docs: add the RaCo-ALIKED ONNX/TensorRT matcher exports

README.md

@@ -41,3 +41,45 @@ fraction of the latency. ICCV 2023.
     year    = {2023}
 }
 ```
+
+## ONNX / TensorRT exports for vision-rt
+
+Alongside the PyTorch checkpoints above, this repo holds the **LightGlue+ matcher for
+RaCo-ALIKED features** as a standalone ONNX graph plus prebuilt TensorRT engines, used by
+[`vision-rt`](https://github.com/kornia/vision-rt)'s `vrt-lightglue` crate. These are the
+ONNX/TensorRT form of `raco_aliked_lightglue.pth` — not a new set of weights.
+
+```
+normalized_keypoints (2P,1,K,2)   f32   long-edge normalised
+descriptors          (2P,1,K,128) f32   L2-normalised
+  -> matches0 (P,K) i32   index into image 1, or -1 if unmatched
+  -> mscores0 (P,K) f32   match confidence in [0,1]
+```
+
+The matching extractor half lives in
+[`kornia/raco-aliked`](https://huggingface.co/kornia/raco-aliked); both halves must come
+from the same `kN` export, since `K` is baked into each.
+
+**Why a split graph.** Upstream
+([fabio-sim/LightGlue-ONNX](https://github.com/fabio-sim/LightGlue-ONNX)) publishes only a
+fused extractor+matcher graph, which can match only the two images handed to it in a
+single forward pass. Splitting the matcher out means descriptors extracted at *any* time —
+from a map, a relocalization database, a keyframe store — can be matched against a live
+frame. Cutting upstream of LightGlue's `NonZero` compaction also removes the graph's only
+data-dependent shapes and its int64 output.
+
+**Matching cost is O(K²)**, so unlike the extractor it gets rapidly worse with K. On a
+Jetson Orin Nano (MAXN_SUPER, TRT 10.3.0.30, fp16, one pair): **7.9 ms** at k512,
+**21.6 ms** at k1024, **126.5 ms** at k3072. Extraction moves the other way (the RaCo
+ranker is bypassed at K≥3072), so pick k512 if you match every frame and k3072 if
+extraction dominates.
+
+**Engines are machine-locked** to the exact TensorRT version and GPU architecture they were
+built for (`trt10.3.0.30`, `sm87` — JetPack 6 on Orin), and to the shape profile they were
+built at. Elsewhere, build from the ONNX; `vrt-hub` does it automatically.
+
+**Licences.** The ONNX/engine files are derived works combining LightGlue (Apache-2.0),
+RaCo (Apache-2.0) and ALIKED (**BSD-3-Clause**) weights. BSD-3-Clause requires its
+attribution to be reproduced in redistributions in binary form, which these files are — see
+[`LICENSE-NOTICE.md`](LICENSE-NOTICE.md). That notice is absent from the upstream export
+repo and is reproduced deliberately.