Confusing contour elevation question

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peter-hughes-davies

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?ÿI received a drawing file containing contours generated from a point cloud and while the elevations seem to be at their appropriate elevation, in that a front or side view shows them stacked at their correct interval, the properties list shows them at for example 235', -236', 237', 238', -239' in an apparently random array of positive and negative values.?ÿ Then, if you try to change the negative elevation to positive elevation in the properties window a contour originally at say -236' will actually move to -236' when you apply a +236' correction to the elevation property.?ÿ The original and current coordinate system is a local assumed xy & z.?ÿ Very strange . . any theories on how this happens and how to correct it??ÿ

All input welcome and thanks in advance . .

Peter

Posted : February 15, 2018 2:54 pm

paden-cash

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This happened to me at least once.?ÿ Craziest thing I ever ran into.?ÿ I was working (in MicroStation) with a 3d AutoCAD drawing from the City of their countour GIS layer on their ortho info.?ÿ But the original drawing was an AutoCAD file.

I think I wound up destroying the line strings complexity (explode for all you AutoCAD folks) and then moving them one by one to their proper elevation.?ÿ It was a tedious pain in the keester.?ÿ But it was exactly as you described; the element info would read a positive elevation and its physical location in the drawing was at a negative value.

Posted : February 15, 2018 3:19 pm

peter-hughes-davies

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"Fire in the hole!"?ÿ . .?ÿ ??ÿ . .?ÿ Exploding and then globally rejoining the resulting line segments seemed to knock some sense into them and resolved the faulty z property.?ÿ Didn't even need to move them individually to their correct z location.?ÿ

Thanks very much for your much appreciated help?ÿ ? . . I have to wonder though what caused it.

Peter

?ÿ

Posted : February 15, 2018 3:49 pm

dick emery

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I've seen a couple of beauties from surveyors that weren't detected until time of construction. The first being the original ground topo for a 1000 lot subdivision, with two adjacent contours (1m interval) in the guts of it having the same elevation so that it appeared like a perfect internal dead flat ring road, and we didn't know whether one side was 1m high or low, or which side was wrong. The other being a completely missing bend in a sugarcane railroad topo survey, alongside which we were installing a buried 12" water supply pipeline - the bend went around a village, and the topo not only missed the bend, but had been seamlessly stitched at the ends so that half a mile of railroad/pipeline (and the village) was missing.

Posted : February 15, 2018 5:06 pm