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lines z value

IanBasford

I have lines representing streams that have z values, unfortunately not all the z values flow downhill, there are points within the line that flow uphill, is there a way in python to find these points and flatten them out?

Thank You.

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NeilAyres

Good luck. Reasoned questions always accepted.....

IanBasford

Thank you all for your input, the code scripts are helpful, I had started editing Akos code to address deleting vertices, I'm not fast at python, but when I get it working will post code here.

Ian

XanderBakker

This approach will not correct Z values of existing points, but "remove" those points that have a Z value that is not below the previous Z value. This means that your output XY locations of the line will be different (it will loose details).

You may want to use a different approach as outlined here: https://community.esri.com/thread/181945-interpolate-missing-z-values-in-polyline

It interpolates the invalid Z values using the M position of the vertice on the line and using the valid Z values. You will need to adapt it a bit to recognize and mark the invalid z values.

IanBasford

Thank you Akos, much appreciated.

Ian

ÁkosHalmai

Replace "InvalidLine" to your featureclass' name. It's dirty but working.

<SPAN class="comment token">#For singlepart polylines only!</SPAN>
<SPAN class="comment token">#Polyline must be digitised downstream! (StartPoint's Z value must be higher than End Point's Z value!)</SPAN>
<SPAN class="keyword token">with</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>da<SPAN class="punctuation token">.</SPAN>UpdateCursor<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"InvalidLine"</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"SHAPE@"</SPAN><SPAN class="punctuation token">)</SPAN> <SPAN class="keyword token">as</SPAN> features<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">for</SPAN> feature <SPAN class="keyword token">in</SPAN> features<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; newarray <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>Array<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; lastZ <SPAN class="operator token">=</SPAN> <SPAN class="number token">9999999.99</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">for</SPAN> part <SPAN class="keyword token">in</SPAN> feature<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">for</SPAN> points <SPAN class="keyword token">in</SPAN> part<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">for</SPAN> point <SPAN class="keyword token">in</SPAN> points<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">if</SPAN> point<SPAN class="punctuation token">.</SPAN>Z <SPAN class="operator token"><=</SPAN> lastZ<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; newarray<SPAN class="punctuation token">.</SPAN>add<SPAN class="punctuation token">(</SPAN>point<SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; lastZ <SPAN class="operator token">=</SPAN> point<SPAN class="punctuation token">.</SPAN>Z
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; newpoly <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>Polyline<SPAN class="punctuation token">(</SPAN>newarray<SPAN class="punctuation token">,</SPAN> None<SPAN class="punctuation token">,</SPAN> <SPAN class="token boolean">True</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; features<SPAN class="punctuation token">.</SPAN>updateRow<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">[</SPAN>newpoly<SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">)</SPAN>‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

Ákos Halmai

NeilAyres

Tricky....

A python approach would be fraught with difficulties like Z this side and that of a particular point. Which is "correct"?

Do the lines at least go in the correct direction ie down stream? Not saying that you would get a programmatic solution here though.

Would be difficult in my estimation.

IanBasford

Thanks Neil, unfortunately I do not have access to the DEM, so I am looking for a vector solution.

Ian

NeilAyres

Do you have access to the original dem from which these stream lines were derived?

Because I think the best solution would be to create a hydrologically correct dem first, then derive the stream lines, using the work flow outlined here :

an-overview-of-the-hydrology-tools

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