Surface Anomaly w/contours

[mpeterson79]

This drawing contains three surfaces:
A surface imported from Google Earth
A surface created from a DEM
A surface (FG) created by first pasting the Google Earth surface, then the DEM


The DEM is a 10m surface. I smoothed the FG surface using NNI, with a 12m grid. This is the result:

http://www.gallery.markspeterson.com/d/9856-1/Surface+Contours+02.jpg


Anyone care to explain what's going on, or what I'm doing wrong that I'm ending up with the strange contour 'web' over the river?

[MHultgren]

Hi MPeterson,
Did you create Breaklines or a hidden Boundary along each side of your River edge?

Maybe the wind was blowing when they did the DEM and Google Surfaces? :lol: Just kidding!

I would probably create Proximity breaklines along each river bank or use a Hidden boundary to trim out the contours inside the river.

[ekubaskie]

The points in the DEM may wobble from just above to just below your contour value. I see it with LIDAR data too, only worse.

The accuracy of the Google Earth surfaces aren't all that great, either. I've seen a number of them that show differences of as much as 50' in the elevation going across large water surfaces.

Then you try mixing data from the two sources, the inaccuracies could cancel themselves out, or compound.

[sinc]

You can also get radically different elevations for the same site, depending on the zoom factor.

[ramon_tavarez]

The surface model from Google Earth are not good. Don´t use it if you have more accurate data.

If you need to "complete" some data, try to adjust the elevations of the model form GE to make them reach the elevations of your DEM.