Torsten The image of the xvi file makes it look as though there is a loop (not sure if it is a plan or elevation view – presume it is elevation). Also if you have a fixed point at each end, then this could also cause ‘a loop’ which might give differing elevations at each end. Also, if the water is flowing, then the water levels at each end will actually differ. But I assume you have correctly assessed these effects as negligible, or at least not detected by your survey method. I think you are implying that the 0m line is a raster background. If that is the case, it may be distorted by Therion. One way to check would be to turn on gridlines for the layout. That will show you what Therion really thinks is a horizontal line. Also check that Therion has the water surface survey stations at the same altitude. You can check this easily by interrogating a .3d output with Aven. Bruce From: Therion <therion-bounces@speleo.sk> On Behalf Of Torsten Schnitter via Therion Sent: Tuesday, 30 October 2018 04:36 To: therion@speleo.sk Cc: Torsten Schnitter <torsten.schnitter@netcologne.de> Subject: [Therion] ***UNCHECKED*** Problem with elevation view Hi all I have a under water cave survey and all the data is done with depth measurements. So the Z coordinates are absolute and the survey is not with clino data. The cave starts at one point and after roughly 800m you have another surface point. When I compile the data I get a strange behaviour. Although it's not a WYSIWIG map editor I would expect points which have the same depth are at the same "depth"/level on the xvi file. But they are not (see attached screenshot "elevation problem"). The 2 points within the red marks do have the same depth measurements. But if you have a closer look to it you can see they are not at the same level. (They differ somehow in x/y way and therefore the points are not on top of each other.) There are no loop closures inbetween which could be a reason for different levels. Not having the same level with these points (I assume it is this point) leads to a bigger problem later on. When drawing the elevation scraps and putting a water surface (depth = 0m) to the scraps and having a raster in the background, the surface at the beginning of the cave is not at the same level than at the next surface point of the cave. But it should be. See pictures "elevation problem-start" and "elevation problem-end". What's wrong? Can anybody help? If more info is needed please let me know. Thanks, Torsten