Kaart: Building Geometry Guide
Introduction
This document will walk you through how to draw buildings from scratch using the standard tools while following established best practices for editing.
Prerequisites
For editing you will need an OSM account and the latest version of JOSM installed on your computer. A majority of the tools in this guide are from the Building tools plugin for JOSM. Familiarity with the HotKeys, how to upload and check your validator.
- JOSM Plugins(link)
- Kaart: Keyboard Shortcuts
Skill Instruction
Adding the Buildings and Editing Your Data
For simple square buildings, it is easy to push B in JOSM for the building tool. Use the building shape hotkeys ⌥ + R & ⌥ + Z | alt + R & alt + Z to change the building shape. Press ⌥ + R / alt + R to switch to rectangular buildings or press ⌥ + Z / alt + Z to switch to drawing circular buildings.
| Circular Buildings | Square Buildings |
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For more complex building shapes it is encourage to draw a way around the perimeter of the building then add the building. You can do that by following these steps:
- Press A in JOSM to start drawing.
- Add nodes to the outside perimeter of the building shape.
- Click one last time on the starting node to close the way.
- Add an appropriate building tag.
- Square the building before moving on to another object or uploading.
Note: Remember to draw the building to the building footprint. You can use the roof to defnine the shape, but make sure its final position is the footprint of the building.
Squaring the Building
Squaring will help your buildings look cleaner and match tthe satellite imagery better. Note that the orthogonalization feature in JOSM is much more sensitive than in RapiD/iD. Because of this, squaring is handled slightly differently.
Simple Squaring
If the building is fairly rectangular, select the object and hit Q to square up the feature.
Acute/Obtuse Angles
If there are any acute/obtuse angles or rounded edges on the building, like pictured below, they will need to be split from the feature. Splitting the polygon protects these angles from the Q action.
Highlight all the nodes that are not 90 degree angles and press P to split the way. There will now be several individual ways but it is still a complete polygon. |
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Select a way with square corners and press Q. Repeat this for every square section of the building. |
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Highlight all the separate ways of the feature and press C to recombine the way. |
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Squaring a Corner
| Identify the corner you would like to square. | Highlight the node to the left of the chosen node, the chosen node, and then the node to the right side. | Hit Q to square.
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If you try to square the buildings without these steps, you lose a lot of the building's accuracy.
Semi-Circle Sections
Every once in a while, a building will have a turret or edge that is not perfectly flat.
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| You'll separate these parts of the building from the rest following the same splitting steps to square a corner. |  |
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Highlight the separated section and hit O to evenly distribute the nodes along the edge. |
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Now recombine the ways by pressing C. |
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Here are the different squaring techniques in practice. You can also watch the tutorial video(link) for more details.
The Extrude Tool
One of the reasons we use JOSM for editing buildings is due to the extra tools that it can utilize. The extrude tool is one of those tools!
After you have drawn or confirmed the basic shape and squared the polygon to the best of your ability, the extrude tool(hotkey X) can be used to drag entire sides of a polygon out while keeping it parallel to the rest of the building.
Making sure the building is squared before using this tool is imperative in making sure to avoid erroneous geometry errors such as self crossing ways and tails.
| Double click to place two nodes and/or click on the way between two nodes to drag a square way out. Click on image to play gif. |
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Double click to place two nodes and Shift + Ctrl and click on the way to drag it out without creating a square but keeping it perpendicular to the polygon. |
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Shift + Ctrl and click on a node to slide it in parallel with the polygon so you don't have to re-square the polygon later; on an unsquared polygon: Shift + Ctrl and click on a way to drag it perpendicular to a chosen corner. |
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Note: Pay attention to the yellow dashed line that appears; that is your guide for what directions you can slide your extruded ways.
Shared walls should be used when independent buildings happen to share a wall or even just part of a wall. Each building should be clearly defined from the outside of the structure. Each should also have its own functions/attributes, and its own entrances and exits.
You can create a shared wall between ttwo buildings in one of two ways:
- With the building tools plugin
- With hotkeys
Building Tools Plugin
This plugin has a built in feature that allows you to connect a new building to an existing one.
To do this:
- Enable the building tool.
- Select either the corner node or part of the way of the existing building.
- Note: Your cursor icon will change depending on what you have selected; a node or a way.
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- Select the next point of your building. Repeat as needed.
- Then draw out your building shape.
Once your building has been connected to the existing building the nodes will change to squares.
Note: If your new building is next to an existing building, but doesn't connect then hold Ctrl while drawing the new building. This will prevent it from connecting to the existing building.
Using Hotkeys
To map a shared wall between existing buildings, modify their geometry where they overlap, then join the ways using J where the buildings connect. If they connect exactly at the corners, selectt both corner nodes then use M to merge the nodes into one. Always run your validator after joining the buildings to make sure there are no edges left that invalidly overlap.
MapWithAI
MapWithAI is the JOSM plugin version of Rapid. It is most useful when adding in large amounts of missing data into the map. While greatly reducing the number of features to be added by hand, it still requires human validdation as the AI has been known to make misttakees. To learn more about how to add buildings with MapWithAI refer to the MapWithAI refer to the MapWithAI Plugin for JOSM(link) document.