MapServer6.4.1教程学习--添加栅格图层(1-5)

示例1.5

添加栅格图层

（http://www.mapserver.org/tutorial/example1-5.html#example1-5）

除了支持矢量数据（点，线，多边形和注记）外，MapServer也能显示栅格数据。通过使用GDAL库，MapServer支持多种栅格格式的输入输出。然而4.x版本以下的栅格输入只限定于单图层，灰度或索引图。当前MapServer版本支持RGB和多光谱（多图层）影像。这个例子展示了采用多光谱数据时如何选择层去显示。

注意：当使用RGB和多光谱数据时会有显示的性能损失。

由于MapServer 5.x使用AGG或GD 2.0.x生成输出图像，它也支持RGB（24位或真彩色）输出。所以，在支持8位（索引色或灰度）PNG8，你也可以使用PNG（真彩色）输出。此例使用的是PNG作为IMAGETYPE。

注意：当使用RGB输入时，使用PNG相比PNG8输出的时候性能会有显著下降

MapServer实际上是可以使用GDAL输出图你的，但那是另一个话题。如果你想了解更多，请看mapfile参考手册里面的OUTPUTFORMAT对象。

MapFile结构

下面是示例1-5的mapfile文件：

#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     PNG

  EXTENT        -97.238976 41.619778 -82.122902 49.385620

  SIZE          400 300

  SHAPEPATH     "../data"

  IMAGECOLOR    255 255 255

  FONTSET       "../fonts/fonts.list"

  SYMBOLSET     "../symbols/symbols35.sym"

 

  # Layer objects are defined beneath the mapobject.  You need at least one

          # layer defined in your map filebefore you can display a map...  You can

  # define as many layers as you'd likealthough 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 applicationto need more than 100 layers in

  # your application.

  #

  # Start of LAYER DEFINITIONS---------------------------------------------

  LAYER # States polygon layer begins here

    NAME        states

    DATA        states_ugl

    STATUS      OFF

    TYPE        POLYGON

 

    # CLASSITEM defines the non-spatialattribute 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 foreach data format).  In this

    # example the shapefile states_ugl has anassociated database

    # (states_ugl.dbf) that contains anattribute called "CLASS".  Youwill be

    # using two values in the CLASS attributeto separate the classes (also

    #called themes) used in this layer--land and water.  CLASSITEM is used in

    # association with the EXPRESSION parameterin the CLASS object.  See below.

    CLASSITEM   "CLASS"

 

    # The class object is defined within thelayer object.  You can define as

    # many classes as you need (well, there arelimits as with layers, but it's

    # senseless to define more than ten on a"normal" layer.  There are

    # situations, however, where you might haveto do it.)

    CLASS

      NAME 'States'

      EXPRESSION 'land'

 

      # There are styles in a class, just likethere are classes in a layer,

      # just like there are layers in amap.  You can define multiple styles in

      # a class just as you can define multipleclasses 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 arevector data), MapServer supports

  # a host of raster formats.  In GIS world, one of the most common raster

  # formats is GeoTIFF, a TIFF image withgeospatial headers.  MapServer also

  # supports JPEG, PNG, GIF, and other commonformats.  Other raster formats

  # supported by MapServer include ESRIArc/Info grid, HDF and HDF-EOS, NetCDF,

  # Generic raster binaries, OGC Web MapService (WMS) layers, etc.  Pretty much

  # any raster format you can think of isprobably supported, thanks to the

  # impressive Geospatial Data AbstractionLibrary (GDAL, pronounced "GOODALL"

  # or GOODLE?).  More information on GDAL is available athttp://www.gdal.org.

  #

  # MapServer 4.x can read and displaybitmapped (like GIFs), RGB/A (true

  # color), and multispectral (images with morethan 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

  END # MODIS raster layer ends here

 

  LAYER # States line layer begins here

    NAME        states_line

    DATA        states_ugl

    STATUS      OFF

    TYPE        LINE

 

    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

 

  # Labels can be defined in its ownlayer.  This is useful if, say, you want

  # to label a polygon layer that's covered byanother layer.  By keeping the

  # label separate from the polygon and placingit near the bottom of the map

  # file (so its drawn on, or near the, top),you can still see the label even

  # though you might not be able to see thepolygon.  It is also a good

  # alternate to point symbols.

  #

  # A label layer is actually defined withANNOTATION type (This is derived from

  # points, Node IDs for lines, or polygonIDs).

  LAYER # States label layer begins here

    NAME        states_label

    DATA        states_ugl

    STATUS      OFF

    TYPE        ANNOTATION

 

    CLASSITEM   "CLASS"

 

    # Just like CLASSITEM, LABELITEM definesthe database attribute that you

    # will be using to draw labels.  In this case, the values of the attribute

    # "STATE" will be used to labelthe states polygons.

    LABELITEM   "STATE"

 

    CLASS

      EXPRESSION 'land'

      STYLE

        COLOR      -1 -1 -1

      END

 

      # There can be labels in a class, justlike there are classes in a layer,

      # just like there are layers in amap.  You can define multiple labels in

      # a class just as you can define multipleclasses in a layer and multiple

      # layers in a map.

      # MapServer has a very flexible labelingsystem.  With that flexibility

      # comes complexity, specially when usingtruetype fonts.  Please read

      # through the LABEL section of theMapServer map file documentation at

      # http://www.mapserver.org/mapfile formore information.

      LABEL

        COLOR 132 31 31

        #SHADOWCOLOR 218 218 218 # deprecated, useSTYLE and GEOMTRANSFORM

        #SHADOWSIZE 2 2          # deprecated, use STYLE andGEOMTRANSFORM

        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-------------------------------

 

END# All map files must come to an end just as all other things must come to.

Mapfile的对象结构如下：

MAP

LAYER#1-------------LAYER #2----|----LAYER #3--------LAYER #4

(states_poly)           (modis)       (states_line)   (states_label)

|                                     |               |

(land)CLASS-|-CLASS (water)                      |-CLASS         |-CLASS

|     |                                     |               |

STYLE-|     |-STYLE                               |-STYLE   STYLE-|-LABEL

当你看到这个mapfile文件，你会发现在多边形州图层后面（下面）添加了一个新的LAYER对象。为什么？MapServer是按反序显示图层的：后进先出（LIFO）.mapfile文件中定义的第一个图层会在地图最底层绘制。

所以，如果我们绘制了多边形州图层，它将位于最低层。如果我们在它上面绘制栅格图层，我们将看不到它。这就是为什么第一个图层的STATUS值要设置为OFF。LINE图层定义在栅格图层后面，所以它绘制在栅格图层上面（你可以看到它）。这也是为什么我们将线形州图层从多边形州图层分离的原因。当然标注是绘制在所有图层之上。

MapServer能够基于其他图层的状态自动打开或关闭某一个图层（比如当栅格图层打开的时候你想关闭多边形州图层）。这个是通过使用REQUIRES参数来实现的。一旦开始创建你自己的MapServer应用的时候你要记住这一点。

参数

让我们看看这个mapfile文件中的新参数。

IMAGETYPE

         PNG是一种24位或真颜色版本的PNG格式。你也可以试着将这个值改为PNG8。无论使用何种格式注意生成图像的时间。当在真彩色和索引色之间选择时，需要考虑生成图像的时间。

SYMBOLSET

指向符号定义文件路径。文件中的符号被CLASS对象内的SYMBOL参数引用。其实此刻并不是真的需要但是我想在这里抛出空上。请参考Cartographic Symbol Reference 获取更多信息。

DATA raster/mod09a12003161_ugl_ll_8bit.tif

在新添加的LAYER对象中，DATA参数指向一幅GeoTIFF图像。正如支持多格式矢量数据，MapServer也支持多种栅格文件格式。这种支持是通过使用GDAL库来获取的。请阅读Raster Data Reference.获取MapServer支持的不同栅格格式信息和MapServer中栅格用法的一般讨论。

TYPE RASTER

矢量数据TYPT值为POLYGON,LINE和POINT，而用ANNOTATION来表示标注。相反，使用栅格数据（图像）时，我们使用RASTER给参数TYPE赋值。

PROCESSING “BANDS=1,2,3”

LAYER对象参数是在MapServer4.x中添加的。PROCESSING关键字有很多值，但是这里我们用它来指定多光谱数据中哪些波段显示。这个字符串类型的值会传给GDAL库。

OFFSITE

 这个参数告诉MapServer哪个像素值需要作为背景（或无效值）去渲染。你可以用图像处理或图像操作程序来获取这个像素值（如Imagine,Photoshop,Gimp）.

RGB vs 索引图

为了对比用RGB图像和索引图生成地图的速度，需要将示例的mapfile中的以下几行：

DATA"raster/mod09a12003161_ugl_ll_8bit.tif"

STATUSDEFAULT

TYPERASTER

PROCESSING"BANDS=1,2,3"

OFFSITE71 74 65

替换为

DATA"raster/mod09a12003161_ugl_ll_idxa.tif"

STATUSDEFAULT

TYPERASTER

OFFSITE70 74 66

再一次，将IMAGETYPE从PNG改变为PNG8。

 

 

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