Densify - unwanted / unexpected results

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09-09-2014 04:23 AM
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Regular Contributor

I'm using desify to increase the number of vertices in my line feature so I get evenly spaced vetices along each straight line segment.
However the densify is not giving me the control I want - it is putting in more points than I require.

Example:

     Simple 2 point line - 1918m long

     Densify - Distance method - Distance = 600m

     Result: 6 point line with vertex distance = 384m.

     Expected result: 5 point line with vertex distance = 479m

This is a very simple example but my feature contains hundreds of thousands of km of lines so I'm getting a lot more points than I want.

Why is densify making this decision?  Is there a tool that offers more control?

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Esri Esteemed Contributor

Can you provide the coordinates of one geometry, before and after?  It would be a lot easier to explain the behavior if we could see it.

- V

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Regular Contributor

Sorry I can't post example data.

Here's some more info:

  • The data covers the whole of britain and I have tried running Desify in Brit-Nat-Grid and WGS84 with similar results.
  • In Densify if I set a Distance of 'X' I expect vertices to be added to my line separated by distances as close to X as possible.  However I actually get vertices separated by distances much less than X.

How does the Densify tool decide on the separation of vertices when a DISTANCE Densification Method is used? - it doesn't seem to offer the control I require.

Is this clearer?

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Esri Esteemed Contributor

I've written my fair share of custom densification code, and have struggled to find the "best" vertex distribution algorithm, especially when using Cartesian distances with geodetic coordinates.  I've found many different options:

  • Add vertices from the FROM side until all but the last segment is at the specified distance
  • Add the average distance needed to break the shape into the needed number of parts
  • Split the first and last segments into the sizes needed to make the other segments evenly sized
  • Split the first and last segments into the sizes needed to make the other segments evenly sized and not significantly different from the length of other segments

This last methodology would explain the occasional need to add an extra vertex over those that are strictly necessary, but it's impossible to tell without the actual data (or the source  to the Densify tool).

- V

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MVP Esteemed Contributor

If the data are in projected coordinates try this toolbox I curious to see if it performs the same way as the others.  Also, certainly you can select one polyline segment where densification went wrong and share it for testing purposes.

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Esri Notable Contributor

I assuming you're using the Densify tool. According to this thread, you're seeing the expected results.

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