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How to map standardized visible building damage in OSM – #BaBAR

FOR EXPERIENCED OSM MAPPERS ONLY

Following the general presentation, here are instructions to adapt and apply BAR methodology in OpenStreetMap, for Fiji after tropical cyclone Winston, starting with the western town of Ba. If you are not yet familiar with the BAR methodology, please first take the time to read: “Assessing Wind Disaster Damage To Structures”

It contains a description of concepts, and a complete set of exemples, for each structure category and damage scale, that is not repeated here, but with which you should be familiar before proceeding. The illustrated exemples from Vanuatu might hopefully not be too different from Fiji, and help to classify and evaluate many buildings.

When how to classify a structure, or how to scale damage, is not clear to you, please come and discuss it on available discussion channels convenient to you: IRC #hot channel on oftc.net, Mumble on talk.hotosm.org, HOT@openstreetmap.org mailing list, Twitter direct messages with @jgVisov (who will add you to a relevant group), etc.

In the framework of an OSM Tasking Manager, we are going to use the grid of tiles it automatically provides to share the work between mappers, and record tile comments, as our equivalent of the grid frame defined in the BAR methodology.

You are advised to split your tile if it contains any group of buildings, to be able to give full attention to the buildings it contains. A smaller initial size was not selected for the tiles only because it would have produced many small useless tiles in empty areas. It is important to take the time to do this task carefully, as best you can, and to discuss any uncertainty, as it is the first time this methodology is applied in OSM context.

Use Bing imagery as pre-event geometrical reference. You may also use other imagery if you find it useful for this task, such as Mapbox, or US Humanitarian Information Unit MapGive Digital Globe WorldView-2 imagery.

Map the roads, tracks or path that may still be missing, with usual OSM tagging.

Map all the buildings, using Bing imagery as common geometrical reference: In addition to usual tags (e.g. at least “building=…”), use the following tags to record information for the BAR method, and follow-up life cycle data management:

  • damage=[none|minimal|significant|complete] (“visible” is implicitely understood)
  • damage:structure=[light|medium|heavy]
  • damage:event=Winston
  • damage:assessment=[initial-date|revision-date] (e.g. “2016-02-26”)
  • source:damage=Pleiades 2016-02-26, CNES, Airbus DS

(combined with any other source of information, such as geolocalisable photos, separated with a “;”)

A couple of notes about the post-Winston Pleiades images layer:

  • if you add “_nir” after the date in the URL for Pleiades image, you can get another layer, with near infrared (NIR) as red, which is useful to see vegetation.
  • you could offset of the Pleiades image relative to Bing if you wish. The Ba image has been rapidly processed in an ad hoc way – that may have lost some of its positional accuracy, yet from a review, this offset doesn’t exceed a few meters.

As reminders, here are relevant extracts from the BAR study:

Assigning structure categories:

  • “Light Structures: This category, annotated with a triangle, encompasses structures that are built pre- dominantly from light material or locally sourced materials. These structures may be mobile or possess no real hard roof, in some cases, roofs are made of metal or light material; they are often small in size. As such, these structures are likely to be the most vulnerable structures in any impacted region. Examples of these types of structures can include huts, tukuls or mobile trailers.
  • Medium Structures: This category, annotated with a circle, encompasses structures that are built from semi-hard materials or mixed products. These structures have solid frames built using wood, steel or ce- ment. These type of structures are fixed and possess hardened walls and roofs which can be made out of wood or cement. Unlike light structures, these types of structures are able to withstand moderate level of wind, with no to little damage, while maintaining their structural integrity. These types of structures can be individual or multi family houses, small stores, places of worship and similar structures.
  • Heavy Structures: This category, annotated with a square, encompasses structures that are built from hard materials such as reinforced cement and steel. Infrastructure of this type is the least structurally vulnerable in any observed region. These structures are designed to withstand high level winds without receiving heavy damage or endangering the structural integrity of the structure. In many areas, these may include multiple story buildings, strip malls, hospital buildings, or public utilities.”

In the Case study for cyclone Pam impact on Vanuatu:

  • “The light structures category is assigned to traditional structures built using, cinder blocks, bricks, organic or locally sourced material with the roof built using thatch.
  • The medium structures category is assigned to single-level, small to medium sized structures built using cement walls with roofs made out of metal or prefabricated material.
  • The heavy structures category is assigned to multi-level and/or large structures built using cement walls or prefabricated material with a metal or prefabricated roofs.”

Assigning Damage Scale

“The Signal Program BAR Methodology applies a color-coded damage scale across all structure types based on repeating, visible damage patterns. Damage in the BAR scale is classified in 4 distinct categories: Green, Yellow, Orange and Red.

  • No Visible Damage: This category, classified by the color green, signifies no visible damage to the structures. In these cases, the roof is virtually undamaged and the walls, in effect, remain standing. The structure appears to have complete structural integrity and does not appear to need repair.
  • Minimal Visible Damage: This category, classified by the color yellow, signifies that some minimal vis- ible damage has been sustained. In these structures, the roof remains largely intact, but presents partial damage to the roof’s surface, with minimal exposure beneath. In oblique aerial and satellite imagery, minimal damage may be able to be observed within the structure and to the exterior walls. The structure appears to have general structural integrity but needs minor repairs.
  • Significant Visible Damage: This category, classified by the color orange, signifies that partial but ex- tensive visible damage has been sustained. In these structures, the roof is entirely damaged or missing. The walls of the structure remain upright. However, the interior wall partitions can be partially damaged. Debris inside the structure can also potentially be visible. The structure does not appear to have complete structural integrity and is in need of significant repair.
  • Critical Visible Damage: This category, classified by the color red, signifies severe visible damage has been sustained. In these structures, the roof is completely destroyed or missing, and the walls have been destroyed or collapsed. The support structures are completely leveled, and interior objects have also suf- fered visibly heavy damage or destruction. The structure does not appear to have any structural integrity and requires comprehensive reconstruction or demolition of the entire structure.

In the Case study for cyclone Pam impact on Vanuatu:

  • “The “No Visible Damage” category was applied to structure that appear virtually undamaged with no identifiable damage to the roof or the walls.
  • The “Minimal Damage” category was applied to the structures that appear to have sustained limited dam- age with only parts of the roof appearing to be either damaged or missing.
  • The “Significant Damage” category was applied to structures that appear to have sustained damage with large parts of the roof damaged or missing. These structures, however, remain standing with the walls appearing largely intact
  • The “Critical Damage” category was applied to structures that have completely lost their roofs and have sustained heavy damage to their walls. These structures have sustained massive damage to their struc- tural integrity and have largely or completely collapsed.”
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