[GRASS-dev] [GRASS GIS] #3286: Add Line_height as a valid attribute in v.to.db

[GRASS GIS]

#3286: Add Line_height as a valid attribute in v.to.db
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  Reporter:  geografik    |      Owner:  grass-dev@…
      Type:  enhancement  |     Status:  new
  Priority:  normal       |  Milestone:  7.2.1
 Component:  Database     |    Version:  7.2.0
Resolution:               |   Keywords:  Line_height, v.in.db, kml
       CPU:  All          |   Platform:  All
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Comment (by mmetz):

 Replying to [comment:1 mlennert]:
 > Replying to [ticket:3286 geografik]:
 > > Imported kml files that include elevation data are structured
 generally as shown below in GRASS (this is an example of a contour line):
 > >
 > > east, north: -79.7630759471, 39.0874586371
 > > DBT at corH:
 > >  Type: Line
 > >  Id: 885
 > >  Length: 275.746
 > >  Line_height: 698.602997
 > >  Layer: 1
 > >  Category: 885
 > >  Driver: sqlite
 > >  Database: /Users/sesMacBook/grassdata/KML/corH/sqlite/sqlite.db
 > >  Table: DBT
 > >  Key_column: cat
 > >  Attributes:
 > >    cat: 885
 > >    cat_: 885
 > >    tessellate: -1
 > >    extrude: -1
 > >    visibility: -1
 > >
 > > Elevation data is maintained in the Line_height field which is not a
 recognized attribute, and therefor precludes any further use of these data
 in GRASS - beyond simple display and labling.  3D analysis, for example,
 is not possible.  The suggested improvement to v.to.db would add
 Line_height to the list of attributes considered in this module so that
 the elevation data could become part of the recognized feature attributes
 and be useful in other modules.
 >
 >
 > Actually, Line_height is not a "field" in the data. v.what calculates
 the minimum and the maximum height of all the vertices of a line and
 either outputs both, or, if they are equal, only one value.
 >
 > The question this raises, therefore, is: which "height" is the most
 relevant for a line ? Should it be the mean height of all vertices ?
 Should v.to.db provide lheight_min, lheight_mean and lheight_max ?

 The correct mean height of a line is the sum of the weighted averages of
 each line segment divided by the sum of weights. The weight of a line
 segment is its 3D length.

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Ticket URL: <https://trac.osgeo.org/grass/ticket/3286#comment:3>
GRASS GIS <https://grass.osgeo.org>