Point Clouds and Polygons

Productive Meshes from GIS for 2D Upstream Landuse Modelling

A computational mesh which describes critical terrain features  efficiently is an essential ingredient of a numerical simulation to map and diffuse peaks of high magnitude events.

The method below is a development of the point cloud structure adopted to describe the Upper Severn Reach from Munlyn to Buttington.  It is published here as an ‘open’ iterative step towards procedure which

  • for any UK catchment upstream of communities at risk
  • describes effectively terrain & amenity infrastructure to engineer exceedance flows
  • supports riparian frictional vegetation (eg lateral and longitudinal porous ‘speed-bumps’) grown in software,
  • resolves numbers productively (budget ‘TIN‘= 10-15 points/hectare average)
  • handles model boundaries efficiently (ie simple equations/time-sets for main & tributary discharges),
  • calibrates to real/surveyed events,
  • supports online flythrough publication in real-time (for good communication to stakeholders)

For a basic 100-1000 hectare GIS, by points (for River 2D finite element engine) :-

  1. Load and crop the national Z3 (Q100) floodplain perimeter; save as area;
  2. Digitize centre line (Cline); buffer (for bank lines) to main channel width; extend by 100m at inflow, outflow and main tributaries
  3. Create lateral and longitudinal attenuation features (Lats & Longs) from bank-lines (BlineL, BlineR) to Z3 perimeter; save as Lo & La
  4. Buffer combined Lo & La (LL) in proportion to main channel and floodplain (eg LL8 and LL32)
  5. Split LL8 and LL32 (LL8L, LL8R, LL32L, LL32R) and resample to points @ 32m
  6. Resample Cline @ 32m
  7. Buffer Z3 by 32m (z332)
  8. Combine Z332 and LL32 and convert to points @ 64m (= model boundary)
  9. Raise flow ridges (LL ‘speed-bumps’) and lower Cline to bathymetry
  10. Buffer Z332LL32 by 32m for Extents and resample @ 64m (inflow, outflow and tributaries by boundary equation between Extent and Boundary)
  11. Append polygon to ‘extents’;   cut vee notch ‘canyon’ between inflow and outflow.
  12. Superimpose terrain point cloud over ‘vee-notch-canyon’ (ie retain simple productive inflow, tributary and outflow boundary conditions)
  13. This should contain and describe the terrain features to budget, but within reach of real-time resolution at 2GHz


. . . .  more





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