Latest Contributions by MelitaKennedy

The EPSG 1612 reference on the datum is for a geographic/datum transformation, ED 50 to WGS 1984 (23). The software this data comes from must be "early-binding." That is, each GCS/datum has a transformation linked to it. ArcGIS is "late-binding." Data is tagged with a neutral coordinate system definition. When you need to transform it to another coordinate systems, then you pick a particular transformation. So define the data with ED 1950 UTM zone 32N (north). If you need to convert it to WGS84, use ED_1950_To_WGS_1985_23. Melita ... View more

Unfortunately, no, we don't support that projection. I think the closest would be the Cube or Fuller projections. Cube doesn't try to minimize distortions, but the Fuller projection does. Melita ... View more

We don't have any transformations for Everest 1830 because it's a ellipsoid (spheroid) and not a true geodetic datum/coordinate system. The data may be using Kalianpur 1937. Take a look at the geographic_transformations.pdf file located in your ArcGIS installation's Documentation folder for GCS that are used in India (or wherever the data is) and try some of them. It will mean redefining the Everest 1830 data with the Define Projection tool or the data's property page in ArcCatalog. Melita ... View more

Because they're showing up near 0,0 I think you're letting the Add XY Data tool set the coordinate system to the data frame's, which looks like Robinson or something similar (I didn't take a close look at the images you posted). When adding the xy data, change the coordinate system WGS84 or whatever geographic coordinate system, the values were collected in. ArcMap will then project on-the-fly (in memory) the points to the data frame's coordinate system. Melita ... View more

I saw a USGS website that stated that the GloVis imagery was all orthorectified. http://www.usgs.gov/newsroom/article.asp?ID=1425 Are you sure that these images aren't? Can you find other images for the same area that are already orthorectified? Melita ... View more

My guess is that different transformations are being used. That could cause small offsets like that. Particularly in Trimble Pathfinder Office, I don't know how to check what is being used. Melita ... View more

Hi Dana, Just a double check, but you used the Project tool and not the Define Projection tool? So you have two copies of the data--one in a geographic coordinate system and one in a projected coordinate system. The very small values sound like the data is still in lat/lon. Melita ... View more

That's great. BTW, when will 10.1 be released? Can we get a pre-release version? No idea! I know for beta clients, prerelease became available this week (the end of last week). I don't know if it's publicly available yet. Check with your local rep or distributor. The final version of 10.1...I believe we're saying Q2, so hopefully sometime before July. I really can't narrow it down any more. Melita ... View more

That's very good news. Thank you. In the case when there is no direct datum shift (transformation) available for the input/output coordinate systems specified, will the upcoming 10.1 provide a funtion to construct something going through an intermediate (e.g. WGS84)? The method is designed to include two-step transformations, both in the cases where there is no direct transformation and when overall accuracy would be better. Melita ... View more

... So our questions are: 1. Given the input and output coordinate systems, is there a way to construct a transformation that would convert data points from the input coordinate system to the output coordinate system, without knowing the datum shift or transformation by name? Both the input and output can be either geographic or projected coordinate system. 2. Assuming the answer to question 1 is yes. For a given pair of input and output coordinate systems, there might exist multiple sets of transformations, some may be direct, some may go through an intermediate like WGS84. Can we easily filter the transformation by some criteria, like the method (e.g. 7-parameter PVR, Molodensky), error, etc?  3. Are there some sample codes available? Our application is Java based, so ideally we would like something in Java. Thanks. We've recently added information into the Esri projection engine to help with this. Given the input/output coordinate systems and an extent, the function will return a sorted list based on data's overlap with the transformation areas of use and accuracies. The areas of use and accuracies aren't available in ArcGIS 10.0. ArcMap and the Project Tool will make use of it in the upcoming version (10.1). The ArcObjects 10.1 geometry library has exposed it through: SpatialReferenceEnvironment:: STDMETHOD(GetSortedGeoTransformations)(IGeographicCoordinateSystem* pFromGCS, IGeographicCoordinateSystem* pToGCS, IEnvelope* pExtent, IArray** ppGTs); ppGTs is a pointer to an array pointer in which the address of the array will be stored.  It will be an array of ITransformationPtr entries. Otherwise, I think you would either have to query the EPSG registry or store the transformation metadata information and process it yourself to find the best available transformation. Melita ... View more

Here's a blog entry about it: Setting the z factor parameter correctly Melita ... View more

I'm not quite sure what the problem is. Do the two datasets not overlay? As long as both have the correct coordinate systems, you should be able to overlay them within a hundred meters or so. If they do not overlay in ArcMap, what is the offset? Adding a ED50/WGS84 transformation should take care of most of any offset between ED50 and WGS84. Melita ... View more

It's possible, but it would have to be a custom transformation. We don't have any that use a GRS 1980 datum. You might try defining the 13 30 raster with the Esri version (use Define Projection tool) and see if that clears up the 5m offset. Melita ... View more

This GCS definition doesn't match the ArcGIS version of NAD27, so there are no valid transformations to convert it to NAD83 or WGS84, etc. GEOGCS["GCS_Geographic Coordinate System",DATUM["D_NORTH_AMERICAN_1927",SPHEROID["Clarke_1866",6378206.4,294.9786982]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]] Esri's version looks like this: GEOGCS["GCS_North_American_1927",DATUM["D_North_American_1927",SPHEROID["Clarke_1866",6378206.4,294.9786982]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433],AUTHORITY["EPSG",4267]] The capitalization of the DATUM name nor the Degree value matter, but the GCS name must match as well. You could use the Define Projection tool or the data's property page in ArcCatalog to set the coordinate system to the ArcGIS version. Melita ... View more

Perhaps the Resample Tool in Data Management, Raster toolset, Raster processing toolset is what you're looking for. Melita ... View more