Latest Contributions by MelitaKennedy

‎03-07-2013

Hi Noel, ArcGIS can do the conversion, but isn't set up to do individual coordinates. You could convert your points into an XY Event layer, transform or reproject them, and/or convert the layer into a permanent feature class. This workflow has the benefit of allowing you to overlay the points against reference data. If you just want to convert a few values by hand, you can check values in ArcMap on the status bar (in the data frame's coordinate system). Or for a stand-alone program, perhaps CORPSCON would be useful. Melita

‎03-06-2013

Hi Mike, If you were using the Measure Tool in ArcMap, it may be defaulting to the projected / Cartesian distance. That is, the distance in the projected coordinate system. Usually if you switch the tool to use the geodesic distance, you'll get a closer-to-ground measurement because the geodesic distance is based on the shortest path on the spheroid (ellipsoid) that's being used. Because, at best, only some distances are maintained in any map projection, measuring the projected coordinate system distance can give some very distorted results. In your particular case, Mercator is definitely not designed to minimize distance distortion, particular at higher latitudes. Meridians (longitude lines) don't converge to the poles in Mercator so distance measurements will get worse and worse as you go North or South away from the Equator. Caveat: Esri's implementation of Mercator does include a standard parallel parameter. Set that to the area of interest and distance measurements will improve, but still won't be very accurate. UTM uses transverse Mercator which does have the meridians converge at the poles, and is designed for larger scale data. That's why the results are better than Mercator. Melita

‎02-25-2013

Hi Nick, Thank you for the data link. That makes things a lot easier! ArcGIS can read the .prj file that contains the coordinate system information, and will correctly interpret the data as using decimal degrees in a geographic coordinate system. It should line up (overlay) correctly with your other data in WGS84 as-is. However, the "WGS 84" names for the GEOGCS and DATUM don't match the Esri definition of "GCS_WGS_1984" and "D_WGS_1984" (although we will ignore the GCS_ and D_ when comparing names). Thus, you may be a warning message about different geographic coordinate systems/datums and that a transformation may be needed. You can ignore the warning too. If you plan to reproject the data into a different GCS or do certain types of processing, it may be easier to update the data's coordinate system definition to the ArcGIS one. Using the Define Projection tool, select the data. For the coordinate system, browse to geographic coordinate systems, world and select WGS 1984. OK everything and you'll be good to go. Melita

‎02-22-2013

If the input data is lat/lon referenced to WGS84, you could just use the Define Projection tool to change the definition to match what ArcGIS expects. Because the output fc is empty, I'm wondering if the input coordinate system is defined incorrectly, so when the Project tool tries to reproject it, the coordinate values are corrupted. If you think that this is the problem, could you post the data's extent plus a general idea of what location it represents (in lat/lon or nearest city, county/state, etc.). Melita

‎02-21-2013

Ah, yes, the DNAG coordinate system. See link for two different ways of assigning the coordinate system. If you're going to use the well-known text version by using it in a .prj file at 10.1, you can use the "import" option and browse to the file to select it. There aren't any geographic/datum transformations. One way to deal with it is to unproject the data to STM1987 and then try redefining (not reprojecting) it as NAD 1983. Melita

‎02-15-2013

You might try IBufferConstruction / IBufferConstructionProperties instead. It supports geodesic-based buffers on points at 10.0.

‎02-13-2013

Hi Diederik, I think you should choose one of the existing Antarctica-based projected coordinate systems. As an example, I'll use UPS South. The definition is located in projected coordinate system, polar. In ArcMap, open data frame properties (right click in the map and select properties from the context menu OR right click Layers in the table of contents and select properties). Select the Coordinate System tab. If using 10.1, 1. Type in UPS in the search box, then open the resulting folders to find UPS South. Select it. 2. Right click UPS South and click "copy and modify". If using 10.0, 1. Browse the folders to the Polar group and select UPS South. 2. Click the Modify button. Next steps are the same for either version. 3. Change the central meridian value to -15 or whatever longitude value you want to have pointing up. You may also want to change the projected coordinate system name so that it's clear that it's a custom definition. OK all dialogs. All data layers that have correctly defined coordinate systems will get projected on-the-fly (in memory) to this coordinate system. If you want to convert data permanently to this coordinate system, use the Project Tool, or right click a layer in the map and choose data, export data. In that dialog, use the data frame's coordinate system. Melita

‎02-12-2013

Hi, Am Ali and I live in Sierra Leone. I would like to know how to calculate the Scale factor in my region (UTM Zone 28 with central meridian of 15 degrees), given a control point of latitude 8.680658 degrees, longitude -12.51276 degrees and elevation of 168.754 above mean sea level. ArcGIS Desktop doesn't have a tool to calculate the point scale factor for a map projection like transverse Mercator. The US National Geodetic Survey has a tool that will convert the convergence and scale factor for NAD83 (which uses GRS80). The scale factor will be practically the same for WGS84. Northing Easting Zone Convergence Scale Factor 960443.960 773700.612 28 0 22 32.26 1.00052717 If you want the point scale factor for the Sierra Leone 1960 datum (based on Clarke 1880), you'll have to find a different tool. The scale factor due to a map projection doesn't have anything to do with the elevation at the point. That makes me wonder if you're looking for something like a "combined scale factor" that includes elevation. Here's an excel spreadsheet that does it, but it would also need adjusted if you want the information based on Clarke 1880 rather than GRS80/WGS84. Melita

‎02-04-2013

Hi Nathan, The problem with converting or defining the other layers as NAD83 is we don't know what they're in now. If we can't figure it out, you may have use the spatial adjustment toolbar to force them into a known coordinate system. Did she have any base data underlaying these layers? If so, that may be the coordinate system. They're using. It almost looks like the x/easting values are in NAD83 Georgia East (USfeet), but the y/northing values were converted to feet twice. Hmmm. Melita

‎02-04-2013

One of the original sources is John Snyder's Map Projections: A Working Manual. It also contains the state plane parameter values (NAD83 changes from NAD27 are listed in an appendix). If you use Jeff Pace's code as a template, please note that the "map units" of the first section are in US survey feet, not meters. Melita

‎02-04-2013

The TAZ layer (in Georgia statewide Lambert) appears to be around Macon, Bibb County, more or less. The other layers might be in state plane (Georgia East), but the Y values don't match up. I also checked UTM, but that didn't match either. Melita

‎01-31-2013

If it's in a 'known' coordinate system like a UTM zone, you can define its coordinate system with the Define Projection tool or its property page in ArcCatalog. If you don't know its coordinate system or it's a 'local' coordinate system, you'll have to georeference it. You may want to start here in the help: About georeferencing CAD datasets Melita

‎01-30-2013

Hi Vanda, Your best resource is your instructor. One possibility is that older versions of the Spatial Analyst supported GRIDs only, although I think you could pass in different imagery types, the output was always in GRID format. But that's no longer true as of version 10.0. Even at 9.3, it would automatically convert various input raster formats. Maybe the homework hasn't been completely updated? Melita

‎01-25-2013

ESRI.ArcGIS.Client.Projection Namespace > WebMercator Class : FromGeographic Method ? There's a similar method under the Bing namespace, but it works with MapPoints.

‎01-23-2013

Hi Megan, Earlier you said that the data ended up in the wrong hemisphere so here are two things to check. Are the longitude and latitude fields labeled correctly? If you're using x and y for the field names, x = longitude and y = latitude. Also, if the data is in the US, the longitude values must be negative. Melita

My Ideas

Latest Contributions by MelitaKennedy

Re: northing and easting

Re: Coordinate Systems

Re: Failed conversion from WGS_1984 to GCS_WGS_1984

Re: Failed conversion from WGS_1984 to GCS_WGS_1984

Re: Issue with USGS Decade of North American Geology projection

Re: How to convert the meters to degrees in GCS_WGS_1984?

Re: How to rotate a map ? (ArcMap 10.1)

Re: How to Calculate Scale Factor using UTM WGS84 Coordinate System

Re: Layer's don't match / Wrong Projection?

Re: Math for converting coordinates

Re: Layer's don't match / Wrong Projection?

Re: Adding CAD data with no spatial reference into arc map.

Re: Convert an image to a GRID

Re: Convert Graphic (polygon) coordinates

Re: Using Excel sheet to geocode xy (lat/lon)

Re: New XY layer from Lat Long (DD) not plotting c...

Re: EPSG release and ArcGIS Projection Engine

Re: EPSG release and ArcGIS Projection Engine

Re: The vertical transformations WGS_1984_To_EGM96

Re: The vertical transformations WGS_1984_To_EGM96

Coordinate Reference Systems

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