ii. Geometric Correction

10. Click on RASTER Menu of the Viewer Window
11. Click on GEOMETRIC CORRECTION. Then it will display the SET GEOMETRIC MODEL Window as shown below

12. Select POLYNOMIAL as the option for GEOMETRIC MODEL from the above displayed list of model
13. Click on OK. Then it will display the POLYNOMIAL MODEL PROPERITY Window as shown below

14. Click on the PROJECTION tab. Then observe that the displayed window looks like above. As per the selection of the option it will display. By default this will be on PARAMETERS Tab
15. Click on the ADD/CHANGE PROJECTION option. Then it will display the PROJECTION CHOOSER Window as shown below

16. Click on the CUSTOM Tab option, of the Projection Chooser Window. By default this will be on Standard Tab
17. Click on PROJECTION TYPE list box
18. Select GEOGRAPHIC (LAT/LON) as the option for the Projection Type from the displayed list.
19. Click on the SPHERIOD NAME list box
20. Select EVEREST 1956 as the option for Spheroid
21. Click on the DATUM NAME list box
22. Select UNDEFINED as the option for Datum
23. Click on OK. Then it will be back to POLYNOMIAL PROPERITY Window
24. Click on SET PROJECTION FROM GCP TOOL option. Then it will display the GCP TOOL REFERENCE SETUP window displayed as shown below

25. Select KEYBOARD ONLY as the option for COLLECTION REFERENCE POINT FROM
26. Click on OK. Then it will display the REFERENCE MAP INFORMATION Window as shown below. In this window

It shows the Current Reference Map Projection as follows

Projection : Geographic (Lat/Lon)
Spheroid : Everest 1956
Datum : Undefined
Map Units : Degrees

27. Click on OK. Then it will open five windows as shown below

GCP Tool Window;

• Viewer 1 Window
• Viewer 2 Window it is also called Magnifier Window for Viewer 1 Window
• Polynomial Property Window
• Geo Correction Tool Window

28. 28. Click on APPLY on the Polynomial Property Window
29. Close the Viewer 2 Window or Magnifier Window
30. Activate the GCP TOOL Window by clicking on its Title Bar. In this GCP Tool Window

31. Click to turn off and on the automatic GCP editing mode.

32. GCPs. . Then the cursor will turn into a cross hair in the Viewer.

33. Then Click TOP LEFT CORNER of the Map. That will be taken as GCP Point 1
34. Activate the GCP TOOL Window and Enter the X REF and Y REF Values for the first GCP as the Geographic

Coordinates of the point
X REF : 77 30 ( Here type 77, after that leave one blank space and again type 30, then it will automatically convert into Decimal Degree values)
Y REF : 18 30 ( Here type 18, after that leave one blank space and again type 30, then it will automatically convert into Decimal Degree values)

35. Activate Viewer and Click at TOP RIGHT CORNER of the Map then this points will be GCP Point 2
36. Activate the GCP TOOL Window and Enter the X REF and Y REF Values for the first GCP as the Geographic

Coordinates of the point
X REF: 77 45 and Y REF: 18 30

37. Activate Viewer and Click at BOTTOM RIGHT CORNER of the Map then this points will be GCP Point 3
38. Activate the GCP TOOL Window and Enter the X REF and Y REF Values for the first GCP as the Geographic

Coordinates of the point
X REF: 77 45 and Y REF: 18 15

39. Activate Viewer and Click at BOTTOM LEFT CORNER of the Map then this points will be GCP Point 4
40. Activate the GCP TOOL Window and Enter the X REF and Y REF Values for the first GCP as the Geographic

Coordinates of the point
X REF: 77 30 and Y REF: 18 15

Then the GCP TOOL Window looks like

41. If you want to change the color for GCP points, Then select all the ROWS and block the COLOR Column, right click on COLOR Column and pickup required color for GCP Points.

42. Click on to solve the geometric model with control points
43. Activate the GEOCORRECTION TOOL Window

44. Click on to open the Resample dialog. From this dialog, you can choose the desired output file, resample method, and output information.. Then it will display the RESAMPLE Window as shown below

45. Type the OUTPUT File Name as RECT_MEDAK_56F11 and save this in the folder D:\ERDAS_Exercis_Files
46. Check the option for IGNORE ZEROS IN STATS
47. Click on OK. Wait for few Seconds to complete the process of sampling
48. Activate GCP Tool Window,
49. Click on SAVE AS option in the File Menu
50. Type the name as Medak_F11. The extension of this file is GCC
51. Click on OK
52. Close this window
53. Click on EXIT on the GCP Correction tool. And also Close all other windows which are opened during this process by selecting options NO as and when it will display

iii. Viewing the Rectified TopoSheet
54. Click on VIEWER Icon of the Main Tool Bar
55. Select Viewer type as CLASSIC VIEWER
56. Click OK to get a blank Viewer Window
57. Click on OPEN
58. Select RASTER LAYER option
59. Then Browse for the File RECT_MEDAK_56F11.IMG and select the same file
60. Click on OK to display on the viewer
61. Click on the RIGHT CLICK of the Mouse and Select FIT IMAGE TO WINDOW option to display the entire image on the screen.
62. Now observe that wherever you place the cursor the LAT/LON values of that point will be displayed.

Registration of Toposheet 56F12

By following the above procedure from step 1 to 62 Rectified the Medak TopoSheet 56F12. While rectification use the following LAT/LON Values.

Sno	Longitude	Latitude
1	77 30	18 15
2	77 45	18 15
3	77 45	18 00
4	77 30	18 00