Issue with the cross-section HEC RAS – ArcGis

[Anonymous]

Good afternoon.

So there is an issue. I’m making a geometric data by ArcGIS and HEC GeoRAS, the tin-file with landscape is made from srtm raster by ArcGis 3d analyst tools.

When I look on the cross sections in the ArcGIS, they looks normal.
But after converting the data to the HEC RAS, cross sections become too sharp, not as smooth as in ArcGIS, which lead to errors during the preparation to the flow analysis.

Please, help to find the reason.

P.S. the example files from the HEC RAS website with already made landscape tin-files do not have such a problem.

Best regards,
Aleksandr.

[Anonymous]

The screenshot with the issue .

[Scott Miller]

Try increasing the “Maximum Number of Points” when converting from raster to TIN in 3D Analyst. That ought to smooth the channel out. I usually bump it up by a factor of 10. It also helps to clip (data management) the raster to the area where the cross sections will be cut. Check the “Use Input Features…” box. Each of these approaches puts a greater density of vertices where they are needed.

[Anonymous]

First time I draw a contours from the raster and then create TIN from these contours. Now I made TIN directly from raster, and, as you said, strongly increased maximum number of points.
So the results:
1) the received TIN is not as correct and good as it was from the contours
2) the issue is repeated – ArcGIS shows that the cross-sections are smooth, so as they should be
But after clicking the “Export RAS Data” and opening the Geometric data in the HEC-RAS those cross-sections are very primitive and sharp.
May be the problem appears during that process of convertation?

[Anonymous]

https://gyazo.com/e102f375d469301b595cf5572c4233b7
Left is picture of cross-section from the ArcGIS, using the GeoRas instruments.
Right – same cross-section from the HEC RAS.
https://gyazo.com/636df9eb624a548d3bfb435cc5c0f03b
May be I`m doing something wrong when drawing the streamline, flowpaths and banks?

[Anonymous]

If you see this example from the YouTube, https://www.youtube.com/watch?v=o7l6Wthq-QY, you can see, that his cross-sections are the same, in ArcGIS and in HEC RAS.

[Scott Miller]

It does not look like there are very many vertices on the TIN. The number of points my ArcGIS defaults to is 1,5000,000. With not very many vertices, the resulting cross section will be very angular.

Take a look at the vertical and horizontal units on the cross section. GeoRAS may be having difficulty with the vertical exaggeration.

[Author]

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