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Edward Hakanson

Using the Earth Tools Utility of Rockworks

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Here in Costa Rica we are on a coordinate system called CRTM05 which uses the datum WGS84 (previously we were on the Costa Rica Lambert System with a datum in Ocotepeque, Clark 1964). For the CRTM05 system can define the easting and northing parameters easily enough in Rockworks but the geographical data is not displayed correctly in Google Earth. We are in zone 16N in the UTM system but I think that does´t have too much to do with the CRTM05 system because the numbers are not the same. An example of real coordinates in one of our field areas is 352000 E, 11820000 N. Other than the Easting and Northing correction is there anything else that I need to take into consideration so that I can get the images created in Rockworks to display correctly in Google Earth?



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I'm not sure about why your coordinates are not showing up in the right place but I have a theory. The first thing I noticed is that your northing is really large (you probably just have an extra zero). I also notice that if you take a zero off of your easting value, you actually get your point on land if you use zone 17 instead of zone 16. When I use an online utility to plot the points, like this one, https://www.rockware.com/freesoftware/ or this one, http://www.rcn.montana.edu/resources/converter.aspx both of the utm coordinates you supplied are in the ocean (when I take off the extra zero on the northing). Zone 16 is in the Pacific, Zone 17 is in the Atlantic with your adjusted coordinates. Is this where Google Earth is plotting the points? It sounds to me that you need to check the coordinate values for your points and that were properly converted or are in the correct zone.

From the research I've done, it looks like the problem arises in the Costa Rica TM 2005 datum. According to this: http://georepository.com/projection_5366/Costa-Rica-TM-2005.html the 'natural origin' is -84 degrees longitude with a false easting of 500,000. This is very similar to WGS84 UTM, but the difference seems to be the origin. A UTM zone is 6 degrees wide and this is true for the Costa Rica TM 2005 datum. The WGS84 standard zone goes from -90 to -84 with the center at -87 (the 'natural origin') http://spatialreference.org/ref/epsg/wgs-84-utm-zone-16n/ whereas the Costa Rica zone centers on -84 and goes from -87 to -81 which covers the whole country. This 'natural origin' was adjusted likely so that the zone 16 and zone 17 of the WGS84 grid would not result in zone errors. I would say that your Easting needs to be offset to get you in the correct position by what it appears to be 3 degrees of longitude.

I hope that helps.

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