I finally found the time to do some experimenting, using a single horizontal + vertical alignment. The report from RailTrack is this: (vertical curve, one singled out for easy comparison) Element: Circular PVC 95.206 7.321 PVI 119.377 7.333 PVCC 95.590 -792.679 PVT 143.504 5.885 VHIGH 95.590 7.321 Radius: 800.000 Length: 48.298 Entrance Grade: 0.048% Exit Grade: -6.000% I use the LandXML translator from RailTrack to create an XML file, here the same VA looks like this: 0.000000000 7.275193565 119.376711571 7.332524712 364.752123443 -7.390000000 587.349970853 -7.390000000 I imported the XML-file twice into MX, once 'as-is'and once without the negative vertical radii, as mr. Bradshaw suggested. None gave any errors during import, and the resulting alignments in MX are the same. mxmodel IMPORT01 ********Element 2 Vertical Curve******** IP Chainage 0+119.377 Curve Start Gradient .048 Curve End Gradient -6.000 High/Low Level 7.321 High/Low Chainage 0+095.611 IP Level 7.333 Curve Length 48.298 Vertical Radius -798.575 Curve Type Hog Curve Start Chainage 0+095.228 Curve Start Level 7.321 Curve End Chainage 0+143.526 Curve End Level 5.884 mxmodel IMPORT02 = without neg. radii ********Element 2 Vertical Curve******** IP Chainage 0+119.377 High/Low Level 7.321 High/Low Chainage 0+095.611 Curve Start Gradient .048 Curve End Gradient -6.000 IP Level 7.333 Curve Length 48.298 Vertical Radius -798.575 Curve Type Hog Curve Start Chainage 0+095.228 Curve Start Level 7.321 Curve End Chainage 0+143.526 Curve End Level 5.884 No noticable differences, but in both there is a slight change in the vertical radius, the source of concern for our client. In other alignments the change can be up to 5 meters To double-check I also imported both LandXML's to AutoCAD Civil3D 2014: IMPORT01: error during import Cannot solve vertical curve in at station 364.752123. Imported as a straight segment. IMPORT02 (the file without neg.radii) gave no errors, and the curve radii are unchanged at 800.000m and 3000.000m. So using only positive radii does make a difference in the way a LandXML file is read. But I still do not understand why MX messes with the radius........
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