Extract elevation value from both ends of polyline?

Question

I have a network of polylines representing a stream network.

I also have a DEM.

What I want to do is calculate the gradient of each stream in the network so I need to calculate the elevation at either side of the polyline to give me an upstream elevation and a downstream elevation.

Is there a way that I can extract this data from the DEM?

Thanks for any help.

D_Hornby_ddh_uni · Answer

An alternate approach is to extract the nodes (you could use Feature Vertices To Points if you have Advanced license (ArcInfo)) then use the resulting point layer to sample the DEM using Extract Values to Points.

If you want to extract the elevation where the river is you may want to consider building a flow accumulation grid and then run your points through the snap pour point tool. It would be these cells that are used to query the DEM. This would guarantee your elevation is extracted from the DEM pixel where the river is, rather than an adjacent hill slope.

Duncan

808707 · Answer

The 3d analyst / Functional Surface / Add surface information tool will take your polyline and add info from a surface.
One of the options is "Average slope". You can only add a surface statistic for each feature (like minZ, maxZ, slope etc.) If you need finer control you would probably have to dump the line vertices out to points then add the surface information to that.
Good luck,
Neil

Great thanks Neil. I'll give it a go and see what happens!

NeilAyres · Answer

The 3d analyst / Functional Surface / Add surface information tool will take your polyline and add info from a surface.
One of the options is "Average slope". You can only add a surface statistic for each feature (like minZ, maxZ, slope etc.) If you need finer control you would probably have to dump the line vertices out to points then add the surface information to that.
Good luck,
Neil