IDL批量提取图像DN值出错，求助！谢谢！

Eric.Yang

大家好！我想用idl通过经纬度批量提取遥感图像的dn值，参考了http://blog.sina.com.cn/s/blog_942ff76e0102v406.html的帖子，但我在批量处理的时候，总是出现这个错误：Object reference type required in this context: MAPINFO.请各位大神帮忙看一下，问题出在哪？请指导一下，谢谢！

1. pro Extrat_TIFDN3
   
2. Compile_opt IDL2
   
3. ENVI,/RESTORE_BASE_SAVE_FILES
   
4. ENVI_BATCH_INIT
   
5. 
   
6. directory = 'E:\Data\modis\tif\'
   
7. product = '*AOT.tif'
   
8. files = file_search(directory + product)
   
9. ;beijing
   
10. longitude=116.381
    
11. latitude=39.977
    
12. for i=0,n_elements(files)-1 do begin
    
13. ;Convert to the Projection as same as the Imput Image
    
14. ENVI_OPEN_FILE,files[i], r_fid=fid ;1. Retrieve the Pojection Info from Input Image
    
15. ENVI_FILE_QUERY, fid, dims=dims;some parameters will be used to get data
    
16. ProjInfo=ENVI_GET_PROJECTION(fid=fid)
    
17. OriProj=ENVI_PROJ_CREATE(/geographic) ;2. Original projection of Lon/Lat
    
18. ENVI_CONVERT_PROJECTION_COORDINATES,longitude,latitude, OriProj,otX, otY, ProjInfo ;3. Process of Convert
    
19. 
    
20. ;;Extract the Col & Row for the input Geoinfo
    
21. mapinfo=ENVI_GET_MAP_INFO(fid=fid) ;1. Geolocation of Upper Left Point (0, 0) of the Input Image
    
22. print,mapinfo
    
23. <FONT color=red>ULlon=mapinfo.mc(2) ：出错！！！  Object reference type required in this context: MAPINFO.</FONT>
    
24. print,ULlon
    
25. ULlat=mapinfo.mc(3)
    
26. Xsize=mapinfo.PS(0) ;2. X/Y Size of the Input Image
    
27. Ysize=mapinfo.PS(1)
    
28. Row=(otX-ULlon)/Xsize ;3. Calculate the Number of Col & Row
    
29. Coll=(otY-ULlat)/Ysize
    
30. Row=fix(abs(Row)) ;Subscript directly from 0
    
31. Coll=fix(abs(coll))
    
32. 
    
33. tiff=Read_Tiff(files[i], GeoTIFF=GeoVar)
    
34. NC_DN=tiff(Row, Coll)
    
35. print,NC_DN
    
36. endfor
    
37. 
    
38. envi_batch_exit
    
39. print,'job done!'
    
40. 
    
41. end

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