The `browse/` directory provides a _view_ of each data file in a commonly
used format (`PNG`), while `data/` provides the actual scientific data.
From [hrsc_eaicd.pdf](hrsc_eaicd.pdf):
> The Data Directory contains sub-directories for every orbit which is part of the data set, the diretory names are the four digits orbit number. The delivery contains level-4 data for the nadir sensor and the four color sensors. It also contains Digital Terrain Models (DTMs) with two different reference bodies [21,22]:
>
> - MOLA sphere (dt in the filename)
> - MOLA Areoid (da in the filename)
The _level-4 data_ we are talking about are PDS IMAGE objects. An IMAGE object is a two-dimensional array of values, all of the same type, each of which is referred to as a *sample*.
As IMAGE object is usually accompanied by a LABEL object which is a text file containing the IMAGE's metadata (or HEADER).
In MEX/HRSC, though, _header_ and _image_ are bound in the same (.IMG) file. (See the Appendix for a simple example to read the HEADER from IMAGE.)
For an example of accessing the `data`, see the section [Data access](#data-access), for an walkthrough `browse`, go to section [Browsing the data](#browsing-the-data).
#### Archive summary
Another important directory in a PDS archive is `index/`, in the file `index.tab` one will find the list of data records (files) in the archive. This `index.tab` provide simply the list of files -- path to the data -- and respective information about their release (version).
### Archive summary
Let's quickly summarize some information ([hrsc_eaicd.pdf) regarding the HRSC
PDS archive regarding name and structure conventions in place.
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@@ -142,9 +124,7 @@ The `BROWSE` directory mirrors/mimic the `DATA` structure.
> - improvement of orbit and attittude data [19,20]
> - generation of Digital terrain Models and Orthorectification of image data [19,20]
#### Exploring the archive
### Browsing the data
Our interest now is to access the Level-4, DTM data; Which is under
`MEX-M-HRSC-5-REFDR-DTM-V1.0/MEXHRS_2001`.
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@@ -238,12 +218,12 @@ The corresponding image (10,9) shaded relief, nadir and RGB orthophotos:

#### Data access
### Data access
Now that we browsed the images of orbit 0010, and we want `ND4`,`DT4`,`DA4`
files, we go to `DATA` directory, at the same address -- `0010/` -- to check