Global Mapper v25.0

Create a jgw without an Export?

MCSQRD
MCSQRD Global Mapper User
edited February 2009 in Technical Support
I rectified a .jpg using GM. Is there a way to write a .jgw and .prj for .jpg without exporting the .jpg?

Comments

  • global_mapper
    global_mapper Administrator
    edited March 2008
    You would have to export a new JPG file because without that the JGW file based on the rectification would be meaningless against the original JPG file. A JGW file does not contain a set of control points, it just lists a top left corner and a pixel size, so unless your rectification was just a 2 point linear one, a world file would not be sufficient to describe the transformation needed without exporting an entirely new JPG file with the rectification applied to it.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • MCSQRD
    MCSQRD Global Mapper User
    edited March 2008
    I would say I am georeferencing the .jpg and not rectifying it. I have always thought when you rectify the image you actually change the pixels. I just want to georeference the existing pixels. Coming from the ArcGIS World it is possible to georeference an image and just assign a world file with out rectifying the .jpg. And I was looking for something similar in GM.
  • global_mapper
    global_mapper Administrator
    edited March 2008
    Whatever you call it, you are providing positioning information for at least 2 locations on your map so that it can be properly positioned. In the case of only providing 2 locations, then you could create a world file for the file that would accurately reflect the transformation, but in most cases if you are supplying 3 or more points a world file could not accurately reflect that information without completely regenerating the file.

    If you are only supplying 2 points, what I could do is add an option to the File menu on the rectification dialog to allow saving a world file based on the supplied control points. I would only allow this option to be used (or at least strongly warn the user against it) if more than 2 points were supplied defining a non-linear transformation.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • MCSQRD
    MCSQRD Global Mapper User
    edited March 2008
    ESRI Defines a World File in the following URL
    Technical Articles - ESRI Support

    I have always used three or more locations when referencing an image. That would be really cool to have the option to just create the world file from your File Menu in the rectification dialog. We are finding GM very useful and can work around it by Exporting the Image and checking Create World File and Projection File but it would be cool if we could just create them from the rectifier.
    Cheers
    Brett McMahon
    Newmont Mining Corporation
    Nevada District Exploration
  • global_mapper
    global_mapper Administrator
    edited March 2008
    Brett,

    If you are using 3 or more points to reference an image an then saving a world file and using that for positioning, you are likely losing information. Technically a world file can support all of the information from 3 control points if the rotation parameters are also used, but as many software applications can't handle those Global Mapper never writes out rotation values to a world file (it can of course handle them properly on import), so for most purposes a world file is only considered useful for a linear coordinate transformation definition.

    I can add the specified File menu command, but keep in mind that you will be losing information with this method vs actually saving out a new JPG file with a world file. The errors at each control point are the same as if you went to the Options menu on the rectification dialog and set the rectification method to 'Linear'. The errors can be significant in some cases, but may be livable in others. You would have to make that decision.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • global_mapper
    global_mapper Administrator
    edited March 2008
    Brett,

    I have gone ahead and added a new option to save a world file from the File menu on the rectification dialog. I have placed a new build at http://www.globalmapper.com/global_mapper9.zip with the change for you to try. Simply download that file and extract the contents into your existing v9.xx installation folder to give it a try.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • mikemurphy72
    mikemurphy72 Global Mapper User
    edited February 2009
    For those users who export to applications which are capable of displaying non-linear images, which have been georeferenced with a second or third-order polynomial transformation, could you add the capability of exporting the appropriate worldfile rather than discarding the additional referencing information? I am referring to the Export Raster function in GM.

    Thanks
  • global_mapper
    global_mapper Administrator
    edited February 2009
    Global Mapper actually applies any non-linear rectification on export so that the new image is then linear. If you want to save the original control points used to generate a non-linear transformation you can do so by opening the Control Center, right clicking on the layer, selecting the Modify Layer Position option, then using a File menu command to save out the control points.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com