<div dir="ltr"><div><div><div><div><div><div><div><div><div><div><div>Hello List,<br><br></div>I'm trying to convert some LiDAR data from NAD83(Original), with orthometric heights based on CGVD28, to WGS84 with ellipsoidal heights, and to NAD83(CSRS) with orthometric heights based on CGVD2013.<br>
<br></div>I've been verifying my output using NRCAN's online GPS-H tool (<a href="http://webapp.geod.nrcan.gc.ca/geod/tools-outils/gpsh.php">http://webapp.geod.nrcan.gc.ca/geod/tools-outils/gpsh.php</a>), and not getting good results.<br>
<br></div>To begin with, I use las2las to convert my data to WGS84, using parameters:<br><br></div>--a_srs '+proj=utm +zone=12N +ellps=GRS80 +geoidgrids=HT2_0.gtx'<br></div>--t_srs EPSG:4326<br><br></div>Then I go from WGS84 to NAD83(CSRS) with the following:<br>
<br></div>--a_srs EPSG:4326<br></div>--t_srs +proj=utm +zone=12N +geoidgrid=CGG2013n83.gtx +ellps=GRS80 +datum=NAD83<br><br></div>Now, I don't actually have a decent way of verifying my output, other than with GPS-H, and the disagreement seems significant. For example, the original elevation at 494618.88mE, 6306815.69mN is 469.95m, and I get an ellipsoidal height at -111.088356°W, 56.90501°N of 444.52m. GPS-H claims that the orthometric height at that position (for HT2_0, the closest approximation to CGVD28) should be 470.004m, a difference of 54cm. <br>
<br></div>I realize there are a lot of points where this process could be going wrong, or that it's not going wrong at all. I wonder if anyone can give me any insight or fill in any obvious holes in my reasoning. If I've left out any pertinent information, let me know.<br>
<br>Note that I could just use GPS-H to process the points, but I need to automate the conversion of a lot of data, and establish a reusable process to do so. And, I'd like to use this opportunity to learn about proj!<br>
<br>Thanks,<br></div><div>Rob<br></div><div><div><div><table style="border-collapse:collapse;width:195pt" border="0" cellpadding="0" cellspacing="0" width="195"><tbody><tr style="height:15pt" height="15"><td style="height:15pt;width:65pt" align="right" height="15" width="65">
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