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Table of Contents

Table of contents generated with markdown-toc

Terrain Generation

Introduction

This guide will show you how to generate a terrain file for any airport in openScope. This is mainly done using QGIS, a free and open source Geographic Information System. The process can be quite tedious and often frustrating, so if you get stuck somewhere, you can talk to us on Slack, where we will be happy to help you!

Initial setup (QGIS 2.18)

Install QGIS version 2.18

Download and install QGIS from the QGIS website

Note: QGIS version 3 is not compatible with the Zonal Statistics plugin.

Install Zonal Statistics plugin

  • Open QGIS and navigate to Plugins->Manage and install plugins...
  • Search for Zonal statistics plugin and enable plugin

Create a folder to dump all your files into

  • The folder should be named after the airport's ICAO code, e.g. ~/KSEA/ Note: Throughout this guide it will be referred to as ~/terrain/

Obtain elevation data

  • Go to this site and download all the tiles which cover your airport and its surrounding area
  • Extract the zip files into a new folder ~/terrain/DEM/

Obtain airspace coordinates

  • Copy all the coordinates within the airspace key of your airport file
  • Convert the coordinates to the right format using this web app (Thanks @jakcharvat for this wonderful tool!)
  • Copy the output and paste it on a new file.
  • Save the file as ~/terrain/airspace.csv/

QGIS

Build Raster

  • Go to Raster->Miscellaneous->Build Virtual Raster(Catalog)...
  • Check Choose input directory instead of files
  • For input directory select ~/terrain/DEM/
  • Check Recurse subdirectories
  • For Output file select ~/terrain/dem.vrt
  • Check Load into canvas when finished
  • Click OK

Note: After it completes, click OK on the popups and Close on the Build Virtual Raster window.

Import Airspace

  • In QGIS, go to Layer->Add Layer->Add Delimited Text Layer...

  • For File Name browse ~/terrain/airspace.csv/

  • For File Format check Custom Delimiters

  • For Geometry Definition check Well Known Text (WKT)

  • Click OK

  • Go to Vector->Geometry Tools->Polygons to Lines...

  • Input layer: airspace

  • Click Run

  • On the Layers Panel, Rename Lines from polygons to perimeter

Trim Raster

  • Go to Vector->Geoprocessing Tools->Fixed distance buffer

  • Input layer: airspace

  • Distance: 0.005

  • Click Run

  • Go to Processing->Toolbox

  • Search for Clip raster by mask layer

  • Input layer: dem

  • Mask Layer: Buffer

  • Click Run

Note: QGIS may seem frozen while the algorithm is run, but it is still running. Try not clicking anywhere on the program to ensure it does not crash.

  • Go to Vector->Geometry Tools->Polygons to Lines

  • Input layer: Buffer

  • Click Run

  • On the Layers Panel, Rename Lines from Polygons layer to clipping

  • Remove Buffer layer

Build Contours

  • Go to Raster->Extraction->Contour...
  • Input: Clipped (mask)
  • Output: ~/terrain/contours.shp/
  • Interval between contour lines: 304.8 (1000ft in meters)
  • Click OK

Note: After it completes, click OK on the popups and Close on the Contour window.

  • Go to Vector->Geometry Tools->Simplify geometries

  • Input layer: contours

  • Tolerance: 0.002

  • Click Run

  • On the Layers Panel, remove contours layer

  • Rename Simplified layer to contours

Process Contours

  • Go to Vector->Data Management Tools->Merge Vector Layers

  • Layers to Merge: perimeter & contours

  • Click Run

  • In the Processing Toolbox, seach for Polygonize tool

  • Input: Merged

  • Click Run

  • Go to Vector->Geoprocessing Tools->Clip

  • Input: Polygons from Lines

  • Clip: airspace

  • Click Run

  • In the Layers Panel, Remove Polygons from Lines layer

  • Go to Vector->Geoprocessing tools->Eliminate Sliver Polygons

  • Input layer: Clipped

  • Selection attribute: area (Note: May require changing input layer to airspace and back to Clipped)

  • Comparison: <=

  • Value: 0.00005

  • Merge selection: Largest common boundary

  • Click Run

*Note: This step can sometimes take a while to complete.

Prepare for Export

  • Go to Raster->Zonal statistics->Zonal statistics

  • Raster Layer: Clipped (mask)

  • Polygon layer: Cleaned

  • Statistics to calculate: mean

  • Click OK

  • In the Layers Panel, select Cleaned layer

  • Go to Layer->Toggle Editing

  • Go to View->Select->Select by Expression...

  • Expression: "mean" < 304.8

  • Click Select

  • Click Close

  • Go to Edit->Delete selected

  • Open Field Calculator (Button with an Abacus at the top of the screen)

  • Check Create virtual field

  • Output field name: elevation

  • Output field type: Decimal number (real)

  • Expresion: floor("mean" / 304.8) * 304.8

  • Click OK

  • Go to Layer->Save Layer Edits

  • Go to Layer->Toggle Editing

Export Terrain

  • Go to Layer->Save As...

  • Format: GeoJSON

  • File Name: ~/terrain/icao.geojson/ where icao is the ICAO code of your airport, e.g. KSEA.geojson

  • CRS: EPSG:4326, WGS 84

  • Fields to export: elevation

  • Coordinate precision: 10

  • Click OK

  • Go to Project->Save As...

  • Save as ~/terrain/icao.qgs/ where icao is the ICAO code of your airport, e.g. KSEA.qgs

  • Exit QGIS

  • Delete DEM folder from ~/terrain/

Final Steps

  • Go to the Airport Modelling Repo

  • Click Upload Files

  • Drag ~/terrain/ folder into the page.

  • Add a simple commit title

  • Check Commit directly to the master branch

  • Click Commit changes

  • Copy the ~/terrain/icao.geojson file into ~/openscope/assets/airports/terrain/

  • In the airport file, ensure has_terrain is set to true

Congratulations

If you've made it this far, you have successfully generated a terrain file for openScope. Give yourself a break now, you deserve it!

If you're having any problems while following this guide, you can talk to us on Slack, where we will be happy to help you!

Terrain Generation (QGIS 3.4+)

Initial setup (QGIS 3.4+)

Using QGIS 3.4 and above, there is now a plugin - qgsopenscope that:

Intructions on how to install and use the plugin are located in the repository, as well as some videos (no audio, but subtitled) on YouTube that demonstrate the usage:

Manual generation of river water polygons

Preamble

The GSHHG database only contains coastlines and lakes. In order to generate river polygons, the lines can be imported from the CIA World DataBank II (Rivers and Political Boundaries). If you've already downloaded the shapefiles required by the qgsopenscope plugin, then you will have these files. Otherwise, downloaded the shapefile archive, and unpack it.

Load the existing aiport terrain

There are a few ways of loading the existing terrain:

  1. Generate the terrain using the qgsopenscope plugin This will generate the airspace an terrain for the current airport data.
  2. Open the QGIS project file from the airport-modeling repository If you do this, make sure that the project airspace matches the current airport data.
  3. Add the existing aiport.geoson file into a new QGIS project. You will also need to load the airspace to determine the bounds.

Note: Ensure the project CRS is WGS84 (EPSG: 4326)

Load the WDBII rivers

This is a relatively arbitrary process and you will have to decide which rivers to include. The CIA World DataBank II (WDBII) databases contains 11 levels of waterways. Levels 1, 2 and 3 should be sufficient. The levels we're mainly interested in are:

The "fine" data should be of a sufficient quality, so add the following layers into QGIS:

  • WDBII_shp/f/WDBII_river_f_L01.shp - Double-lined rivers (river-lakes)
  • WDBII_shp/f/WDBII_river_f_L02.shp - Permanent major rivers
  • WDBII_shp/f/WDBII_river_f_L03.shp - Additional major rivers
  1. Also add the OpenStreetMap layer to the project, and use this to determine which rivers should be used. A rough rule is to include rivers at least 200m wide.
  2. Select the features that you want to use
  3. Paste the features as a new Temporary Scratch Layer (Ctrl+Alt+V) and call it "Rivers"
  4. Hide all the "WDBII*" layers (we don't want to accidentally modify them)
  5. Toggle editing on the "Rivers" layer and select all the features.
  6. Select all the segments for each river, and use the Merge Selected Features tool.
  7. Use the Simplify Features tool, set the tolerance to 0.0005 and select Map Units.
  8. Toggle editing and save any changes.

Convert the rivers to polygons

Open the Processing Toolbox (Ctrl+Alt+T), and then for each river:

  1. Select the feaures
  2. Open the Measure Line tool (Ctrl+Shift+M) to measure the width agains the OpenStreeMap layer, using the units as degrees.
  3. Open the Vector Geometry -> Multi-ring Buffer tool
  4. Use "Rivers" as the Input Layer
  5. Check the Selected Features Only box
  6. Number of Rings should be 1.
  7. Enter the measurement from Step # 1 into the Distance between Rings box.
  8. And run.

Merge all the rivers into the water layer

  1. Copy all the new river polygons into the terrain or water layer.
  2. Toggle editing on the "Water" layer
  3. Select all the rivers, and use the Modify Attributes tool to ensure each polygon's elevation attributes is 0
  4. Save changes to the layer

Tidy up the generated polygons

  • Use the Merge Selected Features tool to merge any water polygons that intersect.
  • Remove any extraneous nodes.
  • Use the Reshape Features tool to remove any segments that are outside the airspace.