实验二 全色影像和矢量叠加显示
[实验目的]：以全色（SPOT）影像数据为例，介绍基本处理、影像显示、对比度增强、ENVI的基本操作以及一些注意问题。本实验的目的还在于介绍ENVI的基本概念和该软件的主要特征。 [实验内容]：
1. 遥感图像增强显示的相关操作； 2.图像叠加显示的基本操作； [实验准备]：
数据：文件夹 envidata/enfidavi
文件 描述 enfidavi.bil Enfidaville, Tunisia 地区的SPOT的全色影像。 enfidavi.hdr ENVI 相应的头文件 enfidavi.dsc GeoSpot 体描述文件 enfidavi.rep GeoSpot 报表文件 (REP/B: GEOSPOT 结构) enfidavi.rsc GeoSpot 栅格源描述文件 dxf.txt DXF DXF 编码描述文件 alti.dxf Spot 高程 DXF 矢量文件 energy.dxf Oil or Gas Pipeline DXF file hydro.dxf Hydrology DXF file industry.dxf Industrial Areas DXF file physio.dxf 地形 DXF 矢量文件 popu.dxf Urban Features (Population Centers) DXF file transpor.dxf Transportation Networks DXF file copyrite.txt Data Copyright Notice
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[实验步骤]： 一、对比度拉伸 1．定制拉伸 2．交互式拉伸 拉伸参数设置
When images are loaded into the Main Image window, a 2% linear contrast stretch is applied by default. To change the default, stretch select File / Preferences from the ENVI main menu. In the System Preferences dialog, click the Display Defaults tab. Click the Display Default Stretch button menu and select the stretch type. 二、彩色制图，将灰阶影像进行快速分割（color slicing）
Image window: Tools → Color Mapping → ENVI Color Tables 滑块设置和选择预定义颜色表 三、像素定位器
Image window: Tools → Pixel Locator
The Pixel Locator dialog allows exact positioning of the cursor and displays the screen and data values of the selected pixel. 四、显示光标位置处的地理坐标
Image window: Tools → Cursor Location/Value 五、交互式滤波处理
Image window: Enhance → Filter
打开两个窗口分别使用不同的滤波处理，用动态链接比较两者差异。
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ENVI gives you the ability to apply several different pre-defined or user-defined filters to a display. 六、查看GeoSpot地图信息
In the Available Bands List, right click on the Map Info icon under the filename and select Edit Map Information from the shortcut menu. 七、打开并叠加DXF矢量文件
导入，参数设置，显示
1. From the ENVI main menu, select File → Open Vector File → DXF. A standard file selection dialog called Enter DXF Filenames appears.
2. In the file selection dialog, navigate to enfidavi directory. If it is not already set, set the Files of type: field to *.dxf and select all of the files with the .dxf extension. Click Open at the bottom of the file selection dialog on Windows to open the Import DXF File Parameters dialog.
3. Midway down the Import DXF File Parameters dialog is the selection list of projections. In the Native File Projection list, click on UTM. This field refers to the map units that the imported vector data is in.
4. Click the Datum button to bring up the Select Geographic Datum dialog. Highlight the Mexico (NAD27) datum in the list and click OK.
5. In the Import DXF File Parameters dialog enter the UTM Zone as 32 and click the N radio button.
6. Click OK to load the DXF files and have them converted to .evf (ENVI Vector Files).
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7. The Available Vectors List dialog appears. Click on the Select All Layers button. Next, click on the Load Selected button. A Load Vector dialog appears which lists all of the available displays.
8. Select Display #1 from the list. The #1 Vector Parameters dialog appears showing the named vector layers.
9. Click on one of the layer names in the #1 Vector Parameters dialog. In the Main Image display click and drag the left mouse button to move the cursor in the image and observe map coordinates for the selected vectors in the #1 Vector Parameters dialog. 八、基本地图制图
1．添加公里网：Overlay → Grid Lines
2．添加地图图例：Overlay → Annotation.点、线、面、注记。 3．保存和恢复注记。
Note：If you do not save your annotation in a file, it will be lost when you close the Annotation dialog (you will be prompted to save the annotation if you close without first saving). 九、 保存和输出图像
File → Save Image As → Image File（TIFF/GeoTIFF） End the ENVI Session
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