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Hmmm, I've done this type of thing many times and if both transformation definitions are set up properly, it works fine. You can see small differences if the rotation parameters are large (over 9" or so) because changing the signs is an approximation. But 140 m sounds like the transformation isn't occurring at all. Some difference in the GCS definitions between what's defined in the transformation and the data or data frame GCS? Melita
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09-21-2011
09:03 AM
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A transformation is always an approximation, so unless a target layer was created by using the same transformation, you will likely see differences. There will also be differences if positions were re-surveyed--a transformation is unlikely to match the new values. So it's not really that the source/target ellipsoids are different, that's just a part of the whole thing.
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09-21-2011
09:01 AM
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At minimum, the data frame's coordinate system would have to be unknown, because ArcMap will 'wrap' or clip data to the equivalent of 360 degrees, or the valid area of use of a projected coordinate system.
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09-21-2011
08:55 AM
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If you're using the Create Custom Geographic Transformation tool or the New Transformation dialog in ArcMap, you only need to define it in one direction. In fact, it's very slightly more accurate to define the transformation as-given, because then the software can invert the transformation's rotation matrix (more necessary when the rotation values are relatively large). If, for some reason, you do need the parameters for the opposite direction, simply change the signs so: dx(m) = -89.5 dy(m) = -93.8 dz(m) = -123.1 rot(x) = 0 rot(y) = 0 Rot(z) = +0.156 Scale = +1.200 Melita
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09-20-2011
07:32 AM
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There should be no effect. Both projections are well-defined, and I consider them 'lossless'. Yes, there could be some very small movements in the coords, but well below data accuracy (like 5-6th or more decimal place). It's possible you might lose data between them. Mercator is chopped off near the poles, so if you had data there, it would get clipped out. Yes, web Mercator uses a sphere, but it's all being handled internally, and when data is unprojected back to lat/lon you get the original lat/lon values. Melita
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09-13-2011
09:37 AM
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This is just a guess, but are all the data using the same coordinate system? And more importantly, is the GPS data using a foot-based projected coordinate system? Melita
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09-12-2011
03:14 PM
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Hi, You're getting the right coordinates. Northern hemisphere UTM zones have a Y/northing origin at the equator so any data below there will have negative Y values. Southern hemisphere UTM zones have a Y origin at the equator too, but add a false northing of 10000000 m. That means all Y coordinates in the southern hemisphere will be positive. Points above the equator will have Y values larger than 10 million meters. Melita
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09-08-2011
11:11 AM
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Just taking a stab here--IRasterInfo::Extent? (I don't work with rasters at the ArcObjects level)
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09-06-2011
05:10 PM
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Oops, I had the resampling methods backwards! Thanks for correcting me, and I'm glad that you solved your problem. Melita
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09-06-2011
07:16 AM
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I'm sorry, I should have posted about this earlier. Make sure the tool (or geoprocessing settings) is using nearest neighbor. And, more importantly, the cell size is 30m. The difference between WGS84 and NAD83 in the contiguous US (48 states) is about a meter. I wouldn't bother reprojecting the raster. Use its property page in ArcCatalog or the Define Projection tool to set it to NAD83. Melita
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09-05-2011
06:29 PM
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Hi Nate, I'm sorry that I wasn't clearer in the earlier message. Use the Define Projection tool or the data's property page in ArcCatalog to change the coordinate system NAD83 UTM Zone 18N. Or you could just clear the coordinate system--make it unknown first. Add it and the other layer to ArcMap. Set the data frame to use NAD83 UTM 18N. If the State Plane data lines up with the point layer (with an unknown coordinate system), you've confirmed that the point layer is using UTM 18N. If a layer has no coordinate system, ArcMap can't do anything to it except display it. ArcMap can't project it to a new coordinate system. It can project layers with a known coordinate system. So you try setting the data frame's coordinate system to what you think the unknown data is in. Melita
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09-01-2011
02:02 PM
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Hi Nate, Just going by the coordinates, I would guess a UTM zone, either 17North or 18North. Because the easting values get pretty small, I think it's 18N. Melita
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09-01-2011
11:40 AM
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There have been other posts about Calibri like: http://forums.arcgis.com/threads/17743-Calibri-Font-issues-in-PDF-after-ArcMap-Export There are a few possible solutions, but nothing that works everywhere. Melita
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08-31-2011
12:45 PM
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