#3286: Add Line_height as a valid attribute in v.to.db --------------------------+--------------------------------------- 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 --------------------------+---------------------------------------
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@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. -- Ticket URL: <https://trac.osgeo.org/grass/ticket/3286#comment:3> GRASS GIS <https://grass.osgeo.org>
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