Add convenience methods to load json data and generate WCS objects.

Author: aMarcireau

.gitignore

@@ -4,3 +4,4 @@ astrometry_cache
 build
 wheelhouse
 __pycache__
+test/solution.json

README.md

@@ -151,12 +151,7 @@ solver = ...
 solution = ...
 
 if solution.has_match():
-    wcs = astropy.wcs.WCS(
-        astropy.io.fits.Header(
-            astropy.io.fits.Card(key, value[0], value[1])
-            for key, value in wcs_fields.items()
-        )
-    )
+    wcs = solution.best_match().astropy_wcs()
     pixels = wcs.all_world2pix(
         [[star.ra_deg, star.dec_deg] for star in solution.best_match().stars],
         0,
@@ -485,9 +480,15 @@ class Solution:
     def has_match(self) -> bool: ...
 
     def best_match(self) -> Match: ...
+
+    def to_json(self) -> str: ...
+
+    @classmethod
+    def from_json(cls, solution_as_json: str) -> Solution: ...
+
 ```
 
-`matches` are sorted in descending log-odds order. `best_match` returns the first match in the list.
+`matches` are sorted in descending log-odds order. `best_match` returns the first match in the list. `to_json` and `from_json` may be used to save and load solutions.
 
 ## Match
 
@@ -502,6 +503,8 @@ class Match:
     stars: tuple[Star, ...]
     quad_stars: tuple[Star, ...]
     wcs_fields: dict[str, tuple[typing.Any, str]]
+
+    def astropy_wcs(self) -> astropy.wcs.WCS: ...
 ```
 
 -   `logodds`: Log-odds (https://en.wikipedia.org/wiki/Logit) of the match.
@@ -513,6 +516,8 @@ class Match:
 -   `quad_stars`: The index stars subset (usually 4 but can be 3 or 5) used in the hash code search step (see https://arxiv.org/pdf/0910.2233.pdf, 2. Methods).
 -   `wcs_fields`: WCS fields describing the transformation between pixel coordinates and world coordinates. This dictionary can be passed directly to `astropy.wcs.WCS`.
 
+`astropy_wcs` generates an Astropy WCS object. See [Calculate field stars pixel positions with astropy](#calculate-field-stars-pixel-positions-with-astropy) for details.
+
 ## Star
 
 ```py
@@ -567,7 +572,7 @@ def batches_generator(
     ...
 ```
 
-- `batch_size` sets the size of the generated batches.
+-   `batch_size` sets the size of the generated batches.
 
 `batches_generator` returns a slices generator compatible with `SolutionParameters.slices_generator`. The slices are non-overlapping and non-full slices are ignored. For instance, a batch size of `25` over `83` stars would generate the slices `(0, 25)`, `(25, 50)`, and `(50, 75)`.
 

astrometry/__init__.py

@@ -139,6 +139,17 @@ class Match:
     quad_stars: tuple[Star, ...]
     wcs_fields: dict[str, tuple[typing.Any, str]]
 
+    def astropy_wcs(self):
+        import astropy.wcs
+        import astropy.io.fits
+
+        return astropy.wcs.WCS(
+            astropy.io.fits.Header(
+                astropy.io.fits.Card(key, value[0], value[1])
+                for key, value in self.wcs_fields.items()
+            )
+        )
+
 
 @dataclasses.dataclass
 class Solution:
@@ -161,6 +172,40 @@ def to_json(self):
             match["index_path"] = str(match["index_path"])
         return json.dumps(solution_as_dict)
 
+    @classmethod
+    def from_json(cls, solution_as_json: str):
+        solution_as_dict = json.loads(solution_as_json)
+        return cls(
+            solve_id=solution_as_dict["solve_id"],
+            matches=[
+                Match(
+                    logodds=match_as_dict["logodds"],
+                    center_ra_deg=match_as_dict["center_ra_deg"],
+                    center_dec_deg=match_as_dict["center_dec_deg"],
+                    scale_arcsec_per_pixel=match_as_dict["scale_arcsec_per_pixel"],
+                    index_path=pathlib.Path(match_as_dict["index_path"]),
+                    stars=tuple(
+                        Star(
+                            ra_deg=star_as_dict["ra_deg"],
+                            dec_deg=star_as_dict["dec_deg"],
+                            metadata=star_as_dict["metadata"],
+                        )
+                        for star_as_dict in match_as_dict["stars"]
+                    ),
+                    quad_stars=tuple(
+                        Star(
+                            ra_deg=star_as_dict["ra_deg"],
+                            dec_deg=star_as_dict["dec_deg"],
+                            metadata=star_as_dict["metadata"],
+                        )
+                        for star_as_dict in match_as_dict["quad_stars"]
+                    ),
+                    wcs_fields=match_as_dict["wcs_fields"],
+                )
+                for match_as_dict in solution_as_dict["matches"]
+            ],
+        )
+
 
 class Solver(astrometry_extension.Solver):
     def __init__(self, index_files: list[pathlib.Path]):

test/test_astropy.py

@@ -0,0 +1,33 @@
+import astrometry
+
+solver = astrometry.Solver(
+    astrometry.series_5200.index_files(
+        cache_directory="astrometry_cache",
+        scales={6},
+    )
+)
+
+stars = [
+    [388.9140568247906, 656.5003281719216],
+    [732.9210858972549, 473.66395545775106],
+    [401.03459504299843, 253.788113189415],
+    [312.6591868096163, 624.7527729425295],
+    [694.6844564647456, 606.8371776658344],
+    [741.7233477959561, 344.41284826261443],
+    [867.3574610200455, 672.014835980283],
+    [1063.546651153479, 593.7844603550848],
+    [286.69070190952704, 422.170016812049],
+    [401.12779619355155, 16.13543616977013],
+    [205.12103484692776, 698.1847350789413],
+    [202.88444768690894, 111.24830187635557],
+    [339.1627757703069, 86.60739435924549],
+]
+
+solution = solver.solve(
+    stars=stars,
+    size_hint=None,
+    position_hint=None,
+    solution_parameters=astrometry.SolutionParameters(),
+)
+
+print(solution.best_match().astropy_wcs())

test/test_json.py

@@ -0,0 +1,74 @@
+import astrometry
+import logging
+import pathlib
+
+dirname = pathlib.Path(__file__).resolve().parent
+
+logging.getLogger().setLevel(logging.INFO)
+
+solver = astrometry.Solver(
+    astrometry.series_5200_heavy.index_files(
+        cache_directory=dirname / "astrometry_cache",
+        scales={6},
+    )
+)
+
+stars = [
+    [283.7181611390329, 250.9437436782978],
+    [388.9140568247906, 656.5003281719216],
+    [732.9210858972549, 473.66395545775106],
+    [401.03459504299843, 253.788113189415],
+    [312.6591868096163, 624.7527729425295],
+    [694.6844564647456, 606.8371776658344],
+    [741.7233477959561, 344.41284826261443],
+    [867.3574610200455, 672.014835980283],
+    [1178.0701325872994, 120.66335820053426],
+    [1063.546651153479, 593.7844603550848],
+    [1266.479933601124, 478.6594707983611],
+    [286.69070190952704, 422.170016812049],
+    [401.12779619355155, 16.13543616977013],
+    [393.1902113796317, 485.8601927863897],
+    [865.3547639559572, 614.3599340062373],
+    [205.12103484692776, 698.1847350789413],
+    [504.2664247977979, 214.23557044789035],
+    [-67.78648235582016, 646.7413890177716],
+    [202.88444768690894, 111.24830187635557],
+    [747.2580778813443, 116.51880571011176],
+    [339.1627757703069, 86.60739435924549],
+    [592.1438288540525, 508.6376406353861],
+]
+
+print("Solve with default parameters")
+solution = solver.solve(
+    stars=stars,
+    size_hint=astrometry.SizeHint(
+        lower_arcsec_per_pixel=1.0,
+        upper_arcsec_per_pixel=2.0,
+    ),
+    position_hint=astrometry.PositionHint(ra_deg=65.7, dec_deg=36.2, radius_deg=1.0),
+    solution_parameters=astrometry.SolutionParameters(),
+)
+
+print(f"Write the solution to {dirname / 'solution.json'}")
+with open(dirname / "solution.json", "w") as solution_file:
+    solution_file.write(solution.to_json())
+
+print(f"Read back the solution file")
+with open(dirname / "solution.json") as solution_file:
+    read_solution = astrometry.Solution.from_json(solution_file.read())
+
+if solution != read_solution:
+    assert solution.solve_id == read_solution.solve_id
+    for match, read_match in zip(solution.matches, read_solution.matches):
+        if match != read_match:
+            assert match.logodds == read_match.logodds
+            assert match.center_ra_deg == read_match.center_ra_deg
+            assert match.center_dec_deg == read_match.center_dec_deg
+            assert match.scale_arcsec_per_pixel == read_match.scale_arcsec_per_pixel
+            assert match.index_path == read_match.index_path
+            for star, read_star in zip(match.stars, read_match.stars):
+                assert star.ra_deg == read_star.ra_deg
+                assert star.dec_deg == read_star.dec_deg
+                assert star.metadata.keys() == read_star.metadata.keys()
+                for key in star.metadata.keys():
+                    assert star.metadata[key] == read_star.metadata[key]