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Just discovered an interesting situation when coming to amend some MXDs and generate area calculations. A previous consultant - when creating the first MXD and project data, set the correct spatial reference in the data frame but must have built all data creation (digitisation) off an image that was not correctly referenced.

All the data has now been created at around -104.09°, 40,118°. This was discovered when georeferencing an engineering drawing for the site and then calculating areas from features digitised and realising the scale didn't match up.

Is there an easy way to convert all data coordinates to the correct location? Re-referencing data based on a correctly referenced set of imagery would be too time-consuming for the project needs, and it's not a situation where assigning a new spatial reference is appropriate, as it has the correct spatial reference on the dataframe and the feature classes - it's just that the coordinates are out entirely.

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    Use spatial adjustment toolbox – FelixIP Aug 11 '16 at 5:38
  • Create a backup!!! Define the projection to what the data was created in using Define Projection resources.arcgis.com/en/help/main/10.2/index.html#//… and then Project resources.arcgis.com/en/help/main/10.2/index.html#//… to what you want it to be.. assuming there is a transformation you should be done. That is also assuming the data was accurate and only incorrectly defined previously; you do know what coordinate system the data is in don't you? If the georeference was done incorrectly first and the data is not accurate then @FelixIP is right. – Michael Stimson Aug 11 '16 at 5:39
  • @MichaelMiles-Stimson Seems like the best route. The image is a nearmap image that has no spatial reference associated with it. I have tried defining it as GDA94 which I believe should be correct, however now I can't find it all. Zoom to layer does nothing. Any ideas what's going on there? – malcoholic Aug 11 '16 at 5:46
  • If it has no spatial reference associated with it then defining as WGS84 will not be correct... the default UL is 0,0 and cell size of 1,1 will put it in the southern hemisphere heading toward Africa - not what you want. The Spatial Adjustment toolbar will allow you to put in displacement vectors (essentially georeference) for the digitized features - you can save and reuse them when you get a good set. An Affine transformation should be all that's required if your original image and correct location is in projected coordinates but going from geographic to projected will need higher order – Michael Stimson Aug 11 '16 at 5:52
  • @MichaelMiles-Stimson True. While it had no reference, the image does have lat/lon values in the filename which I assume is the centroid point. Would that allow for any shortcuts that you could see? – malcoholic Aug 11 '16 at 6:05
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First, create a backup!!

Open up ArcMap, ensure the Spatial Adjustment toolbar is turned on and add some data that you trust to be in the correct location and with some identifiable similarities (Orthophotograpy is good, roads or parcel information can also be helpful)

Using the Spatial Adjustment Toolbar add some displacement links from-to (from where the data is to where it should really be) - add quite a few and concentrate on the edges of your data but don't forget the middle. The amount of displacement links depend on your adjustment method, how good your data is and your expectation of the results; a simple affine can be done with only 4 widely spread links and can become confused with too many (more than 20) but a rubber sheet works best with a lot of links fairly evenly distributed (but don't make them too close)..

Choose an adjustment method; Affine should be all that's required for a straight scale 'n rotate, if the data is essentially correct and in the same spatial reference but in the wrong location. Data digitized in a different or unknown spatial reference may need a higher order transformation or rubber sheet if the data is really bad or originally inaccurate.

Open up the links table and have a look at the links with really bad RMS (root mean square) - perhaps you've snapped to the wrong end of a feature. Because you've added heaps of links you can delete the really bad ones and still have enough. Preview the transformation as you go to assure yourself the result will be suitable.

If you have to do this for a few datasets you can save the links ready to reload for the next feature class. Note you can operate on all features loaded into ArcMap but may want to do this on a few computers at once - you can share the file around to help.

Now that you're happy with the parameters and links (you should also have a backup of the original and links just in case) you can perform the transformation - this used to take an extrordinarially long time but now it's not too bad.

If you notice after transforming that there's an area (or two) that could have been better you can go back to your backup, load your links and add a few more to pin down the last little bits...

  • Thanks Michael. Also worth noting that those saved links can also be used as links for georeferencing for any rasters that need to be adjusted as well - was helpful in my case as there was also several overlay images of plans that had been georeferenced to the same set of problematic unreferenced aerial imagery, and I could just re-use the saved links from the Spatial Adjustment. – malcoholic Aug 15 '16 at 5:16

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