slightly improve SRTM documentation

docs/pathprof/download_srtm.rst

@@ -84,8 +84,34 @@ to download missing tiles during run-time::
     from pycraf.pathprof import SrtmConf
     SrtmConf.set(srtm_dir='/path/to/srtmdir')
 
-Please see the `~pycraf.pathprof.SrtmConf` class reference for further
-details.
+Alternatively, if only a temporary change of the config is desired,
+one can use `~pycraf.pathprof.SrtmConf` as a context manager::
+
+    with SrtmConf.set(srtm_dir='/path/to/srtmdir'):
+        # do stuff
+
+Afterwards, the old settings will be re-established.
+
+It is also possible to allow downloading of missing *.hgt* files::
+
+    SrtmConf.set(download='missing')
+
+The default download server will be `server='nasa_v2.1'`. One could
+also use the (very old) data (`server='nasa_v1.0'`) or inofficial
+tiles from `viewfinderpanoramas.org
+<http://viewfinderpanoramas.org/>`_ (`server='viewpano'`)::
+
+    SrtmConf.set(server='viewpano')
+
+Of course, one can set all of these options simultaneously::
+
+    with SrtmConf.set(
+            srtm_dir='/path/to/srtmdir',
+            download='missing',
+            server='viewpano'
+            ):
+
+        # do stuff
 
 Download links
 ==============

notebooks/03a_path_propagation_basic.ipynb

@@ -70,7 +70,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "With pycraf it is very easy to query SRTM data for arbitrary positions. However, you will need to have SRTM data in a local directory and set the `SRTMDATA` environment variable appropriately (see installation instructions)."
+    "With pycraf it is very easy to query SRTM data for arbitrary positions. However, you will need to have to download such SRTM data, either in advance or during your session. Please see the [documentation](https://bwinkel.github.io/pycraf/pathprof/download_srtm.html) for more details."
    ]
   },
   {
@@ -673,9 +673,9 @@
  "metadata": {
   "anaconda-cloud": {},
   "kernelspec": {
-   "display_name": "Python [Root]",
+   "display_name": "Python [default]",
    "language": "python",
-   "name": "Python [Root]"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {

pycraf/pathprof/srtm.py

@@ -78,9 +78,8 @@ class SrtmConf(utils.MultiState):
         with SrtmConf.set(srtm_dir='/path/to/srtmdir'):
             # do stuff
 
-    Afterwards, the old settings will be re-established.
-
-    It is also possible to allow downloading of missing '.hgt' files::
+    Afterwards, the old settings will be re-established. It is also possible
+    to allow downloading of missing '.hgt' files::
 
         SrtmConf.set(download='missing')
 
@@ -91,6 +90,16 @@ class SrtmConf(utils.MultiState):
     also use the (very old) data (`server='nasa_v1.0'`) or inofficial
     tiles from viewfinderpanorama (`server='viewpano'`).
 
+    Of course, one can set all of these options simultaneously::
+
+        with SrtmConf.set(
+                srtm_dir='/path/to/srtmdir',
+                download='missing',
+                server='viewpano'
+                ):
+
+            # do stuff
+
     URLS:
 
     - `nasa_v2.1 <https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/>`__