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Problems with georeferencing pictures from Google Earth

soupssoups Global Mapper UserPosts: 8
edited July 2010 in Georeferencing Imagery Discussion
Hi, not sure if I'm doing this wrong. I use the Save option on Google Earth to save the current screen and choose to save it as the largest resolution it can support. I end up with a jpg. I load this jpg up in Global Mapper and it lets me do some georectification. I chose 9 points - the 4 corners, 4 mid side points and the centre point and left the other options to the default eg WGS84. The result is the picture displayed slightly skewed. We then measured some distances and checked lat lons between Global Mapper and Google Earth and do get discrepancies. I am using version 9 of Global Mapper.

Have anyone done this before and can tell me what I may be doing wrong?

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited August 2008
    There was a bug in v9 that sometimes caused rectification to not use the most accurate method available. I have placed a new build at http://www.globalmapper.com/global_mapper9.zip with this fixed 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
  • soupssoups Global Mapper User Posts: 8
    edited August 2008
    I'm afraid the new build did not work. I saved the current screen off Google Earth. Open it in Global Mapper. Supply 4 points (corners) to geo rectify. The result is a squashed picture (widescreen format rather than boxed).

    If I open the jpg without geo-rectifying, then the jpg opens in the correct dimensions.

    If it is of any help, I am capturing the town of Bedford in England at eye alt 3.21km.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited August 2008
    Ah, your problem is just what projection the data is viewed in. The default Geographic (lat/lon) projection will seem squashed if you are far from the equator. To fix this, simply go to the Projection tab of the Configuration dialog and change your projection to one more appropriate for your location, like British Grid or UTM.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • soupssoups Global Mapper User Posts: 8
    edited August 2008
    Aah that seem to resolve the squashiness problem by choosing UTM. The result is the picture of the correction dimensions but slightly rotated to the left. Is this normal?
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited August 2008
    Yes, different projections will display things differently. If your data is far from the center of a UTM zone, it will be slightly rotated. You might also try the British Grid projection as it may have less rotation in your area. To get no rotation, you might try a Transverse Mercator projection and set the Central Meridian and Origin Latitude to values in your map.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • FeralkiwiFeralkiwi Global Mapper User Posts: 1
    edited September 2008
    Hi Soaps

    I have spent some time setting up spreed sheet files to automaticly load and refferance google sat pics.

    Then Google changed the refferancing in their url address at the strat of this mounth.

    I have now reprogramed my spreed sheets.

    The new google address's contain xyz coordinats.

    http://khm0.google.co.nz/kh?v=30&hl=en&x=0&y=0&z=1&s=

    x starts at top left 180 west
    y start at top left at 85.*** north (a mercetor calculation result limit.)
    z is the zoom level (x and y are dependant on z)
    s with the "galileo" I don't know yet
    and the other s that appears in larger zooms, ? as well

    I scan around in google maps in the zoom level and area I require and then exstract the image address's from the Temp internet folder useing STG Cache Audit program.
    STG Cache Audit

    The attached files are www: OpenOffice.org - The Free and Open Productivity Suite spreed sheet and hopefuly an windows exel spreed sheet.

    First exstract the file address with STG Audit and export them to a .csv file.
    I set the custom filter in STG Audit to gretaer then and equal to "http://khm"; and less than "http://khn". This gives only the google image files.
    Load that file into a spreed sheet and sort out what files you want. You may need to use part of my file to first exstract the XYZ values to sort with.

    Then copy the result including the header line to sheet 3 of my spreed sheet.

    There are instructions on sheet one of my file from there

    Start with only one file to test with.

    The output is three files. A renamed copy of the original Google image 256x256 picels. The name is Z X Y from the original Google address.
    The second file is a world file.
    The third file is (I hope) a projection file.
    Open just the image (or images) file with Globalmapper and it should auto reffance with the other two files.

    There are auto loader programs out there but Google blocks your IP address for 24 hours after you load about 3-400 images. I did this at my local library and blocked all the Christchurch librarys form accessing any sat images. Whoops!


    Yours Owen
  • kaldenkalden Global Mapper User Posts: 41
    edited March 2010
    Yeah, I wouldn't recommend sniping google imagery data like this. They block your IP for a reason. It is a big TOS violation.

    Manually rectifying their medium res JPG output is one thing. Intercepting their raw image tiles is basically stealing
  • Ioannis.magIoannis.mag Global Mapper User Posts: 12Trusted User
    edited July 2010
    hm.. interesting approach to geo referencing a google earth image. What I do is set up GM and the GE lat/long lines at the same scale so in a sence I have a mesh of coordinates that I can vicually match manually to GM. It might not be the most accurate approach but if you bother to zoom in a lot. Still you are end up with the lat long line in the image, which unfortunately you cannot wipe out.
  • kfroesekfroese Geotechnical Engineer Posts: 186Trusted User
    edited July 2010
    I'm with kalden: this thread is essentially discussing a violation of the Google's Terms of Use.
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