两幅TM遥感图像需要几何校正
在erdas中，TM影像的配准需要DEM信息，
Elevation Source: Select the source of the elevation information for this image.
Include zeros when building statistics for the elevation file if there are actual zero elevations (sea level) in the file. Failure to do so will result in those pixels being masked (having a value of zero) in the output image.
Use: Select whether to use DEM data or a constant value as the elevation. When the terrain of the rectified area is relatively flat, a constant elevation could be sufficient for an accurate orthorectification.
File Activate this radio button to obtain the elevation data from a DEM file.
Constant Activate this radio button to use a constant value as the elevation information.
Elevation File: Enter the name of a file that contains elevation data. Click the Open icon 
icon to open the File Selector dialog. This option displays when the File radio button is activated.
Elevation value: Enter the constant elevation value. This option displays when the Constant radio button is activated.
Elevation Units: Click this dropdown list to select the elevation units used by the DEM or for the constant value.
在envi中，似乎更容易一些，只需要选合适的控制点
在arcgis中，也可以，而且当时可以看到校正的效果
PS：一般是用高分辨率的来校正低分辨率的，那么高分辨率的几何校正就需要地面控制点了
几何校正的范围不要太大
做分析前的预处理不能忽略，尤其是投影坐标问题，如果处理不好，会为后续工作带来很大的麻烦
