Manipulation - PowerPoint PPT Presentation

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  1. Manipulation • Modification and refinement of existing models • Components • Editing • Filtering • Merging • Data structure conversion • Sources used: • Main: Doc 21: 278-280 • Other: Docs 9, 12, DTM notes

  2. Editing • Aim: updating and error correction • Should include • Query • Add, delete, move • Change height or attribute

  3. Editing:Topology Notes • In grid DTM only height changes • In TIN DTM, local adjustment of the network topology after points inserted or deleted • Interaction by derived visual feedback simplifies the task

  4. Filtering • Smoothing • To remove details and make DTM surface smoother • To eliminate blunders • To generalise cartographic details • Enhancement • Opposite effect compared to smoothing • Surface discontinuities are emphasised while smooth shapes are suppressed • Rarely used in practice

  5. Filtering (Cont.) • Data volume reduction • To eliminate redundant data points to save storage and processing time • To reduce DTM’s resolution • As a pre-processing step in cartographic generalisation • To convert grid DTM to a TIN one

  6. Filtering: a Data Volume Reduction Technique • Define significance of points by calculating the distant between elevation of a point and its corresponding elevation in a TIN triangulated without it • Build a distance queue • Add the most significant point to the TIN • Update the queue • Continue to insert new points • End the operation when the largest distance is smaller than a tolerance

  7. DTM Joining and Merging • Some details in Doc 12: 1.4.11-1.4.12 • Join adjacent models and merge overlapping models • Joining • Grid DTM • Straightforward if the girds correspond in resolution, orientation, etc. • Otherwise needs resampling: (DTM notes: 46-50) • Coarsening • Densification • Reorientation • TIN DTM • Readjustment and connection of TIN along their borders

  8. Merging DTMs • Tasks include: • Insert elements of one model into the other • Problem: Incremental triangulation or full retriangulation • Combining data sets with conflicting attributes and varying degrees of accuracy • A complex operation; can be a MSc project

  9. Data Structure Conversion • May be in one of the following forms: • Grid-to-TIN (Filtering as stated above) • Grid-to-Contour (Doc 9: 36-38) • TIN-to-Grid (Griding) • TIN-to-Contour (Simple Interpolation) • Contour-to-Grid • simple Interpolation from TIN • Contour-to-TIN • TIN construction