-Rectifying a Geotiff

eagleeyeeagleeye Global Mapper UserPosts: 3
Hi
I downloaded GM10 Trial and I loaded a GeoTiff. In My case
the UTM was set to 47N. Because thats where the image was
taken.. I used Modified Everest in my import ..

The Latitude of a known point seems to be correct
its 4.xxx N but the Longitude seems to be off by 3 degrees
currently its 97.xxx east it should be 101.xxxx East.

So the lat is 4.xxx N and the long is 97.xxx E
How do you ask GM10 to ensure that the same coordinates
is 4.xxx N and 101.XXX E

is there a way to 'offset' the data as the geotiff is loaded?

I found a text file that has the following contents.

Erdas Imagine File Information
SPOT-5
Resolution : 2.5
Block Width : 64
Block Height : 64
Pixel Depth :Unsigned 8-bit
Compression Type : None
Projection Information :
Projection Zone : 0
Spheroid Name : Modified Everest
Georeferenced to : RSO
Map Information :
Upper Left center X : 361083.750000
Upper Left center Y : 512521.250000
Lower Right center X: 391453.750000
Lower Right center Y: 482256.250000
Pixel X size : 2.500000
Pixel Y size : 2.500000

Is there a way to make use of this info?

There is also a TFW file that has the following contents.
2.5000000000000000
0.0
0.0
-2.5000000000000000
361083.75000000000
512521.25000000000

Hopefully there is an easy way to do this.

Eagleeye

Comments

  • eagleeyeeagleeye Global Mapper User Posts: 3
    edited September 2008
    Hi
    I guess I will answer my own question. After playing with the options, I noted
    RSO as being listed so I selected it and meaningful values appeared in the import
    form.. now the values are 'correct' but it seems my GPS tracks become
    incurrate in parts of the geo tiff, going off 600 feet..

    I guess its because my GPS tracks are WGS 84 (Garmin ) and not
    RSO?

    Eagleeye
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited September 2008
    I think that your remaining shift is a datum issue. All that was listed was that the ellipsoid used by your data set was 'Modified Everest'. Unfortunately a true datum conversion requires an ellipsoid and some set of transformation parameters to get that to WGS84 and other datums accurately. Do you know more about what actual datum your data might be using? There are several Everest-based datums in Global Mapper, including several of the India datums, Kertau, and Timbalai.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • eagleeyeeagleeye Global Mapper User Posts: 3
    edited September 2008
    Hi
    thats all the info I have.. It would be nice to have a feature
    in GM that allows the re-calibration of a geotiff to actual Parameters.

    For example you lay a track over the Geotiff and then you tell
    GM where that Waypoint is suppose to be OR you allow the
    track to be dragged over the Geotiff until it is positioned correctly
    and save the changes..

    I loaded the same Geotiff into Oziexplorer but
    as a normal Jpeg file and calibrated it manually because I happened to
    have the tracks across 50% of the Geotiff. The result is
    very usable -Although I know that the bitmap is a bit off!

    Google Earth does not have a photo of this area so I cannot
    rely on GE wayppoints but only my own GPS tracks.

    Another option will be to allow the conversion of GPS tracks
    into the SAME projection as the loaded Geotiff as the tracks
    are being loaded.

    I will trial and error on all the Everest formats and see what happens

    Eagleeye
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited September 2008
    You can do exactly what you are describing in Global Mapper either by loading your imagery using the File->Rectify Imagery menu command, or by opening the Control Center, right-clicking on an existing layer, then selecting the option to reposition the layer.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
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