Latest Contributions by MelitaKennedy

Hi Jaimie,  We would not be able to provide you with any transformations, so yes, there would be no transformations. We only have one "known" definition for WGS84. Even if you created custom geographic coordinate systems that included the realization and epoch date the software has no way to handle it correctly. I don't know if the difference between your two epochs and realizations are insignificant or not. It will depend on your accuracy needs. If the data's in the US, you could try the HTDP software from the National Geodetic Survey and calculate what the differences are. Melita ... View more

Hi Henry,  So far we are not differentiating between the WGS84 realizations. That will change in an upcoming release, as EPSG plans to add them.  I sometimes link a ITRFxx version with WGS84 in the transformation name, as a hint to which realization the transformatoin applies to.  At 10.4, we added support for GEOCON v1.1 which converts between the "last" HARN re-adjustment and NSRS2007 or NSRS2007 to 2011. GEOCON is file-based, so I don't think Collector supports them. The files are also in a separate install, 'ArcGIS Coordinate System Data' or 'ArcGIS Pro Coordinate System Data' as the data files were getting too large to include with the core software. We don't have equivalent equation-based transformations because NGS hasn't released any. These are probably the best we have: "WGS_1984_(ITRF00)_To_NAD_1983_2011" "WGS_1984_(ITRF08)_To_NAD_1983_2011" You could take HARN as approximately equivalent to CORS96 and chain together the 1st transformation above, with  "WGS_1984_(ITRF00)_To_NAD_1983_HARN" Or just use them to get the HARN data up-to-date. Another possibility is to run the GEOCON transformations (there's a beta v2.0 as well) using the NGS converters to see what the offsets look like in your area of interest.  Melita ... View more

I can, but I'm internal. It's on hold as we were not able to find a mathematical solution easily and Esri-China was going to do some work on their end for it. I haven't heard anything for at least a year. Melita ... View more

Hi Jason,  No worries. This area of GIS has been getting more, rather than less, complicated over the years!  A realization is sometimes called a re-adjustment. All the control points in the network are run through a least-squares adjustment (which shakes everything up a little) and then the control point coordinates are updated based up where they are at the time. It takes into account subsidence, tectonic motion, seismic events, etc. Sometimes there are transformations (which are just best fit) between realizations, sometimes not, or the transformations are released years after the realization is put into practice. Pretty much every 'new' geographic coordinate system (datum) that was based on ITRF/WGS84 uses the same ellipsoid, GRS80, but how that surface fits the earth will vary a bit.  ITRFxx and WGS84 (Gxxxx) have more mathematical definitions and are tectonic plate-agnostic. They vary very little over time. NAD83 and its realizations/re-adjustments are bound to the plates (North American, Pacific for Hawaii and American Samoa, and Mariana for the Guam and the Marianas) to try to minimize the change in coordinates over time. That works well for a lot of places, but the west coast, Louisiana, Alaska, Hawaii all have issues. That also means that the NAD83 realizations are moving away from the ITRFxx/WGS84 (Gxxxx) frames. NAD83 <> / != WGS84 any more! The county systems like MN and OR got particular realizations versions depending on when they were added. The WisCRS system was added when the HARN re-adjustments will still going on in some parts of the US, but Wisconsin had had their done for a while. We added a NAD83 (2011) set at 10.4.1. The Oregon sets were added in discussion and cooperation of the Oregon DOT. Basically, it's very difficult to add and maintain several versions of the projected coordinate systems based on different realizations so both we (ESRI) and the EPSG (an online registry of coordinate reference systems and transformations) try to limit them.  Melita ... View more

The F subscript represents the "false origin" aka the latitude of origin parameter. No subscript means you should use the current point's latitude, but that would only be needed on the forward case (from lat/lon to xy), not on the inverse case. You might want to try repro-ing the example in the guidance note, as that will clearly show if the calculations are correct or not. ... View more

Yes, you should be able to use the 7-2 Guidance note, or Snyder's Map Projections: A Working Manual.  Parts that might not be so apparent (more if using Snyder than the guidance note) is that you subtract off the false easting and northing values first, then convert the new values to meters. This is because the ellipsoid's semimajor axis (in your case, GRS80) is usually defined in meters. Angular parameter values also need converted to radians.  Lambert conformal conic isn't one of the really hard projections to implement, but it's not one of the easy ones either!  Do you not have the Spatial tools? It looks like it's already implemented there... Melita ... View more

I'm just speculating based on what I little I know about ArcGIS. Part of the save-as-previous-version code is checking various libraries on what was or wasn't supported at that particular version. Because that information is likely in multiple dlls, it might not be easy have a stand-alone utility that doesn't need the entire software. (Esri employee, but I work at the bottom of the software stack, mostly) ... View more

Please post the extents, the current coordinate system, and approximately where the data should be (city, county, state, lat/lon). Once you look at the extents, you should see that they're different. One will make sense for the coordinate system and the other won't. For instance, if the coordinate system is a geographic one, the extent has to be between lat: -90 to +90 and lon: -180 to +180. If you've got coordinates larger than that, they're using a projected coordinate system.  Melita ... View more

Try running the Check Geometry Tool and if anything is found, Repair Geometry Tool (on a copy of the data). Also, try deleting and recreating the spatial index.  ... View more

Hi Jim, Yes, particularly with imagery which has its own resolution, that would likely work (convert to HARN).  Identify some coordinates at the edges of your area of interest, plus some interior points. Try to include points at the low and high points as well. I'm pretty low-tech. Stick them in a text file like: ID,lat_nad83,lon_nad83 Add the file to ArcMap with the Add XY Data option. Make sure to set the coordinate system to NAD 1983. Right-click the layer to export out a shapefile which we'll call nad83input.shp. Use that in the Project Tool, set the output coordinate system (CS) to NAD 1983 HARN. Use the NAD_1983_To_HARN_North_Carolina transformation. Set the output shapefile's name to nad83harn.shp, and so on. If you add them all to ArcMap but do not set any transformations, you'll be able to see the offsets. You could also add the coordinates into the attribute table and then copy them to Excel to automatically calculate the differences. Or keep adding fields to each new shapefile and calculate the current coordinate values. Then you can see how the data's trending between the different re-adjustments.  Particularly with the HARN to NSRS2007 and the NSRS2007 to 2011 transformations, NGS wouldn't create transformation grid files because the standard deviations were about the same size as the offsets themselves. They did find that it wasn't just noise so a few years ago, they did create grid files. There are newer ones in GEOCON v2, but we haven't implemented them yet. You might also contact your state Geodetic Advisor, Gary W. Thompson, or the mid-Atlantic advisor, Scott Lokken. Details at the link addresses. Melita ... View more

Maybe the symbol isn't defined correctly? But that's a wild guess on my part. ... View more

Hi Jim, Thank you for the kind words.  This gets interesting. Technically, the "NAD 1983" geographic coordinate system should be the original, 1986 version. However, a LOT of people have used it for every other possible re-adjustment. Unless there's metadata/history, it can be very difficult to determine which data is really HARN (and there might be multiple versions in some states), NSRS2007, etc. The conversions between NAD83 (86) and HARN will be the largest, with the HARN/NSRS2007/2011 conversions much smaller, cm-level usually.  You might want to run some test points in various areas through each transformation, NAD_1983_To_HARN_NC, NAD_1983_HARN_To_NSRS2007_GEOCON_CONUS, and NAD_1983_NSRS2007_To_2011_GEOCON11_CONUS.  Depending on the data accuracy, the transformations, particularly the last two, may not really matter. As I mentioned earlier, the GEOCON transformations were added at 10.4.1, and need the separate ArcGIS Coordinate System Data setup.  Melita ... View more

I interpreted the question as asking for help to find a topic for a senior or capstone project. I think he asked a similar question on GIS stackexchange but it was quickly closed as off-topic. I can't find it now. ... View more