openscope

Table of Contents
Terrain Generation
Terrain Generation (QGIS 3.4+)
- Initial setup (QGIS 3.4+)
Manual generation of river water polygons

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:

Loads the airport.json files
Automates the terrain generation process described above
Generates water polygons from the NOAA’s Global Self-consistent, Hierarchical, High-resolution Geography Database (GSHHG) database.

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:

The qgsopenscope repository
Video - Installing and using the QgsOpenScope plugin for QGIS
Video - Reshaping water polygons to match the video map
Video - Adding River Polygons to openScope terrain

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:

Generate the terrain using the qgsopenscope plugin This will generate the airspace an terrain for the current airport data.
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.
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

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.
Select the features that you want to use
Paste the features as a new Temporary Scratch Layer (Ctrl+Alt+V) and call it “Rivers”
Hide all the “WDBII*” layers (we don’t want to accidentally modify them)
Toggle editing on the “Rivers” layer and select all the features.
Select all the segments for each river, and use the Merge Selected Features tool.
Use the Simplify Features tool, set the tolerance to 0.0005 and select Map Units.
Toggle editing and save any changes.

Convert the rivers to polygons

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

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

Merge all the rivers into the water layer

Copy all the new river polygons into the terrain or water layer.
Toggle editing on the “Water” layer
Select all the rivers, and use the Modify Attributes tool to ensure each polygon’s elevation attributes is 0
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.

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