more than 100 layers in
# your application.
#
# Start of LAYER DEFINITIONS ---------------------------------------------
LAYER # States polygon layer begins here
NAME states_polygon
DATA states_ugl
STATUS OFF
TYPE POLYGON # Here's an example of the input projection definition.
# EPSG:4326 is code for geographic (latlong) projection
# using the WGS84 datum.
#
# PROJECTION objects within the LAYER object define the input
# projection--this is the native projection of your data.
PROJECTION
"init=epsg:4326"
END # CLASSITEM defines the non-spatial attribute that you will be using to
# separate a layer into classes. This attribute will be in the DBF file
# of your shapefile (it will be different for each data format). In this
# example the shapefile states_ugl has an associated database
# (states_ugl.dbf) that contains an attribute called "CLASS". You will be
# using two values in the CLASS attribute to separate the classes (also
# called themes) used in this layer--land and water. CLASSITEM is used in
# association with the EXPRESSION parameter in the CLASS object. See below.
CLASSITEM "CLASS" # The class object is defined within the layer object. You can define as
# many classes as you need (well, there are limits as with layers, but it's
# senseless to define more than ten on a "normal" layer. There are
# situations, however, where you might have to do it.)
CLASS
NAME 'States'
EXPRESSION 'land' # There are styles in a class, just like there are classes in a layer,
# just like there are layers in a map. You can define multiple styles in
# a class just as you can define multiple classes in a layer and multiple
# layers in a map.
STYLE
COLOR 232 232 232
END
END
END # States polygon layer ends here # In addition to vector data (shapefiles are vector data), MapServer supports
# a host of raster formats. In GIS world, one of the most common raster
# formats is GeoTIFF, a TIFF image with geospatial headers. MapServer also
# supports JPEG, PNG, GIF, and other common formats. Other raster formats
# supported by MapServer include ESRI Arc/Info grid, HDF and HDF-EOS, NetCDF,
# Generic raster binaries, OGC Web Map Service (WMS) layers, etc. Pretty much
# any raster format you can think of is probably supported, thanks to the
# impressive Geospatial Data Abstraction Library (GDAL, pronounced "GOODALL"
# or GOODLE?). More information on GDAL is available at http://www.gdal.org.
#
# MapServer 4.x can read and display bitmapped (like GIFs), RGB/A (true
# color), and multispectral (images with more than 3 bands, like raw LandSat
# images) rasters.
LAYER # MODIS raster layer begins here
NAME modis
DATA "raster/mod09a12003161_ugl_ll_8bit.tif"
STATUS OFF
TYPE RASTER
PROCESSING "BANDS=1,2,3"
OFFSITE 71 74 65 PROJECTION
"init=epsg:4326"
END
END # MODIS raster layer ends here LAYER # States line layer begins here
NAME states_line
DATA states_ugl
STATUS OFF
TYPE LINE PROJECTION
"init=epsg:4326"
END CLASSITEM "CLASS"
CLASS
NAME 'State Boundary'
EXPRESSION 'land'
STYLE
SYMBOL 'line5'
COLOR 64 64 64
SIZE 1
END
END
END # States line layer ends here LAYER # States label layer begins here
NAME states_label
DATA states_ugl
STATUS OFF
TYPE POLYGON PROJECTION
"init=epsg:4326"
END CLASSITEM "CLASS" # Just like CLASSITEM, LABELITEM defines the database attribute that you
# will be using to draw labels. In this case, the values of the attribute
# "STATE" will be used to label the states polygons.
LABELITEM "STATE"
CLASS
EXPRESSION 'land'
STYLE
COLOR -1 -1 -1
END # There can be labels in a class, just like there are classes in a layer,
# just like there are layers in a map. You can define multiple labels in
# a class just as you can define multiple classes in a layer and multiple
# layers in a map.
# MapServer has a very flexible labeling system. With that flexibility
# comes complexity, specially when using truetype fonts. Please read
# through the LABEL section of the MapServer map file documentation at
# http://www.mapserver.org/mapfile for more information.
LABEL
COLOR 132 31 31
#SHADOWCOLOR 218 218 218
#SHADOWSIZE 2 2
TYPE TRUETYPE
FONT arial-bold
SIZE 12
ANTIALIAS TRUE
POSITION CL
PARTIALS FALSE
MINDISTANCE 300
BUFFER 4
END # end of label
END # end of class
END # States label layer ends here
# End of LAYER DEFINITIONS -------------------------------
DEBUG 5
CONFIG "MS_ERRORFILE" "logs\ms.log"
END # All map files must come to an end just as all other things must come to...
在 IIS 中创建站点 Example1.6，端口为8016，应用程序池为 Example1.6
设置应用程序池对 apps/Example1.6/logs 文件夹的读写权限
在cmd中输入：icacls "E:\SvnWorkspace\LY_WEB_GIS\branches\Documents\ms4w-mapserver-for-wimdows\release-1911-x64-gdal-2-3-3-mapserver-7-2-1\apps\Example1.6\logs" /grant "IIS AppPool\Example1.6":(OI)(CI)RW
在浏览器中打开：http://localhost:8016/mapserv?map=../apps/Example1.6/example1_6.map&layer=states_polygon&layer=modis&layer=states_line&layer=states_label&mode=map
四、EXTENT的改变
查看mapfile（example1_6.map）文件后，首先，你会发现最明显的改变是 MAP 标签下面的 EXTENT 标签的数据。
EXTENT 表示当前数据文件的显示范围。现在的显示方为值如下：
EXTENT 201621.496941 -294488.285333 1425518.020722 498254.511514 #Example1.5 中是：EXTENT -97.238976 41.619778 -82.122902 49.385620
为什么会发生这样的改变呢，应为我们修改了MapServer 的输出坐标系，即添加了 PROJECTION 对象。
EXTENT对象的输出单位必须与 MapServer 中的输出坐标系一致。
先前的坐标系是经纬度。现在 PROJECTION 设置为：
# The projection object is typically used within the map and the layer
# objects. You only define it once within the map object and this definition
# becomes your output projection--MapServer will render your maps in this
# projection. You also use the projection object within the layer object to
# define your input projection. Your layers can be in different
# projections--MapServer will reproject them into your output projection.
# If no projection is defined within the layer object, MapServer assumes
# your input projection is the same as your output projection. This is not
# a required object unless you're creating a map file that supports one of
# the OGC interoperability web services specifications (WMS/WFS/WCS).
#
# This is the output PROJECTION definition ------
PROJECTION
# Projection parameters can be defined in two ways...
# This is the traditional PROJ.4 definition of Lambert Azimuthal Equal-Area
# projection for the Continental U.S.
"proj=laea"
"ellps=clrk66"
"lat_0=45"
"lon_0=-100" # Alternatively, you can specify an EPSG code.
# This is the EPSG code for Lambert Azimuthal Equal-Area
# projection for the U.S.
#
# "init=epsg:2163"
END # End of the output Projection definition ---
现在的 PROJECTION 设置为：Lambert Azimuthal Equal-Area，其单位为米，所以我们现在的范围 EXTENT 也要设置为米。
可以通过 ArcView、PROJ4 的 cs2cs 或其他GIS包做转换。下面的命令可用于重新投影原始范围值：
#第一步
#在cmd中输入：cd /d E:\SvnWorkspace\LY_WEB_GIS\branches\Documents\ms4w-mapserver-for-wimdows\release-1911-x64-gdal-2-3-3-mapserver-7-2-1\apps\tutorial\data
#在cmd中输入：ogrinfo -ro -al -so states_ugl.shp
#获取到states_ugl.shp 的范围信息：Extent: (-97.238976, 41.619778) - (-82.122902, 49.385620)。 Extent的格式为：<Lower Left X> <Lower Left Y> <Upper Right X> <Upper Right Y> #然后在cmd中输入下面的命令，回车 cs2cs +proj=latlong +datum=WGS84 +to +proj=laea +ellps=clrk66 +lat_0=45 +lon_0=-100 #执行当前计算转换，是在数据命令后，在输出原始范围的西南坐标值。即左下角坐标值，用空格分割开 -97.238976 41.619778 #回车后得到三个值，分别为：西南方向 X、Y、单位精度，其中第三个参数可以忽略。 230147.11 -371641.81 0.00 #接着再输入东北方向坐标参数 -82.122902 49.385620 #得到东北方向的转换输出范围： 1285308.08 632638.93 0.00 #所以转换后的EXTENT值为：
EXTENT 230147.11 -371641.81 1285308.08 632638.93 #转换完毕 #但是原始官网mapfile文件中给出的 EXTENT 值与计算值不符合。这是为什么呢？ EXTENT 201621.496941 -294488.285333 1425518.020722 498254.511514 # LAEA 原始官网mapfile中的数据 #因为地图在数据范围中并不居中，你可以适当的增加其范围，加以调整使其居中。官网案例是通过ArcView获取的。
当使用自己计算的范围时和官网通过ArcView修改后的范围，其显示为分别如下：
对比会发现，官网给定的做了相关边距接线的调整。
五、后记
在做本样例中，对MapServer又有了新的认识：
- 可以自定义投影坐标系的输出类型。
- PROJECTION中是如何通过PROJ4关键词参数定义输出坐标系的。
- PROJECTION是如何EPSG文件。
- EPSG文件到底是个什么东西：http://www.epsg.org/
- EPSG文件也可以自定义其目录位置。
- PROJ4中cs2cs命令的使用
MAP
CONFIG "PROJ_LIB" "/usr/share/proj/" #UNIX的绝对路径，如果是未定义，则按照安装MapServer中的 E:\SvnWorkspace\LY_WEB_GIS\branches\Documents\ms4w-mapserver-for-wimdows\release-1911-x64-gdal-2-3-3-mapserver-7-2-1\bin\proj\SHARE 路径查找（个人理解）
PROJECTION
"init=epsg:3857"
END # PROJECTION
...
后面还想写一篇关于关于PROJ4坐标转换的文章。一部一部学习。