Update mex/hrsc docs

datasets/MEX/HRSC/README.md

-# Mars Express HRSC DTM imagery
+# High Resolution Stereo Camera
+[Scholten et al, 2005]: Scholten_etal_2005-HRSC_Data_Processing.pdf
+[Neukem et al, 2004]: Neukem_etal-HRSC.pdf
 
-HSRC data are available at different processing levels.
-As explained in [Scholten et al., 2005] (hereafter S05):
-
-* Ortho and DTM data: https://pds.nasa.gov/ds-view/pds/viewDataset.jsp?dsid=MEX-M-HRSC-5-REFDR-DTM-V1.0
-* PDS node: https://pds-geosciences.wustl.edu/missions/mars_express/hrsc.htm
-
-* HRSC user guide: https://ode.rsl.wustl.edu/mars/pagehelp/quickstartguide/index.html?hrsc.htm
+HSRC data are available at different processing levels. 
+As explained in [Scholten et al, 2005] (hereafter S05) and overviewed in [Neukem et al, 2004]:
 
 * Level-1: conversion of original data stream (transmitted to ground) to de-compressed data;
 * Level-2: radiometric correction of the image data;
 * Level-3: map projection of all data;
 * Level-4: DTMs and orthoimages.
 
-[Level-4 data products are available] at:
+We are interested in Level-4 data: DTM/DEM. In particular, data taken from
+instrument's Nadir setup; Figure [S05 Fig-1] pictures the different lines fo
+sight according to the different CCDs (Nadir represented as `ND`):
+
+![HRSC/SRC technical parameters][S05 Fig-1]
+[S05 Fig-1]: Scholten_etal_2005-Fig1_Technical_Params_HRSC_SRC.png
+
+
+## Data access
+
+The following links have further information about this dataset:
+* Ortho and DTM data: https://pds.nasa.gov/ds-view/pds/viewDataset.jsp?dsid=MEX-M-HRSC-5-REFDR-DTM-V1.0
+* HRSC user guide: https://ode.rsl.wustl.edu/mars/pagehelp/quickstartguide/index.html?hrsc.htm
+* PDS node: https://pds-geosciences.wustl.edu/missions/mars_express/hrsc.htm
+* ODE: https://ode.rsl.wustl.edu/mars/indexDatasets.aspx
 
-* ESA Planetary Science Archive (PSA)
-  * http://www.rssd.esa.int/index.php?project=PSA
-* HRSCview - joint site by FU Berlin/DLR
-  * http://hrscview.fu-berlin.de/
-* NASA Planetary Data Science (PDS)
-  * http://pds-geosciences.wustl.edu/missions/mars_express/
 
-[Level-4 data products are available]: https://sci.esa.int/web/mars-express/-/42328-hrsc-high-level-data-products-available
+### Keywords
 
-## ESA
+The attached document [hrsc_label.pdf] describes in details what we is the
+metadata set for HRSC (REFDR/DTM) data products.
+In the table below, the keyword/values particularly of our interest to select
+the data we look forward to handle.
 
-ESA provides a search interface at https://archives.esac.esa.int/psa/
-and a FTP at ftp://psa.esac.esa.int/pub/mirror/MARS-EXPRESS/HRSC/ .
+keyword | value | meaning
+--- | --- | ---
+`SPACECRAFT_POINTING_MODE` | `NADIR` | spacecraft pointing mode
 
-![HRSC/SRC technical parameters][S05 Fig-1]
 
+## Extra info
 
-[Scholten et al., 2005]: Scholten_etal_2005-HRCS_Data_Processing.pdf
-[S05 Fig-1]: Scholten_etal_2005-Fig1_Technical_Params_HRSC_SRC.png
+The following link is of a thread in USGS/ISIS forum about HRSC Nadir/DEM
+misaligned data. It is a discussion between Matt and Trent on handling data in
+ArcMap + GDAL:
+* https://isis.astrogeology.usgs.gov/IsisSupport/index.php?topic=2726.0