feat: Implement get_view_as_fits function

🥅 Improve error management for hips2fits 📝 Add hips2fits example in notebook 2 📝 Move hips2fits example from notebook 2 to notebook 11 🎨 Improve error management for hips2fit and remove hips argument to take the Aladin Lite base layer survey 🐛 Change hips2fits return type to HDUList ✨ Synchronize survey traitlets to be changed on view change 🎨 Rename hips2fits function to get_view_as_fits 📝 Update changelog docs: edit plot instructions docs: edit method docs and exceptions messages
cds-astro · Jul 31, 2024 · 719a7be · 719a7be
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   The method accepts `astropy.io.fits.HDUList`, `pathlib.Path`, or `string` representing paths (#86)
 - New way to make a selection on the view with `selection` method (#100)
 - Add selected sources export as `astropy.Table` list with property `selected_objects` (#100)
+- Add function `get_view_as_fits` to export the view as a `astropy.io.fits.HDUList` (#86)
 
 ### Deprecated
 

diff --git a/examples/02_Base_Commands.ipynb b/examples/02_Base_Commands.ipynb
@@ -192,7 +192,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "You can also add a FITS image to the view of the widget, either as a path (string of pathlib.Path object) or as an\n",
+    "You can add a FITS image to the view of the widget, either as a path (string of pathlib.Path object) or as an\n",
     "astropy HDU object."
    ]
   },

diff --git a/examples/11_Extracting_information_from_the_view.ipynb b/examples/11_Extracting_information_from_the_view.ipynb
@@ -17,18 +17,15 @@
    "cell_type": "code",
    "execution_count": null,
    "id": "initial_id",
-   "metadata": {
-    "ExecuteTime": {
-     "end_time": "2024-07-24T07:31:43.806466Z",
-     "start_time": "2024-07-24T07:31:43.804047Z"
-    }
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "from astropy.coordinates import SkyCoord\n",
     "import astropy.units as u\n",
+    "from astropy.wcs import WCS\n",
     "from astroquery.simbad import Simbad\n",
     "from astroquery.vizier import Vizier\n",
+    "import matplotlib.pyplot as plt\n",
     "\n",
     "from ipyaladin import Aladin"
    ]
@@ -37,12 +34,7 @@
    "cell_type": "code",
    "execution_count": null,
    "id": "2e62d34eb8543145",
-   "metadata": {
-    "ExecuteTime": {
-     "end_time": "2024-07-24T07:31:44.595633Z",
-     "start_time": "2024-07-24T07:31:44.580516Z"
-    }
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "aladin = Aladin(fov=5, height=600, target=\"M31\")\n",
@@ -63,12 +55,7 @@
    "cell_type": "code",
    "execution_count": null,
    "id": "84153657cb7cd837",
-   "metadata": {
-    "ExecuteTime": {
-     "end_time": "2024-07-24T07:31:46.921817Z",
-     "start_time": "2024-07-24T07:31:46.915120Z"
-    }
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "aladin.wcs  # Recover the current WCS"
@@ -86,12 +73,7 @@
    "cell_type": "code",
    "execution_count": null,
    "id": "a63f210b-3a64-4860-8e70-42a4c66378fa",
-   "metadata": {
-    "ExecuteTime": {
-     "end_time": "2024-07-24T07:31:48.369339Z",
-     "start_time": "2024-07-24T07:31:48.361272Z"
-    }
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "aladin.height = 800\n",
@@ -113,12 +95,7 @@
    "cell_type": "code",
    "execution_count": null,
    "id": "2ddc9637-b5c3-4412-8435-2302b6d86816",
-   "metadata": {
-    "ExecuteTime": {
-     "end_time": "2024-07-24T07:31:51.277841Z",
-     "start_time": "2024-07-24T07:31:51.271764Z"
-    }
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "aladin.wcs"
@@ -140,12 +117,7 @@
    "cell_type": "code",
    "execution_count": null,
    "id": "9595ae02388b245a",
-   "metadata": {
-    "ExecuteTime": {
-     "end_time": "2024-07-24T07:31:53.400986Z",
-     "start_time": "2024-07-24T07:31:53.389449Z"
-    }
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "aladin.fov_xy  # Recover the current field of view for the x and y axis"
@@ -164,12 +136,7 @@
    "cell_type": "code",
    "execution_count": null,
    "id": "bb48cb19a597e262",
-   "metadata": {
-    "ExecuteTime": {
-     "end_time": "2024-07-24T07:31:55.769334Z",
-     "start_time": "2024-07-24T07:31:55.496270Z"
-    }
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "m1 = SkyCoord.from_name(\"m1\")\n",
@@ -207,12 +174,7 @@
    "cell_type": "code",
    "execution_count": null,
    "id": "3efb33016d863bf7",
-   "metadata": {
-    "ExecuteTime": {
-     "end_time": "2024-07-24T07:31:58.508331Z",
-     "start_time": "2024-07-24T07:31:58.501683Z"
-    }
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "aladin.selection(\"circle\")"
@@ -230,41 +192,67 @@
    "cell_type": "code",
    "execution_count": null,
    "id": "cda32891dd654568",
-   "metadata": {
-    "ExecuteTime": {
-     "end_time": "2024-07-24T07:32:07.757249Z",
-     "start_time": "2024-07-24T07:32:07.746282Z"
-    }
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "aladin.selected_objects"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "c84e856d82dbde63",
+   "metadata": {},
+   "source": [
+    "## Getting the view as a fits file\n",
+    "The following method allow you to retrieve the current view as a fits file. If a `path` is given as a second argument, the fits file will be saved."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "6b0d3e2131e9faa2",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "fits = aladin.get_view_as_fits()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "020d2c7f",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "fits[0].header"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "36a996b424529c09",
+   "metadata": {},
+   "source": [
+    "Display the fits file using matplotlib:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "8327802bad8e8c87",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "wcs = WCS(fits[0].header)\n",
+    "\n",
+    "plt.subplot(projection=wcs)\n",
+    "plt.imshow(fits[0].data, cmap=\"binary_r\", norm=\"asinh\", vmin=0.001)"
+   ]
   }
  ],
  "metadata": {
-  "nbsphinx": {
-    "execute": "never"
-  },
-  "kernelspec": {
-   "display_name": "Python 3 (ipykernel)",
-   "language": "python",
-   "name": "python3"
-  },
   "language_info": {
-   "codemirror_mode": {
-    "name": "ipython",
-    "version": 3
-   },
-   "file_extension": ".py",
-   "mimetype": "text/x-python",
-   "name": "python",
-   "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython3",
-   "version": "3.11.8"
-  },
-    "version_major": 2,
-    "version_minor": 0
+   "name": "python"
+  }
  },
  "nbformat": 4,
  "nbformat_minor": 5

diff --git a/js/models/event_handler.js b/js/models/event_handler.js
@@ -129,6 +129,13 @@ export default class EventHandler {
       this.aladin.setFoV(fov);
     });
 
+    this.aladin.on("layerChanged", (imageLayer, layerName, state) => {
+      if (layerName !== "base" || state !== "ADDED") return;
+      this.updateWCS();
+      this.model.set("_base_layer_last_view", imageLayer.id);
+      this.model.save_changes();
+    });
+
     /* Div control */
     this.model.on("change:_height", () => {
       let height = this.model.get("_height");
@@ -151,12 +158,6 @@ export default class EventHandler {
       this.model.save_changes();
     });
 
-    this.aladin.on("layerChanged", (_, layerName, state) => {
-      if (layerName !== "base" || state !== "ADDED") return;
-      this.updateWCS();
-      this.model.save_changes();
-    });
-
     this.aladin.on("resizeChanged", () => {
       this.updateWCS();
       this.update2AxisFoV();

diff --git a/src/ipyaladin/widget.py b/src/ipyaladin/widget.py
@@ -8,6 +8,7 @@
 from collections.abc import Callable
 import io
 import pathlib
+from json import JSONDecodeError
 from pathlib import Path
 from typing import ClassVar, Dict, Final, List, Optional, Tuple, Union
 import warnings
@@ -205,6 +206,11 @@ class Aladin(anywidget.AnyWidget):
     # overlay survey
     overlay_survey = Unicode("").tag(sync=True, init_option=True)
     overlay_survey_opacity = Float(0.0).tag(sync=True, init_option=True)
+    _base_layer_last_view = Unicode(
+        survey.default_value,
+        help="The last view of the base layer. It is used "
+        "to convert the view to an astropy.HDUList",
+    ).tag(sync=True)
 
     init_options = traitlets.List(trait=Any()).tag(sync=True)
 
@@ -376,6 +382,39 @@ def target(self, target: Union[str, SkyCoord]) -> None:
             }
         )
 
+    def get_view_as_fits(self) -> HDUList:
+        """Get the base layer of the widget as an astropy HDUList object.
+
+        The output FITS image will have the same shape as the
+        current view of the widget. This uses `astroquery.hips2fits` internally.
+        This method currently only exports the bottom/base layer.
+
+        Returns
+        -------
+        astropy.io.fits.HDUList
+            The FITS object containing the image.
+
+        """
+        try:
+            from astroquery.hips2fits import hips2fits
+        except ImportError as imp:
+            raise ValueError(
+                "To use the 'get_view_as_fits' method, you need to install astroquery "
+                "with 'pip install astroquery -U --pre'."
+            ) from imp
+        try:
+            fits = hips2fits.query_with_wcs(
+                hips=self._base_layer_last_view,
+                wcs=self.wcs,
+            )
+        except JSONDecodeError as e:
+            raise ValueError(
+                "The FITS image could not be retrieved from the view. "
+                "This can happen when the widget is scrolled out of the "
+                "screen."
+            ) from e
+        return fits
+
     def add_catalog_from_URL(
         self, votable_URL: str, votable_options: Optional[dict] = None
     ) -> None: