Ice Age Mark · Global Mapper User


Ice Age Mark
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  • Specify file prj on import without being prompted


    The best way to do it is to use DEFINE_PROJ and END_DEFINE_PROJ to define your import projection 'before' your import.  You give it a name (or it already has one), and then specify it using that name in your import command.  Then it's in the script for any import to find just by calling it's name.  Like:


    Projection     GEOGRAPHIC
    Datum          WGS84
    Zunits         NO
    Units          DD
    Xshift         0.000000
    Yshift         0.000000
    0 0 0.000 /* longitude of center of projection


    The example above should be good for EPSG 4326

    Hope that helps,


  • Problems cropping raster with digitized area feature (GM 18.0.3 Win7 Enterprise SP1)


    I'm still on V17, but it seems I remember this when checking out the Beta V18.

    When I moved my crop polygon to it's own new layer (instead of User Created Features), it worked fine.  I think it might be a bug.

    Hope that works, if not you'll have to wait for BMG Bob.

  • How do I rectify 64 layers with WGS projection to a site grid of Northings and Eastings


    The local grid problem is always a 'challenge' (also known as a PITA).  Your goal (to have your map layers correctly scaled, oriented, positioned, and displaying coordinates in your local system) 'should' be possible, but it must be done in several stages.  Try this procedure:

    Step 1 - Get a real world starting point near the site to create the property line/corners.

    Use Google Earth, zoom in, and create a point on your site as near to a property corner as possible.  Export/Save the point from GE, and import that .kmz point into a new empty GM session (i.e. no projection or layers yet).  Importing the GE point should make the projection become Mercator (GE sphere datum)  Now change the projection to the CA SPCS Zone you are in.  Pick feet as Planer Units.  Make the datum be NAD83.  You want NAD83 here because it's almost identical to WGS84, which is the datum of the real world points you will use later to translate.

    Step 2 - Use COGO to create the boundary as a vector feature and then rectify your map image to it.

    Select the point, then the COGO function. Start with the corner nearest your GE point and use the bearings and distances of the boundary to create a vector line feature that is the property line. (Go counterclockwise so you don't have to reverse the bearings)  This boundary doesn't "close", but let that go, you just want the corner points.  Import your map image and choose to manually rectify.  Choose the CA SPCS Zone and datum you used above for a projection.  [With GM you can just zoom to a property corner on the map image, click a point, then zoom to that corner in the reference image and GM will snap to it.  Then click add point (no need to enter any numbers that way)].  Do this for all 5 corners.  Pick triangulation for a rectification method.

    At this point your map should be roughly scaled, oriented, and located fairly near it's real world location.  Check this now with GM online imagery.  If you're far away something went wrong and you must try again.  If you are close, you will find that now your equirectangular local grid has been distorted from rectifying to the (likely erroneous) boundary bearings/distances.  The squares are rhombs and their area is not 10,000 sq.ft. as it should be.   

    Step 3 - To solve this you must create a vector grid of 100' squares with GM, then re-rectify the map image to that grid.  This part can be tricky.

    Use the 'create user grid' to make a 100' x 100' grid and anchor it to the nw'ly most local grid intersection.  Now select your previously rectified map and chose to re-rectify.  DELETE the old control points that are the property corners.  Now re-rectify like above, but use the grid intersections for your control.  Use at least 5 intersections so you can use triangulation as your rectification method.

    Now your map 'should' be properly scaled and oriented (check it), but it will still be off some in it's real world location (check this also with online imagery).  Here is where your real world coordinates (Lat/Long in WGS84) get used.  I can't help much with this part because you cannot share the site location.  However, I think you don't want to rectify for this step, you only want to 'translate' (shift horizontally) using one point, and see how that plays out.  If you rectify, your local grid may become distorted again.  It depends on the nature/projection of your real world coordinates, which I don't know.

    Step 4 - Lastly, if this all works, you will find that your coordinates are in CA SPCS, and not in your local grid system.  To solve this you must create a custom projection.  This is fairly easy, but again I cannot help with out the real data which you can't share.  In essence, you would use the 'extra false northing/easting' parameter in the SPCS projection to offset the coordinate values by cranking the math.

    This is pretty involved, but it 'should' work.  I have likely overlooked something, so don't hesitate to ask for help.  I think if you try it, you will see the concept, and be able to intuitively make it work for your situation.

    Best of luck,