Latest Contributions by MelitaKennedy

Also, Esri does not support the TOWGS84 keyword, so you cannot rely on it to include a datum transformation. Melita ... View more

You can make something quite simple through Notepad, for instance. In the file, ID,latitude,longitude 1,20.0,75.0 2,20.25,75.0 3,20.25,75.25 4,20.0,75.25 The latitude and longitude values must be in decimal degrees, not degrees-minutes or degrees-minutes-seconds. Melita ... View more

Hi Sean, Without the projection parameter values, it's going to be difficult to figure out what might be in use. Is it US data? You could try the local state plane zone (based on NAD27 which uses Clarke 1866). You'll still need to identify points on the map for which you have coordinate values. You may have to georeference it directly to lat/lon. Melita ... View more

If you want to georeference to a Lambert-based India zone, you'll have to get coordinates in that coordinate system that you can use for the georeferencing. One way is to 1. create a text file with the lat/lon coordinates, 2. add it to ArcMap with Add XY data, setting its GCS to use Kalianpur 1937 (which uses Everest) 3. set the data frame to use the India zone, 4. right-click the layer in the table of contents to access data, export data tool. 5. set the tool to use the data frame's coordinate system and save the data as a shapefile or feature class. Melita ... View more

Hi Dean, Try setting the NAD_1927_To_WGS_1984_2 transformation in ArcMap. Open data frame properties, select the coordinate system tab, click the Transformations button on the right side. Because you add the WGS84 data first, the "to" (pulldown) should list WGS84. In the top box, select NAD27 if it isn't. In the bottom pull-down select NAD_1927_To_WGS_1984_2. OK all dialogs. ArcMap has to be told which transformation to use, just like the gp tools. The two step process you listed will give you different results. The first NAD83-to-WGS84-1 doesn't really do anything. It assumes NAD83 and WGS84 are equivalent. The second will only transform data in the lower 48 states (down to around 23N) so again no shift. The north-south offset is likely just due to convert the lat/lon values to UTM but with different spheroids (Clarke 1866 vs WGS84). Melita ... View more

Hi Dean, I can't tell from your post. Did you set the transformation in ArcMap as well? Melita ... View more

Hi Katalin, This comes up pretty frequently on the forums. The issue is that the target (or sometimes the source) coordinate system is based upon a sphere. We don't have any transformations to/from a sphere because they're not a true, geodetic geographic coordinate system/datum. In this case, it is easier to use ArcMap. Ignore the transformation warning, and export the data. Basically, the input/output GCS differences are ignored and internally, the data is redefined as the output GCS if no transformation is available. That's what was happening in ArcInfo Workstation. The on-the-fly projections in ArcMap are not less accurate than using the Project tool, unless no transformation is set when it's needed. In this case, it's not needed. If you instead want to set up a custom transformation, use Longitude_Rotation for the method which doesn't have any parameters. This is emulate the 'don't do a transformation.' Hope this helps, Melita ... View more

Hi Dean, Did you project the data on-the-fly in ArcMap and then export? Did you set a geographic/datum transformation? The Project Tool will require a transformation if it's needed, but there are often multiple transformations between two geographic coordinate systems. NAD27/WGS84 has over 20 possibilities, mostly based on area of interest. What's the data extent? If you used Project Tool, again, the coordinate in the attribute table (.dbf) are not updated automatically. The actual coordinate values are stored elsewhere if you're using a shapefile. You can update the fields in the associated dbf file as I mentioned before. Melita ... View more

Hello, The viewable information in a DBF file is attribute information only. Coordinate values, etc are not updated automatically. If you have 10, you can use the Add XY coordinates tool (Data Management, Features), or in ArcMap, use calculate geometry for the fields. Regards, Melita ... View more

Easting and Northing implies that the coordinates are in a projected coordinate system. You'll need to figure out what that is, in order to overlay this data with other datasets. If the data's in the US, it could be in UTM or State Plane (using which GCS/datum and unit?) or even a statewide definition. Melita ... View more

We supported that pcs in 9.3.1, but with WKID = 102186 (not in EPSG yet). At 10, we changed the WKID to 3775 to match EPSG. Melita ... View more

Hi Anne, First, try setting a transformation to convert between Adindan and WGS84. There are several possibilities. If the data's in Ethiopia, try Adindan_To_WGS_1984_4. You're correct that the transformation will likely move most of the points into the area of interest, but not all of them. Perhaps check the original values again to confirm that the conversion to decimal degrees worked correctly? Were the original values in degrees-minutes or degrees-minutes-seconds? Melita ... View more

Hi James, Yes, what you're seeing is correct. When you change the coordinate system in ArcCatalog via the data's property page, or with the Define Projection Tool in ArcToolbox, only the metadata is updated. The coordinate values themselves are unchanged. So you have NAD83-labeled that is still georeferenced to NAD27. Use the Project Tool instead to create data that is on NAD83. Melita ... View more

It's a difference between ArcGIS versions. 102185 is an Esri-assigned WKID. 3401 is the WKID assigned by the EPSG Geodetic Parameter Dataset. Because this is more widely acknowledged, we change andy Esri-assigned WKIDs to EPSG's once a definition is added to the Dataset. Melita Note: I'm a member of the subcommittee that maintains the EPSG Dataset. ... View more

Hi Markus, Hmmm, there was NIM039228 which matches your problem but it was fixed in 9.3.1. It reappeared in 10.0, and was fixed in sp1 (NIM060606). I haven't been able to find any other open bugs for it. Melita ... View more