creating terrain models with fme - excellence center for fme · 1 creating terrain models with fme...

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Creating terrain models with FME

Knut Jetlund Norwegian Public Roads Administrationknut.jetlund@vegvesen.no

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Background

EU Noise Directive

– Calculate noise from roads with

annual daily traffic > 8000

New model and application for

noise calculation

– Nord2000 (Nordic model)

– NorStøy

Norstøy terrain model

requirements

– ESRI ASCII GRID

– 10x10m grid size

– Elevation in cm

– Integer values

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Input data

Vector data from the base map

– Elevation data, Hydrography, Constructions, Road situation, Railway data and Airport data

Format

– QUADRI

• The format for GIS/LINE, from Norkart

• FME Reader: GDMMAPPER

– File based (4 files pr dataset)

– One set of files pr theme pr municipality

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Other data

Road buffer

– The area that the terrain model shall cover

Tiles

– Grid with 5x5km squares

– Used in loops, to reduce memory usage

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Working with terrain models

Base data DEM Generation DEM

80% Data preparation

15% Interpolation

5% Final preparation

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Challenges

Memory usage

– Large data amounts

– Detailed data

– Long objects

Identifying data that represent the surface

– Remove bridges etc

Bad 3D-geometry

– No elevation

– Some vertices missing elevetaion

Integer output values

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Reducing memory usage

"Umbrella" workspaces

– WorkspaceRunner

Data preparation

– Handle theme/municipality files one by one

– Clip to Road buffer

Terrain modelling

– Generate model in tiles one by one

– Merge at the end

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The process

Data preparation

Model tiles

Terreng.gdb

(Geodatabase)

Complete model

Base data

(QUADRI)

Topg.asc

(ESRI ASCII

GRID)

*.asc

(ESRI ASCII

GRID)

Sections.mdb

- Road buffer

- GRID tiles

(Geodatabase)

Loop through themes

and municipalities

Loop through tiles

Merge tiles

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Step 1: Data preparation

Result

– Geodatabase Terrain.gdb

Features transformed into four classes

– 3D Points

– 3D Lines (contour lines)

– Breaklines

– Flat areas (lakes, parking areas etc)

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Data preparation - Filter

Features that are supposed to

represent the terrain surface

– Feature type

– Vertical level (attribute)

• Remove bridges, tunnels etc

Clip against road buffer

– Extra buffer of 500m ensure

the model close to the road

buffer edge

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Data preparation - Geometry cleaning

Remove spikes

– Critical for the model!

Remove features without elevation

Figur her!

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Data preparation - Geometry cleaning

Self intersection

Split long lines (chopper)

Generalization

– Resolution of 10x10m in the model

– generalize with 1m tolerance

Scaler and CoordinateRounder

– Elevation values in integer cm

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Data preparation - Flat areas

Flat areas:

– Lakes, ocean, parking areas etc

Calculate standard deviation for vertex elevations

Areas with standard deviation < 50cm are considered to be flat

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Data preparation - result

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Step 2: Model tiles

Result

– ESRI Ascii GRIDs pr tile

Overlap of 50m between models

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Model tiles generation

1. DEM Generator– Output: DEM Points

2. PointOnArea between DEM Points and Flat areas– 3D Forcer for points within

flat areas

3. Clip DEM Points against Tile and Road Buffer

4. CoordinateRounder– Integer values for all

coordinates

5. NumericRasterizer – Convert to raster

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Step 3: Complete model

RasterMosaicker

– Merge all model tiles into one complete model

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Quality

Given the 10x10m resolution– The accuracy of the input data is "good enough" – The best indication on the quality of the model is the age of the base

data• Man made changes in the terrain

Old data New data

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Man made change: gravel pit

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Metadata

From prepared data:

– Extract year from date updatet

– Converts to raster with Year updated as value

Convert the raster to polygons

Export to ESRI Shape

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Questions