http://opentopo.sdsc.edu/jforum-2.1.7-b3/posts/list/20.page JForum - http://www.jforum.net A good question from an OpenTopo user regarding misaligned tiles downloaded from the system - this isn't the first time this issue has been identified, so I'm posting the problem and solution here: "Could you please look at the two files listed below, they were downloaded from GeoEarthScope Northern Calif LiDAR Project. fg596_4149 fg595_4149 ...The two tiles will not line up side-by-side like they should (east to west). The east-most tile (ug596_4149) seems to be shifted up or north relative to the adjacent tile (ug595_4149)? I view the LiDAR imagery through ESRI GIS v9.3. I also use the imagery to view my Trimble GPS data.When I place the GPS data, the locations appear to be the right scale, but shifted in the wrong place on the tile" Here's an image to illustrate the issue:]]> http://opentopo.sdsc.edu/jforum-2.1.7-b3/posts/list/33.page#67 http://opentopo.sdsc.edu/jforum-2.1.7-b3/posts/list/33.page#67 GMT Explanation and solution: "This is a known issue with the early deliveries of the NoCal data and has been resolved for the later deliveries. When NCALM exported the tiles a few had the wrong projection assigned seemingly at random. If you look at the projection of the tile offset to the north (ug596_4149) you'll see that it is "Clarke_1866_UTM_Zone_10N" instead of the "WGS_1984_UTM_Zone_10N" projection assigned to the rest of the dataset (including tile ug595_4149). The fix here is to use the "Define Projection" tool in ArcToolbox to redefine the projection for tile ug596_4149 to what it should be (WGS_1984_UTM_Zone_10N)...note that you want to redefine the projection NOT reproject the data. The data in the tile have the correct coordinates, Arc just gets confused and puts it in the wrong place because the projection definition is wrong." -cc]]> http://opentopo.sdsc.edu/jforum-2.1.7-b3/posts/list/33.page#68 http://opentopo.sdsc.edu/jforum-2.1.7-b3/posts/list/33.page#68 GMT