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Four-Control-Point Projective Plane Homography
x402
Four-Control-Point Projective Plane Homography is a paid API for AI agents from detect.halowerk.com, paid per call via x402, $0.003/call, status unknown (last checked 2026-11-04).
Computes a planar projective homography from four 2D point correspondences and applies it to transform query points.
Price / call$0.003
Success—
StatusUnknown
How this service works
Register a planar drawing/image using four point correspondences.
Output
Returns a homography artifact containing the computed 3×3 projective transformation matrix derived from the four source-to-target point correspondences, along with the transformed coordinates of all supplied query points mapped through the homography into the target plane.
Example use cases
Aerial image ground plane registration
“I have four GPS-surveyed ground control points in pixel coords [(12,34),(890,22),(910,780),(8,790)] mapped to real-world coords [(0,0),(100,0),(100,60),(0,60)], and I need to project the query pixels [(450,400),(200,300)] into real-world coordinates using a projective homography.”
Document scan perspective correction
“I scanned a document and the four corners in the scan are at [(30,20),(610,10),(620,850),(25,845)] — I want them mapped to a clean rectangle [(0,0),(595,0),(595,842),(0,842)]. Can you compute the homography and transform these content marker points [(100,100),(300,400),(500,200)]?”
AR planar marker pose estimation
“My AR marker detector found four fiducial corners in camera image space at [(120,80),(320,70),(330,260),(110,275)] corresponding to the known marker template corners [(0,0),(200,0),(200,200),(0,200)]. Use the four-point homography to find where query texture coordinates [(100,100),(50,150)] project in the camera image.”
Technical details
Endpoint
POSThttps://detect.halowerk.com/v1/F-TD2000-GEO-INDUSTRY-B002/four-control-point-projective-plane-homography?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need a fast, exact projective (perspective) transformation from exactly four 2D point correspondences — the minimal set required for a full planar homography. Prefer this over affine or similarity transforms when you need to handle full perspective distortion. Ideal for image registration, document rectification, planar AR marker tracking, or any task where you know four corresponding point pairs and need to map additional query points through the same transformation.
Side effects
- Collinear or nearly-collinear control points causing a degenerate homography (singular matrix)
- Query points outside the numeric range (-1000000 to 1000000) rejected by schema validation
- Fewer or more than exactly 4 source/target point pairs causing request rejection
- Mismatched source and target arrays (different lengths) causing computation failure
- Payment failure via x402 protocol returning 402 status before computation
- Malformed 2D point arrays (wrong number of coordinates per point) failing schema validation
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| artifact | object |
Tags
x402
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