LOLA LBL Corrections - fermigas/ltvt GitHub Wiki
Examples... Digital topography... Sources of Planetary DEM Data...
In the early releases of LDEM_4.LBL and LDEM_16.LBL, the "OFFSET" of the raw data values was incorrectly listed as "1728216." (meters). This was corrected to "1737400." on 22 Mar 2010. However the new *.LBL files contain new errors making the LOLA *.IMG files unreadable by releases of LTVT prior to 23 Mar 2010, and causing the polar stereographic DEM's to display with an incorrect scale. New *.LBL files were uploaded twice on 25 Mar 2010, the second appearing close to correct, however containing a change in MAP_SCALE units not anticipated by LTVT.
*Correcting scale of LOLA polar stereographic .LBL files dated 22 Mar 2010:
- Open the *.LBL file with a text editor, such as Notepad or WordPad
- Find the line towards the end of the file the line "MAP_SCALE = 100 "
- Change the number from "100" to the correct scale (as indicated in the earlier descriptive text), which can vary from 20 to 400 (meters).
- Also look for the line that says "CENTER_LATITUDE". The number should be either "90 " for north polar projections, or "-90 " for south polar projections. If the "-" sign for south polar projections has been omitted, it needs to be inserted.
- Save the file and exit the text editor.
*Making LOLA .LBL files dated 22 Mar 2010: readable by earlier versions of LTVT
(this manual editing is not necessary for LTVT_v0_21_3x.exe released 23 Mar 2010 or later)
- Open the *.LBL file with a text editor, such as Notepad or WordPad
- Find the line under "OBJECT = UNCOMPRESSED_FILE" saying something like FILE_NAME = "LDEM_64.IMG".
- Change the word FILE_NAME to ^IMAGE.
- In the polar DEM's, find the line "LINE_SAMPLES" (under "OBJECT = IMAGE). Correct the "LINE_SAMPLES" number so that it equals the one listed on the "LINES" line preceding the "LINE_SAMPLES" line (do not make this correction to the simple cylindrical global DEM's). Also correct the "MAP_SCALE" of the polar DEM's as described above.
- Save the file and exit the text editor.
*Making polar LOLA .LBL files dated 25 Mar 2010: readable by earlier versions of LTVT
(this manual editing is not necessary for LTVT_v0_21_3x.exe released 25 Mar 2010 or later)
- Open the *.LBL file with a text editor, such as Notepad or WordPad
- Find the line towards the end of the file the line "MAP_SCALE = nnn <m/pixel>" where "nnn" is a number.
- Change <m/pixel> to .
- Save the file and exit the text editor.
This page has been edited 3 times. The last modification was made by - 
JimMosher on Sep 20, 2010 2:17 pm