Latest Contributions by MelitaKennedy

To convert between ED50 and WGS84 with data post-2001 use ED_1950_To_WGS_1984_23 aka EPSG:1612. How wide an area does it cover? You could use a UTM zone if the area of interest fits within that extent. Otherwise, possibly a conic projection, but you would have to use a custom one. Melita ... View more

Hi Hollie, Unprojecting data is converting it from a projected coordinate system to a geographic coordinate system, so using the Project Raster tool. If the Project Raster tool is losing precision, the default calculations it uses to pick an output cell size may be getting confused. Try setting some of the tool's or geoprocessing environment parameters. Melita ... View more

Hi David, That would be true only if the algorithm is taking the coordinate system into account. Let's take a (almost) worst case scenario: WGS 1984 Web Mercator Auxiliary Sphere. It's not conformal nor equal area (and definitely not equidistant except along the equator), but the same issues will apply to other projected coordinate systems. The scale at a point is 1/cos(latitude), so a point at 40N has a scale distortion of 1.3 and an areal distortion of 1.7. Now let's talk about a point on the central meridian of a UTM zone. Point scale is 0.9996 and areal distortion of 0.9992. If the algorithm is not taking the coordinate system into account and is using 2D Cartesian calculations, you're going to get different answers. We've been upgrading or modifying some algorithms to take the coordinate system into account like the Measure Tool and the Buffer Tool, but many algorithms used by different tools are still 2D Cartesian. Melita ... View more

Not a guru, by any means! But I see a partial solution. If any points are beyond the ends of the runway, you would have to make an extended line version first. Use Near to calculate the perpendicular distance to the runway and the location of that point, then you'll have to figure out how to calculate the along-runway distance. Melita ... View more

Hi Leifster, No, we don't support the TOWGS84 parameter nor do we support including a transformation WKT in the prj file/spatial reference information. We're 'late-binding', not 'early-binding'. You only pick a transformation when you need it. Using the Create Custom Geographic Transformation tool, the definition is persisted for you so you can then use the same transformation in the Project tools, for instance. Another possibility is the projection engine environment variable, PEOBJEDITHOME, where you can define a coordinate system or transformation, including giving it a WKID. The definitions would have to be set up before starting ArcGIS, and if you do need to define a custom spheroid, it gets a little complicated (you have to define the geogcs, datum, and spheroid separately). If you're interested, send me an email, mkennedy at esri dot com. Melita ... View more

The first layer that has this extent: Layer extent Top: 363757570.5 Left: 696914.08 Right: 708387.16 Bottom: 3628739.22 is not in WGS84. It sounds like you defined its coordinate system (spatial reference) to be WGS84 using the Define Projection tool or the data's property page in ArcCatalog. That updates the metadata, not the actual coordinate values. Did the layer have a coordinate system before? If you know it, or can find it, define it back to that system. Then the two layers should overlay. Melita ... View more

Inês, Shapefile 2 is not in UTM, but in latitude-longitude. Try redefining its coordinate system to WGS84 using the Define Projection Tool or the data's property page in ArcCatalog. Then, if necessary, you can project it to UTM. Melita ... View more

Ah, it's on ArcScripts with the same ID: Convert Points to Lines I haven't used it. Melita ... View more

Hi Everybody:     I am making a data manipulation tool to handle some WGS84 data.     There is some data with "fake" WGS84 spatial reference, which means: when I use ArcCatalog to look at the property of the datasets and feature classes, it shows WGS84. However, the underlying data is actually NAD83. The tool I developed will not give correct result with this kind of data. How can I identify these kind of data? I want to put some data validation logic to the tool to reject this data. Any idea>     Thank you! How do you know that the underlying data is NAD83? Is the data really in a projected coordinate system based on NAD83? If that's the case, you could check the data extents. Data in a projected coordinate system will have much large extent values than data in a geographic coordinate system. Melita ... View more

We use Vincenty. ... View more

Hi Andrea, Do you mean in layout view, adding a graticule to the map? That functionality was never added to allow it to label 0-360. You might have to create the grid, but unlabelled and label it by hand or use the Create Fishnet tool to generate a graticule, but again it would have to be labelled manually. Melita ... View more

Hello, We haven't added any VCS that reference GEOID12A yet. Vertical transformations aren't supported yet, but you can define the VCS on your data. It's a bit odd on how we have set up the VCS definitions because we use a late-binding method for our transformations. There's a WGS 1984 geoid VCS that isn't connected directly to a particular geoid model like EGM96 or EGM2008. Melita ... View more

If you add the attached shapefile to ArcMap first, it will set the data frame to 0-360 in WGS84. If you want to use a different GCS, use the Define Projection Tool to change the coordinate system. Melita ... View more

Hi Martes, The top/bottom values are negative. That has nothing to do with how many zones (width) the data covers. You only get negative Y (northing) values if the data is in the southern hemisphere, and is using a northern UTM zone. Change the coordinate system (Define Projection or ArcCatalog data property page) to zone 37N. Or maybe not. By the way, the east-west extents aren't that wide, but if the data covers eastern Democratic Republic of the Congo through Tanzania, I think it's in UTM 34N, not 37N. Melita ... View more

I'm having difficulty calculating the latitude and longitude values of an image that I am hosting inside of a div tag on my webpage. I can easily figure out the x,y (pixel) coordinates of the image and save them to a variable inside of my script. Here's the tricky part... The map is not a mercator projection, so I cannot simply linearly interpolate the x,y pixel coordinates to lat and lon values. However, I do have the luxury of knowing the latitude and longitude of all four corners of the image (see posted diagram), projection of the map on the image, central meridian, and latitude of origin. [ATTACH=CONFIG]22484[/ATTACH] The 800x600 pixel image is of the U.S. and I am basically trying to capture the latitude and longitude on click by passing the x,y pixel coordinates. I am assuming I will need some sort of transformation function. Similarly to what was suggested on gis.SE, you can georeference the image. I *think* you're trying to do this outside ArcGIS software, although you can do some of these steps in ArcGIS. So, because you know the most of the projected coordinate system of the image, recalculate the corners into Stereographic (on a sphere--what sphere?), using the given parameters. At that point, you can then interpolate an individual location into the stereographic coordinates, then either implement the map projection's inverse yourself, or use proj.4 or whatever to unproject to lat/lon. The only times you could reliably interpolate directly to lat/lon with an image that's in a projected coordinate system is if the image is very large scale and doesn't cover a large area or the map projection has square latitude/longitude 'squares'. Mercator doesn't (they elongate north-south as you move away from the equator), thus one of William Huber's comments on gis.SE. In your case, you've got a small scale map covering a large area using a map projection that definitely doesn't have square lat/lon sections. Melita ... View more