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

emedleyemedley Global Mapper UserPosts: 17
I have spent hours trying t solve a simple problem: how do I rectify a series of layers (64 raster and vector) to a project site which has a Northing and Easting co-ordinate layout?  I created a trial workspace, imported a raster image of the site with the grid and rectified the image (without a Reference image) with 8-9 GCPs using the coordinates. The base projection is WGS. Would Orthographic be better? The units are feet/miles.

Cursor location info shows the coordinates OK, but obviously I have not input the correct scale because when I try to measure areas i get millions of square miles... 

I also tried creating a layer with several points with attributes of Northings and Eastings, but am missing how to inform GM to convert the layer from WGS lats/longs to my site coordinate system.

Once I do this rectification for one layer how on earth do I do it for all 64 layers? Select all of them at one time and do .. what?..

I am using GM 20.1 64 bit, b040419


Answers

  • tikhpetrtikhpetr Posts: 39
    Hi!
    Could you more specifically describe the target coordinate system?
  • emedleyemedley Global Mapper User Posts: 17
    Simple north-south oriented grid of Northings and Eastings. A coordinate for one point may read 2503 E/8904 N. units are feet. Site is about 1000 feet by 600 feet, and is oriented NW/SE. See attached image. The "CCxx" points are selected points that have attributes of the Eastings and Northings, but I could not use that array to re-project the image to the site grid. Silly me, no doubt.. 

    I imported all my layers as raster images of air photos and maps. I rectified all my layers relative to a few key ones and they are geo-referenced in the existing projection of WGS84, the default GM projection.. But the underlying scale is of course miles, and the coordinates are degrees/minutes all arbitrary as per default when importing rasters into GM. I really should have sorted this problem out when I began but at that time I did not care about site dimensions, areas etc,; only getting reasonably good overlays. 

    My overall goal is to re-project my entire database of 64 layers to the Site grid. I am having memory issues too. I should have created a Map Catalog but don't know how to do that now without disrupting the links to my GM workspace... 




  • tikhpetrtikhpetr Posts: 39
    Sorry, my English is bad. Please lay out one raster sheet.
  • sphillipssphillips Posts: 184
    Do you know what the coordinate system is for your site? If so setup your workspace using that coordinate system and use the Latitude and Longitude values provided to georeference the image using Geographic Lat/Long (default). Once done see what the Easting and Northing values are from your cursor location and see if they match to the grid values. If they partially match (last 4 digits only) it may mean they are based on a local/site grid. I often see this where the data is shifted closer to the origin (truncated) by certain x and y distance.
  • emedleyemedley Global Mapper User Posts: 17
    I checked if the coordinate system is CA State Plane, with last 4 digits used/ But it is not. If I knew the coordinate system I would not have a problem - I would rectify to that. 

    This seems such a trivial problem given the power of GM. 
  • sphillipssphillips Posts: 184
    I often have to find out what coordinate systems are used for data sent to me - and a lot of the time the data is in a local/mine grid. If it helps this is my basic workflow for finding out which one out of over 2500 basic coordinate systems it is! If you don't have any success make sure to double-check the grid units are feet and not meters. I am sure you have already done so but just mentioning it before you go though the list below.

    1. Using Google Earth create a point on your site and note or copy the Lat/Long coordinates. Use Decimal Degrees (In Google Earth go to Tools > Options > 3D View > Show Lat/Long > Decimal Degrees). 
    2. Export the reference point to KML for use later.
    3. Enter the Lat/Long coordinates for the project on this site to find the most common coordinate systems for that location: https://georepository.com/search/map. Once done go to the Projection tab and look at the list. Highlight one of the names you feel is plausible and right-click and do a Google search to find the EPSG code to use in Global Mapper.
    4. Import the Google Earth KML into Global Mapper. This will be your reference point for the next steps.
    5. Note the approx. Eastings and Northings (x and y values) for your site
    6. Using the EPSG code change the coordinate system to one on the list and see if the cursor coordinates for your point are a close match (the most important digits are the last 4)
    7. Without unloading the point, changing the coordinate system and repeat the previous step.

    With regards to georectifying. If the maps are exactly the same pixel dimensions and are of the same view you should be able to save the points used during georectifying and reuse them. 
  • emedleyemedley Global Mapper User Posts: 17
    Your procedure did not help, Im, sorry to say. I can see what I am to do but my GM balks at searching for projections by ESPG codes. (I do not have a license for GeoCalc, although I can do co-ordinate transforms using the Co-ordiante Converter Tool.). I suspected that my co-ordinates were California State Plane (ESPG Code 15309) but they are not, neither are they UTM. Yes: I am looking at the last 4 digits. 

    I do have geographic coordinates for points on my site as well as the Northings and Eastings for the same points.(See the graphic I uploaded a couple of days ago).   If I rectify for these points the cursor position shows the northings and eastings correctly in the info bar at bottom of the GM screen. BUT, the scale is still in miles. I cannot see how I can instruct GM to simply transform using the few points I have with geographic and northing/eastings input as feet. 

    Thanks for your help. 
  • tikhpetrtikhpetr Posts: 39
    Try searching for your coordinate system here.
    http://epsg.io/
  • sphillipssphillips Posts: 184
    Can you upload a map? The image was unreadable due to the quality.
  • emedleyemedley Global Mapper User Posts: 17
    sphillips:  The image is the map. I cannot provide a crystal clear image because the project is confidential and I do not want the Site recognized. The image shows a grid of coordinates: it should not matter what what the site details look like, surely? I uploaded the image at at the request of tikhpetr. 

    tikhpetr: I did investigate http://epsg.io/. The site does not help me. I know that my site can be related to WGS84, UTM and California State Plane survey projections. But the UTM and State Plan coordinates are not the same as mine (I am looking at the last 4 digits). I get that I need to find a projection "close" to mine, but GM will not let me search on the ESPG codes that I input (eg: I input ESPG code 15309 for CA State Plane and I get an error message that tells me "Unable to determine projection or datum for ESPG Code". 

    It seems like a real easy transformation. Rectify my layers to the arbitrary coordinates shown on the image that I uploaded. Pick two or three GCPs from the image (say at cross-points), input the coordinates from the image and then (somehow) tell GM that those coordinates are scaled in feet. Currently the current coords are WSG84 (false with meridian of 0 degrees nearby- my geographic coord are close to 0 degrees). But obviously the scale is way off: miles instead of feet. The site is only 700 feet by 400 feet in dimensions. 

    I have even tried to reiproject to CA State Plane but then my workspace view goes to white space. I also have "Coordinate out of range" showing my status bar..

    If I try rectifying with  a few GCPs with "correct" Easting and Northings those coords show in my status bar but the underlying projection is still WSG84 with false lats/longs and the scale is not correct/

    I am repeating myself. Sorry.


    I ge
  • sphillipssphillips Posts: 184
    Without knowing the Lat Long for the site I will not be able to help find the correct coordinate system sorry. I understand why you can't share this info though.

    Note that SPCS83 Alaska zone 9 (EPSG:15039) is meters not feet.


  • tikhpetrtikhpetr Posts: 39
    emedley  wrote that he had California.
  • MykleMykle Global Mapper User Posts: 450Trusted User
    "ESPG code 15309 for CA State Plane" is what he wrote.
    That is also meters, not feet.
  • tikhpetrtikhpetr Posts: 39
    I made a mistake! :D EPSG 15309
  • tikhpetrtikhpetr Posts: 39

    4.png 25.5K
  • Ice Age MarkIce Age Mark Global Mapper User Posts: 319Trusted User
    Hello,

    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,

    Mark
    sphillips
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