# TNGOs Colony — building pilot and process

Prepared 15 September 2026. Status: preliminary footprint register and imagery feasibility review, not a completed floor/height survey.

## What has actually been prepared

- 20 real building-footprint polygons imported from Microsoft Global ML Building Footprints, frozen February 2026 release, quadkey 123301331. The feature-level acquisition dates are not supplied. The release date is not the image date.
- Pilot selection: 20 closest footprint centroids to 17.44295, 78.33490 around the Road No. 22 junction area north of Mushroom Rock Road. This is a compact pilot cluster, not an authoritative cadastral block boundary.
- Polygon IDs, approximate footprint areas, source geometry hashes, provenance and explicit unknown values for missing attributes.
- Satellite context was visually reviewed. Street View coverage was visible along nearby streets. One panorama location was inspected in three directions, dated April 2026. These are three views of ONE camera location, not three independent corroborating observations.
- 23 evidence relationships: 20 satellite context associations and 3 provisional facade associations. None of the facade-to-footprint matches has passed a second-view check. Search links on the other polygons are planned inspection links, not proof of imagery availability.
- No verified floor totals, measured building heights or legal parcel boundaries. One low-rise facade shows two apparent structural levels with an unfinished upper level; its candidate polygon association is not yet confirmed.

## Process flow

1. DEFINE THE PILOT: agree the boundary, desired reference date, height definition and floor-count convention. Keep block boundary, footprint and parcel as separate layers. Include all structures within the final boundary rather than silently omitting difficult buildings.
2. SOURCE THE GEOMETRY: import open footprints or licensed orthophotos. Record source, license, release and capture dates, horizontal accuracy and geometry hash. Obtain cadastral/municipal parcel polygons separately when available.
3. CHECK FOOTPRINTS: validate closed rings, self-intersections, overlaps, duplicates, missing/new buildings and merged roofs. A single footprint may contain several buildings, and several footprints may belong to one building. Preserve original geometry and maintain a revision table. Measure area in an appropriate metre-based CRS such as UTM 44N (EPSG:32644), or geodesically; current CSV areas are approximate local-plane calculations.
4. PLAN IMAGE COVERAGE: choose camera positions facing each accessible facade, ideally two independent positions. Record source, panorama/image ID, capture time, camera position, heading, pitch, field of view, attribution and reuse permissions. Unknown capture date stays null. Owned field photos can be archived with checksums; provider imagery should use authorized viewers/references and permitted storage only.
5. MATCH IMAGES TO BUILDINGS: use camera bearing and field-of-view intersections to propose candidate footprints. Account for occluding buildings, trees and camera-position errors; do not assign by nearest centroid alone. Visually compare facade corners, entrances, road orientation and adjacent structures. A reviewer confirms the match. Store a many-to-many relationship because one view may depict several buildings and one building needs multiple views. Store image-pixel facade outline or bounding box only where permitted; this is separate from the ground footprint polygon.
6. COUNT FLOORS: count visible structural levels from ground/stilt to roof. Store above-ground enclosed levels, stilt levels, visible basement levels, mezzanines and rooftop service structures separately. Ground is one level; G+4 means five enclosed above-ground levels. S+G+4 adds one stilt level. Do not count parapets, tanks or stair-head rooms as full storeys. Occluded tops/bases produce a minimum/range or null. Record unfinished levels separately from occupied levels. A dated Street View observation is visual evidence, not field ground truth.
7. ESTIMATE HEIGHT: prefer measured facade height or a co-registered DSM minus bare-earth DTM. Report height above local ground to main roof and rooftop additions separately. If only floor counts are available, use H = sum(level heights) + roof allowance with explicit assumptions. For an illustrative five-level building at 2.8–3.5 m per level plus 0.5–1.2 m roof allowance, the interval is 14.5–18.7 m; this is an example, not a TNGOs measurement. Stilt/commercial floors need separate assumptions. Shadow height requires acquisition time, sun elevation, terrain correction and an unambiguous shadow tip. Single uncalibrated facade photographs do not give precise metric height.
8. CORROBORATE: compare two independent views, source dates and any permit/as-built or survey records. Google Open Buildings 2.5D may provide a coarse modelled height prior, but its historical raster estimates are not individual-building ground truth. Never silently replace a newer visual observation with older model output.
9. FIELD VERIFY: recheck unclear, recently built, tall or occluded buildings; record laser/rangefinder or survey method, ground reference, roof visibility and uncertainty. Parcel ownership, setbacks and planning compliance require authoritative records and appropriate surveys.
10. QUALITY GATE AND RELEASE: two-person review of all 20 pilot records; resolve image identity before releasing floor facts. Check geometry validity, evidence referential integrity, missingness, dates and units. Publish verified, provisional and unobserved states separately. Report counts for imported footprints, confirmed image matches, complete floor counts, estimated heights, measured heights and unresolved records. Retain version history.

## Data model

- buildings.geojson: building_id, ground footprint geometry, source/version, approximate area, floor fields, height interval/method, status and nullable parcel_id.
- evidence.json: imagery reference, source date, camera position/orientation, observations and candidate matches.
- building_evidence.csv: building_id ↔ evidence_id, relationship and match status. Context links are not facade confirmation.
- Future parcels.geojson: authoritative parcel_id, survey/record reference, date and boundary confidence. Do not infer ownership boundaries from roof edges or fences.
- Future observations.csv: observation_id, building_id, evidence_id, attribute, value, units, capture date, reviewer, confidence and reason. Keep conflicting observations as separate rows.
- Future building_parts.geojson: height/floor variation within one structure; avoid assigning the tallest tower height to every wing.

## Useful additional attributes

Approximate footprint area, roof form, visible stilt parking, apparent construction stage, access frontage, visible building use (tentative), rooftop tanks/solar equipment, vegetation/occlusion, image age, change since prior imagery, and uncertainty. Gross floor area is only an estimate when footprint × floors assumes identical floor plates. Do not infer resident identity, occupancy counts, ownership, internal condition, structural safety or permit compliance from imagery.

## Acceptance criteria for a completed 20-building pilot

Every record has a valid footprint and source, an explicit parcel status, at least two independent facade views or a documented coverage exception, a confirmed image match, a floor count/range or a reason it is unknown, height method and uncertainty or null, capture/review dates and reviewer sign-off. Unobservable records remain in the denominator. No numerical local accuracy claim until an independent reference survey exists.

## Sources and usage

- Microsoft open footprints and CDLA Permissive 2.0: https://github.com/microsoft/GlobalMLBuildingFootprints . Height/confidence -1 are missing-data placeholders; they were converted to null, never to zero height. The frozen source URL is stored with each feature. Newer source releases may exist; this package is not labelled latest imagery.
- Google Open Buildings: https://sites.research.google/gr/open-buildings/ . Open Buildings is a separately licensed dataset, distinct from Google Maps satellite content.
- Google temporal model limitations: https://sites.research.google/gr/open-buildings/temporal/ . Optional future modelled height layer; not downloaded or used in these pilot heights.
- Google Maps Platform terms: https://cloud.google.com/maps-platform/terms . Production workflows need suitable rights for derived data, imagery retention and map integration. This package imports open geometry and links to Google for visual review; it does not redistribute Google imagery or trace its satellite tiles.

No existing Shaikpet report was changed.