Georeferencing a raster overlay using one point, true north, and a bar scale

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02-28-2014 09:19 AM
LukeMazza
New Contributor
I have a bunch of maps I'd like to overlay in ArcMap but almost all of them don't have more than one point I can georeference. These are cave maps and they often have one entrance which I have coordinates for, an indication of true north, and a bar scale. I assume that's enough to get me in the ballpark but I'm not really sure where to start. Any tips would be appreciated.
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3 Replies
NidhinKarthikeyan
Regular Contributor II
You should have a minimum of 4 Control Point to Georeference a raster. Else you should have an existing spatial data (target data), such as Georeferenced raster or a Vector Feature Class of the same location. Take a look at this weblink: http://resources.arcgis.com/en/help/main/10.2/index.html#//009t000000mn000000
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NeilAyres
MVP Frequent Contributor
You can, carefully, mark 3 other points on your map scaled off from your single origin.
Then re-scan and use these for the GCP's to do the image GeoRef.
Very do-able.
Cheers,
Neil
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LukeMazza
New Contributor
That's a great idea Neil. Thanks!
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