Accuracy Specification:

The Building Outlines contain spatial detail reflective of the visible characteristics of building outlines as seen from the source imagery. The building outlines were created by an automated method of feature extraction.

Building Outlines adhere to the thresholds stated section titled “Accuracy Specification Assessment”. A sampling methodology has been detailed to capture conformance thresholds for elements of quality that cannot be measured across the entire population of the output.

Sampling Methodology:

Some quality measurements are not feasibly executed across the full range of data delivered. In order to manage the quality of the data for the elements which cannot be globally measured across the whole population, the following sampling methodology was applied:

For every 1,000km2, an area of 50km2 was selected at random to represent a sample site. Within each sample site, a manual operator assessed all building geometries present in the Building Outline vector to ensure adherence to the thresholds stated in Section “Accuracy Assessment of Building Outline Extraction”.

Accuracy Assessment of Building Outline Extraction

Criteria and supply thresholds used for accuracy assessment:

False Negatives and False Positives, <=5%

Valid Interpretation >= 95%

Valid Geometry >= 95%

Minimum area >= 95%

False Negatives:

• Definition: The number of missing buildings that were not extracted expressed as a percentage of the number of the total buildings that should have been extracted.

• Assessment method: Within each sample site, a manual operator identifies any buildings from the source imagery with an area >= 10m2 that have not been represented in the Ecopia Building Outline vector. The number of missing buildings is to be expressed as a percentage of the number of buildings that should have been extracted.

False Positives:

• Definition: The number of excess buildings that were wrongfully extracted as a percentage of the total buildings that should have been extracted.

• Assessment method: Within each sample site, a manual operator identifies any buildings from the source imagery that should not have been in the Ecopia Building Outline vector. The number of excess buildings will be expressed as a percentage of the number of buildings that should have been extracted.

Valid Interpretation:

• Definition: The number of buildings considered having a polygonal representation reflective of the real-world building features, expressed as a percentage of all buildings delivered in the Building Outline vector.

• Assessment method: Within each sample site, a manual operator assessed all building geometries to determine whether the building has a polygonal representation reflective of the real-world building features according to the prescribed guidelines. The total count of those building geometries deemed representative within the sample sites are to be expressed as a percentage of all buildings delivered in the Building Outline vector.

Minimum Area:

• Definition: The number of buildings with an area of geometry >= 10m2 expressed as a percentage of all buildings delivered in the Building Outline vector.

• Assessment method: An automated script will be run to count the number of buildings with an area of >= 10m2 pixels. To calculate this measure, extracted polygons will be projected into an equal area projection. The number of valid buildings is to be expressed as a percentage of all buildings delivered in the Building Outline vector.

Valid Geometry:

• Definition: Number of buildings with a valid geometry expressed as a percentage of all buildings delivered in the Building Outline vector. A building polygon is consider to have valid geometry if;

o It does not overlap with other building polygons;

o It does not contain any spikes;

o It does not contain lines that are intersected with each other;

o It does not contain multiple polygons.

• Assessment method: An automated script will be run to count valid building geometries. A manual operator will then go through each of the building geometries that have been detected as invalid by the automated script and confirm the correctness of the detection. The number of valid buildings is to be expressed as a percentage of all buildings delivered in the Building Outline vector.

Guidelines for Building Outline Extraction:

The following rules were used for capturing buildings:

• Building outline corners that fall between 80 – 100degrees will be made 90degrees. This was conducted on a best effort basis.

• The correct capturing of a building outline is defined as a polygon covering 90% to 110% of the base of the visible building, as shown in the source imagery.

• When buildings are partially covered by shadows or vegetation, the correct location of building outline was inferred using prior knowledge (such as buildings normally have parallel lines, symmetric structures, and so on).

• Buildings under construction are not captured.

Standalone dwellings:

• Primary building structures are captured as separate polygons. Adjoining buildings are captured as a single polygon according to visual features such as fence lines or different roof colours.

• Extension, sunrooms, balconies, patios, and annexes are captured as part of the primary building structure.

• Permanent buildings structures such as sheds and greenhouses, not attached to the primary building structure, but larger than 10m2 should be captured as individual buildings.

• Non-permanent objects such as, caravans and trampolines should not be captured as buildings.

• Inner courtyards within buildings should be captured if resolution of imagery allows.

Townhouse :

Adjoining townhouses are not separated.

Commercial buildings:

The following rules were used for the capture of commercial buildings:

• Adjoining commercial buildings should be separate. Visual features such as color, texture or parcel data (if available) can be used to infer the separation. However, “Land-locked” buildings are not be separated.

Farmlands:

Following rules should be used for capturing commercial buildings:

• Hay bales should not be captured

• Water tanks are captured. Minimum size is 16.5m².