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nst
New Contributor
Posts: 6
Registered: ‎10-25-2017

Spatial Intersection with shape files - z-coordinate not transferred

Hello team,

one of our customers would like to make a spatial intersection with two shape files (operator = touched). One file contains only values for the X and Y coordinates, the other file contains values for X, Y and Z coordinates. ANSI is used as TEXT ENCODING. Unfortunately, not all values for the z-coordinate are taken into account when cutting. This means, for example, that for some polylines the values for the z-coordinate are taken over and for other lines not.
Does anyone know this problem and has a solution for this?


Thanks for your help.

Technical Evangelist
Technical Evangelist
Posts: 255
Registered: ‎02-03-2016

Re: Spatial Intersection with shape files - z-coordinate not transferred

I do not have any definitive answer, but let me share some thoughts that may relate.

 

  • GeoMedia has (only) a 3D model in which each vertex has X,Y,Z.  Data brought in from a 2D data source is given Z values of zero for each vertex, and this is the way the data is represented throughout GeoMedia.  So although you (as a user) know that one shapefile has meaningful Z values and the other does not, GeoMedia does not know that.
  • The spatial intersection capability uses topology to accomplish its job.  Although it is a 2D topology fundamentally, we do attempt to retain Z values when possible.  However only one Z value is retained for any given node in the topology, so if multiple features converge at the same node with different Z values, only one will be preserved.  I can't recall how that decision is made.
  • How that decision is made is probably important to you, since Z values pulled from one set of input features will have zeroes, while others will have non-zero values.  This may be why you see different scenarios for different lines.

Hal

 

Staff
Posts: 147
Registered: ‎02-02-2016

Re: Spatial Intersection with shape files - z-coordinate not transferred

The Z value assignment is taken from the first topo element found/encountered using a scanline approach (top down, left to right).  Although the values are assigned logically, you won't be able to take advantage of the logic to control the Z assignment.   This may be an appropiate topic for product ideas.

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