bundle_adjust: mention dem2gcp

docs/tools/bundle_adjust.rst

@@ -426,9 +426,8 @@ Ground control points consist of known points on the ground, together with their
 pixel locations in one or more images. Their use is to refine, initialize, or
 transform to desired coordinates the camera poses (:numref:`ba_use_gcp`).
 
-GCP can be created with ``gcp_gen`` (:numref:`gcp_gen`), ``stereo_gui``
-(:numref:`creatinggcp`), ``gcp_gen`` (:numref:`gcp_gen`), or ``dem2gcp``
-(:numref:`dem2gcp`).
+GCP can be created with ``stereo_gui`` (:numref:`creatinggcp`), ``gcp_gen``
+(:numref:`gcp_gen`),  and ``dem2gcp`` (:numref:`dem2gcp`).
 
 File format
 ^^^^^^^^^^^
@@ -474,7 +473,7 @@ Uses of GCP
 
 One or more ``.gcp`` files can be passed to ``bundle_adjust`` as shown in
 :numref:`ba_examples`, together with one or more images and cameras, to refine the
-camera poses. 
+camera poses.  The option ``--datum`` must be set correctly to interpret the GCP.
 
 GCP can also be employed to initialize the cameras (:numref:`camera_solve_gcp`), or
 to transform them as a group, with the ``bundle_adjust`` options

docs/tools/stereo_gui.rst

@@ -611,7 +611,9 @@ file can be saved as above. See the documentation of ``ipfind``
 (:numref:`ipfind`) and ``ipmatch`` (:numref:`ipmatch`), for how to increase the
 number of matches, etc.
 
-Lastly, a non-GUI automatic approach exists as well (:numref:`gcp_gen`).
+Lastly, non-GUI automatic approaches exists as well. Two methods are supported:
+tying a raw image to an orthoimage and a DEM (:numref:`gcp_gen`), and tying a
+produced DEM to a prior DEM (:numref:`dem2gcp`).
 
 See earlier in this section for how GCP can be used.