Global Mapper Pro

locating palaeogeographic maps in GM

Nick Hardy
Nick Hardy Global Mapper User
edited June 2012 in Raster Data
Hi

I have some palaeogeographic maps that I would like to georeference - I know how to do this in a conventional way in the software, but this distorts the maps.

Is there a way of import an image file (jpg/tif etc) and then just rotate, stretch and locate the map to the desired location?

Thanks.

Comments

  • global_mapper
    global_mapper Administrator
    edited June 2012
    Actually rectification would be the way to do that most easily. What projection are you rectifying in? You want to try and match the original projection of the image being rectified, but if you don't know you might try something like UTM (with an appropriate zone) as it will not have much distortion, assuming your maps don't extend more than a few degrees longitudinally.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • Nick Hardy
    Nick Hardy Global Mapper User
    edited June 2012
    Thanks Mike.

    My projection is UTM28 WGS84 and I am working just off the Moroccan coast, but the palaeogeographic map goes up to northern Spain and across to Nova Scotia. It's a Jurassic reconstruction so the north Atlantic is very narrow at the time and Spain is in a different location as well so the point I have are just a narrow band also part of the coast - I have rectified using these but quite a bit of distortion in the distal parts of the map. I have tried putting in some dummy points in the distorted areas, but this is not working very well, hence my question about just bringing in the image and strectching, rotating and skewing the image (I assume that this is not available?).
  • global_mapper
    global_mapper Administrator
    edited June 2012
    Ah that would be much too large for UTM then. Perhaps Robinson would be a good choice. However it sounds like the real source of the distortion is the lack of control points spread across the map. You can just offset, scale, and rotate an image by right-clicking on it in the Control Center and select the Shift/Transform option. On the dialog that pops up one of the choices is to shift/rotate/scale the map. This might work for you if you don't have anything to base known control points off of.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • Ice Age Mark
    Ice Age Mark Global Mapper User Trusted User
    edited June 2012
    FWIW


    I've successfully rectified all sorts of different raster images of maps, even crooked scans of pages in textbooks, with GM over the years. The scale has ranged from a sketch map of some Anasazi stone stairways in Chaco Canyon (even going so far as to use the "nick points" of contours as some of my control points), to scanned portions of folded paper geologic maps, to global paleoclimatic and paleogeographic maps.


    My best results were usually achieved by avoiding manual rectification and reprojection of the raster image if at all possible. As Mike said, "scale, rotate, translate" is the way to go. This is the only way to position a "picture of a map" without distorting it. By doing it this way you can (sometimes), in a sense, rectify the raster image with only one common control point, or just visually.

    For more detail, just ask.


    Best of luck,


    Mark
  • vxon_kitt
    vxon_kitt Global Mapper User Trusted User
    edited June 2012
    I am also interested in knowing the process of rectifying an image with only a point and the scale and rotation. If you could be so kind, please let us know further details.

    Thanks a lot!

    Regards from Spain.
  • Nick Hardy
    Nick Hardy Global Mapper User
    edited June 2012
    Thanks Mark.

    I have used the scale, rotate, translate method as suggested - a bit fiddly but has worked well. Is there any way of using a "drag and drop" method? Or could this be an add on using some key combinations and the mouse?


    Thanks for all your help.

    Nick
  • Ice Age Mark
    Ice Age Mark Global Mapper User Trusted User
    edited June 2012
    Nick,


    Thanks for the thanks. "Fiddly" it is. It's possible that even with "drag and drop" you may have to "hone" your destination position a time or two. I ran into this in my surveying days. When I would translate a coordinate set a long distance, it would be close, but not exact, and I would have to translate a second time. I think it's truncation errors. If you can possibly get your map image converted to vector form using "Create areas for equal values", it's much easier to manipulate, and of course then you can edit and even "fudge" individual lines etc. around by vertex movement to get a better looking fit.


    vxon_kitt,


    It's not really rectifying with one point, that's not possible; but if your raster image of a map has the exact same scale and orientation as your real world map data, sometimes only one common point is needed to "position" it properly. Of course extreme projection differences are the caveat to this method, but you can try reprojecting your underlying real world data instead of reprojecting the image, and using that. Here is a general algorithm, many variations are possible:


    Open the raster image choosing the option NOT to manually rectify. This will give your image a Geographic Projection positioned in Quadrant 1 near 0/0 Lat/long.


    Use the measure tool to measure the scale bar, or some known distance on your image, do the math, and bring your image to true scale. You may have to "fine tune" your scaling a couple of times.


    Use the north arrow, or any known direction on your image, and (if necessary) rotate it so that azimuths on your image read correctly with the GM measure tool. Fine tune if necessary.


    Use the "shift layer" function to translate your image to very near it's desired position. Make the raster layer semi-transparent, and you can continue to visually "massage" it's position to get the best possible fit. Use the measure tool and an azimuth/distance shift for small moves.




    Mike is probably shuddering at this barbaric use of GM as a photoshop-like tool, but some "ball park" coordinates, or a "rough location" for a map feature in a picture is sometimes better than nothing. This is the kind of thing that either works, or it doesn't, for a particular map image; but it's often worth a try.


    Mark
  • global_mapper
    global_mapper Administrator
    edited June 2012
    Mark,

    I have added an item to the todo list for allowing drag-and-drop type tools for shifting and rotating images. It would be more useful for "fixed screen position" type layers like logos, but once it works for one should work for all. We are also planning some similar tools for free-form rotation of vector features in the v14 release.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • Nick Hardy
    Nick Hardy Global Mapper User
    edited June 2012
    Thanks Mark. I have done 4 other images and got into the swing - once you have your eye in it is much quicker than my first try.

    Mike - I will keep my eye open for the new version. I think the "drag, drop and rotate" using the mouse will be faster to get it into roughly the rifgt location.Then fine tune with the "scale, rotate, translate" window using the keyboard (so don't remove that option if you add the "drag and drop").

    Thanks again all.
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