Latest Contributions by MelitaKennedy

Hello, I read that the geoid is very close to the real earth shape(less than a meter off the MSL) and that it is at most 100m away from the WGS84 spheroid, then I saw such models where the MSL seems to be thousands of kilometers away from any spheroid, are those hugely exaggerated and inaccurate models or am I misunderstanding something? (from my understanding 100m shouldn't be noticeable and a good earth model should be a spheroid - almost a sphere - 22km difference between the spheroid axis shouldn't be noticeable as well). Thanks for the help. The geoid model: See original post for the graphic Hi, Yes, it's definitely been exaggerated. I seem to remember reading somewhere that the surface of the earth is smoother than the surface of a bowling ball (relatively). There are some numbers here: http://www.geography.hunter.cuny.edu/tbw/GTECH201/notes/5.Earth.Coordinates.Grid.Coordinate.Systems.Notes.pdf on page 5. Melita ... View more

I created a personal geodatabase in which I want to import GPS-derived features (with trimble gps Analyst extension). for the databese I chose geographic cordinate system  in WGS84 and set the xy domain to the default values min = -400 (for both x and y) and max = 400. However, when creating a new feature dataset within the *.mdb, setting the same projection (or importing it) the resulting domain has higher maximum values for x and y (= 9006799.25474099 instead of 400). I can't see why this is happening, or how I can change it as it is not possible to define the spatial domain itself when creating the dataset, nor change it within the properties. Since the spatial domain of the database is smaller than the one of the dataset, I get an error when importing GPS derived features for postprocessing purposes. Thanks for any advice Katharina Katharina, The large values are correct. In a high precision feature class/dataset, the maximum allowed value is around 9000 trillion as an integer value. The XY/Z/M domains and resolution values convert between the real world double precision values and internally managed positive integers. That's with a resolution size of 1. When we set the XY (Z/M) domain minimum and maximum values to something reasonable, that means the resolution value is very, very small which increases storage requirements and processing time. Instead, only the minimum XY/Z/M domain values are used plus a more reasonable resolution values. The maximum values are set based on the minimum values and the resolution, and thus the maximum values become very large. You may want to take a look at this white paper: Understanding Coordinate Management in the Geodatabase Melita ... View more

Hello! Is there a way to combine Coordinate Frame transformation method and custom grid-based NTV2 method into single transformation method? Right now, in ArcGIS Desktop there is only possibility to choose either first or second method, but have anybody tried to combine these two into singular one? Thanks in advance! Many greets, Vojkan Gajovic, GISDATA Belgrade Serbia Hi Vojkan, We plan to add this functionality at 10.1 to ArcMap--at least to combine two existing transformations. If they're new, you could then define them with the GP tool, Create Custom Geographic Transformation, and then use them in ArcMap. For now, the only in ArcMap is to create a tool/script. I'll post a VBA sample, but I haven't made a similar add-in for ArcGIS 10 yet. Melita Sub twoGT()     '1)Create our factory   Dim pSpatRefFact As ISpatialReferenceFactory2   Set pSpatRefFact = New SpatialReferenceEnvironment   Dim pGeoTrans_A As IGeoTransformation   Dim pGeoTrans_B As IGeoTransformation     '2)Use the factory to create our geotransformation objects   Set pGeoTrans_A = _     pSpatRefFact.CreateGeoTransformation(esriSRGeoTransformation_ED1950_To_WGS1984_1)   Set pGeoTrans_B = _     pSpatRefFact.CreateGeoTransformation(esriSRGeoTransformation_Belge_1972_To_WGS_1984_1)     '3)Create a composite geotransformation object   Dim pGeoTransComposite As ICompositeGeoTransformation   Set pGeoTransComposite = New CompositeGeoTransformation     '4)Add the two separate geotransformations to the composite   pGeoTransComposite.Add esriTransformForward, pGeoTrans_A   pGeoTransComposite.Add esriTransformReverse, pGeoTrans_B   '5)Give the new transformation a name.   Dim pNewGeoTrans as IGeoTransformation   Set pNewGeoTrans = pGeoTransComposite   pNewGeoTrans.Name = "ED_1950_To_BD_1972"     End Sub ... View more

A friend of mine sent me some raster files. The raster files are good in every way, except for the extent. The extent of the raster file is completely off. I know what the new extents need to be, but I have no idea how to change them. If you know how to change a raster's extent, please post it. Hi, There are two issues that may be occurring. 1) the rasters are not georeferenced. The extents reflect the number of cells in the raster like 0.5,0.5 to 999.5,999.5. If this is the case, see Fundamentals for georeferencing a raster dataset 2) The raster has no coordinate system information, so ArcMap isn't able to project it on-the-fly (in memory) to match your other data. In this case, you need to define the coordinate system. Once that's done, you can use the Project Raster tool to create a copy in a different coordinate system. Defining or modifying a rasters coordinate system Melita ... View more

I'm having trouble getting data from my GPS unit in WGS 84 to show up correctly when I change the projection to MTM 3 Degree.  Do I need to change the projection more than once before it's correct?  I'm also not sure of the transformation I need to use (if that's the problem), I'm displaying data in Toronto I think what you should do is leave the data defined as WGS84. Then use the Project tool to create a new dataset in MTM, or let ArcMap project it on the fly (in memory). Melita ... View more

Hi, I have XY value tabel having with NAD 27 Zone 6, I want convert this vales to NAD 83 Zone 6. Thanks, GM You'll want to look at IGeometry2:ProjectEx. By Zone 6, do you mean a state plane zone? Possibly in California or Alaska? Here are some snippets. The first creates a projected coordinate system based on NAD27. Private Sub CreateProjectedReferenceSystem()     ' Set up the SpatialReferenceEnvironment.     ' SpatialReferenceEnvironment is a singleton object and needs to use the Activator class.         Dim t As Type = Type.GetTypeFromProgID("esriGeometry.SpatialReferenceEnvironment")     Dim obj As System.Object = Activator.CreateInstance(t)     Dim srFact As ESRI.ArcGIS.Geometry.ISpatialReferenceFactory = obj         ' Use the enumeration to create an instance of the predefined object.         Dim projectedCS As IProjectedCoordinateSystem = srFact.CreateProjectedCoordinateSystem(esriSRProjCSType.esriSRProjCS_NAD1927SPCS_CAVI) ' California 6 End Sub The enumeration for NAD83 California 6 is esriSRProjCS_NAD1983SPCS_CAVI. You'll also want to look at Understanding geotransformations which has a link to code on how to create an existing transformation. If the data is in California, you'll want to use esriSRGeoTransformation_NAD_1927_TO_NAD_1983_NADCON. Melita ... View more

Dan, Set the forum to "show threads active within": 1 year. Here's a link: http://forums.esri.com/forums.asp?c=34&dy=365 Ooh, and you can change &dy=### to a larger number to return more threads. Nice. I didn't know that. Although this may be something to look at for the old forums--add more options to the "show threads active within" pull-down list. Melita ... View more

Hi, for an application I have to get the unit of the coordinate system of a featureClass. (I'm using VBA) What I do is: I take the layer with the FeatureClass. Then give the Layer to IGeoDataset. The Reference System of the dataset I pass to IGeographicCoordinateSystem or IProjectedCoordinateSystem. Finaly i get the unit from IUnit. My problem is: Bevor I pass to IGeographicCoordinateSystem or IProjectedCoordinateSystem, I have to know, if it is a GCS or a PCS. Otherwise I get an error. I didn't find out how I can check this before. Does anyone of you have an idea? You should be able to use something like this:     If TypeOf pSpatialReference Is IGeographicCoordinateSystem Then         MsgBox "GeographicCoordinateSystem"     End If         If TypeOf pSpatialReference Is IUnknownCoordinateSystem Then         MsgBox "UnknownCoordinateSystem"     End If         If TypeOf pSpatialReference Is IProjectedCoordinateSystem Then         MsgBox "ProjectedCoordinateSystem"     End If Melita ... View more

Does anyone now if the Geodatabase Reporter is available for ArcGIS 10.0? If not, will it be available in the near future? Any alternatives? The Geodatabase Reporter for 9.2 says to use ArcGIS Diagrammer if using 9.3. The ArcGIS 10 version of ArcGIS Diagrammer is here: http://resources.arcgis.com/gallery/file/arcobjects-net-api/details?entryID=F12ADF8F-1422-2418-34B2-C276C6BCCF98 Melita ... View more

When using the new XY To Line tool the Line Type is provided. However I cannot find anything regarding more detailed descriptions of the Line Type. What is the difference between GEODESIC and NORMAL_SECTION? Also, what are some examples as to when are the best instances to use which tool? Type of two-point lines to construct. Default line type is GEODESIC. GEODESIC�??Straight line based on a spheroid. GREAT_CIRCLE�??Straight line on a sphere. RHUMB_LINE�??Line of constant bearing (direction). NORMAL_SECTION�??Straight line on a spheroid. Hi Daniel, A normal section is a simplified version of a geodesic line. It's easier to construct, but won't quite be the shortest path. It is defined by the intersection of a plane that passes through two points on the surface of the spheroid and is perpendicular to the surface ('normal') at the first point.  Melita ... View more

Thanks, Melita.  Just a couple more questions: 1) Is it possible to store the geographic transformation on the layer, rather than on the map, so that each layer could use a different transformation?  I looked through the documentation and I didn't see anything, so I suspect the answer is 'no', but I thought I would ask anyway. 2) Can I create an IGeoTransformation using an EPSG code instead of the ESRI code, or map an EPSG code to its associated ESRI code?  I tried to create a NAD83 to WGS84 NADCON transformation using the EPSG code, but I got an error saying that the code was not valid for a geographic transformation.  The documentation describes a method for creating a spatial reference from an EPSG code, but not a geographic transformation. Thanks. Bob Hi Bob, 1) No. We have had several people ask for that functionality, but haven't scheduled it for a software release yet. 2) ISpatialReferenceFactory:CreateGeoTransformation which takes an integer 'code'. Where we can, we use the EPSG codes for our well-known IDs/codes. If you use an EPSG code and the object isn't created (using the appropriate function), we don't support it yet. We also have macros, or enumerations, under esriSR<objtype>. There's some code on GeoTransformationOperationSet here: http://help.arcgis.com/en/sdk/10.0/arcobjects_net/conceptualhelp/index.html#/How_to_use_the_IGeoTransformationOperationSet_methods/000100000m6z000000/ Hope this helps! Melita ... View more

Hi, I have a file geodatabase that I created in v10 but I need to provide it to someone who is running 9.3.1. Is there a way to convert my database from v10 to v9.3.1? You can't convert it directly, but you can create a 9.3 geodatabase using the Create File GDB tool in the Workspace toolset of the Data Management toolbox. http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//0017000000pw000000.htm "Jay" on http://gis.stackexchange.com mentioned that James Fee has posted a set of empty geodatabases from the various ArcGIS versions on his blog. You can find them here: http://www.spatiallyadjusted.com/2006/11/21/esri-92-personal-geodatabases-in-arcgis-91/ Melita ... View more

Thanks, Melita.  That info looks promising. A couple of questions: 1) In your example, you say that only NAD_1927_To_NAD_1983_NADCON is loaded by default, then the code adds NAD_1927_TO_NAD_1983_AK to the collection.  Does this replace the original NAD_1927_To_NAD_1983 transformation, or add a second one?  If it adds a second one, how does ArcMap determine which one to use when converting from NAD27 to NAD83?  Does it prompt the user? 2) Will changes to the geographic transformation list is be saved with the map document? Cheers, Bob Hi Bob, I'm sorry that I wasn't clearer. 1) Only one transformation per pair of GCS is allowed, so the Alaska transformation will replace the "NADCON" (actually for contiguous US, the lower 48). 2) Yes, the GeographicTransformationOperationSet is saved in the map document. Melita ... View more

Thanks, Venkat. Is there an event that fires before ArcMap starts the automatic transformation? Is this automatic transformation done using a geoprocessor?  If so, how do I get access to the geoprocessor so I can handle its ToolExecuting event?  I'm looking for something that will allow me to hook into ArcMap in order to possibly update the IGeoTransformation before the input features get transformed to the data frame's coordinate system. Thanks, Bob I don't know if there's an event, but part of what you're looking for is IMapGeographicTransformations. See VBA (sorry!) below on how to change the default transformation loaded upon opening a new map document. Only NAD_1927_To_NAD_1983_NADCON is loaded by default. Private Function MXDocument_NewDocument() as Boolean    ' Start by getting a handle on the current FocusMap    Dim pMxDoc As IMxDocument    Set pMxDoc = Application.Document    Dim pMap As IMap    Set pMap = pMxDoc.FocusMap    Dim pSpRFc As SpatialReferenceEnvironment    Set pSpRFc = New SpatialReferenceEnvironment    Dim pAlaskaNADCON As IGeoTransformation    set pAlaskaNADCON = pSpRFc.CreateGeoTRansformation(esriSRGeoTransformation_NAD_1927_TO_NAD_1983_AK)    '  Add the transformation to the operation set    Dim pGTSet As IGeoTransformationOperationSet    Set pGTSet = New GeoTransformationOperationSet '  The Map uses IMapGeographicTransformations to access the geogtrans    Dim pMapGeo As IMapGeographicTransformations    Set pMapGeo = pMap    Set pGTSet = pMapGeo.GeographicTransformations    pGTSet.Set esriTransformForward, pAlaskaNADCON    pGTSet.Set esriTransformReverse, pAlaskaNADCON End Function Melita ... View more

Sorry about the attachment I must have made it too small. The original XY plots were in meters and I used the calculate geometry tool to change this to DD. This worked just fine, but with some negative values. These values were commonly negative to -2 or -3 DD, these points fall outside of the UTM grid I was told to put the points into (37N) so are an eventuality I figure. Thank you very much for your help. Oh, I see. I bet the negative DD values were in the latitude/Y field. Thanks! ... View more