Refer to this wiki's TopoDroid page for summary details and reasons why you might choose TopoDroid to collect cave survey data and sketches.

THIS PAGE IS UNDER CONSTRUCTION written by a PocketTopo user who currently does not use TopoDroid. So beware, misconceptions will be present

Many current applications tend to be interactive and work with and produce a ‘single object’ (in our case a single cave map). Generic examples of this are Inkscape and Microsoft Office applications where you work with a single data file to produce, say, a single drawing, textual or spreadsheet document.

Therion however processes instructions in batches (thconfig compilation files) and works best with modular data, many small parts of a project (in this case, including but not only, sketches/scraps) that can be used many times and rearranged to create a variety of outputs. TopoDroid (like PocketTopo) is interactive and works with one data file at a time (it is just faster and easier this way while we are in a cave). However TopoDroid can produce data for post-processing optimised for either approach, interactive ‘single object’, or batch processed multiple objects. ie one huge sketch/scrap or many small sketches/scraps.

Your use of TopoDroid and Therion will be most efficient and flexible if you consider the implications of this while you are sketching in the cave, and most especially before you export your data, ready to start working with Therion.

There are some differences in terminology and concepts between PocketTopo and Therion that deserve clarification.

1. Set Activity Level. The number of settings that are visible (and features that are enabled) depend on the Activity level that is set.
   To see all of the settings mentioned below, you will need to select ‘advanced’ or higher. Navigate to menu SETTINGS → Activity Level to check or adjust this setting.
2. While you are there, scroll down and, navigate to menu (SETTINGS - IMPORT/EXPORT) - Therion, and select whether you want point stations added automatically to Therion drawing th2 exports. Ticking this option will save you from having to create them manually using XTherion, although TopoDroid may not always do it perfectly.
   If you have chosen an activity level of ‘advanced’ or higher, you will also see options to;
   - put Therion map definitions before the survey data in .th files,
   - to create splay lines in .th2 files (seems like a bad idea to me, better to export an xvi file as well/instead),
   - to create estimated LRUD data at each station based on splay shots and,
   - set a Therion drawing scale factor.
   Choose these according to your preference.
3. Point Stations. Set the scale factor applied to Therion and xvi sketch exports (To change this, requires activity level set to expert).
   From the TopoDroid Main Window, navigate to menu SETTINGS – IMPORT EXPORT – THERION – Therion Scale.
   The default value is 100. A value of 200 results in th2 and xvi drawings that fit much better within the XTherion drawing editor zoom range of 25% to 400%.
4. Set the Stations Policy. This sets up the workflow that TopoDroid expects the Disto person to use when they arrive at a new survey station, and allows TopoDroid to name stations automatically. For example, ‘splays, forward leg’ matches the default PocketTopo workflow where first the splays are taken at a new station, then the forward survey leg is taken using three shots in a row.
   From the TopoDroid Main Window, navigate to menu SETTINGS – SURVEY DATA, and make your selection.
5. Loop closure. It is recommended that you keep the Loop closure set to its default setting of ‘none’. To check this, requires activity level set to expert, navigate to menu SETTINGS – CUSTOM SETTINGS - SURVEY DATA – SHOT DATA – Loop closure.
   It is better to be able to see loop misclosures in your field notes, save loop closure for Therion.
6. line drawing style. This has perhaps the most significant effect on the size and ease of handling and editing of your exported th2 files in XTherion. Navigate to menu SETTINGS – SKETCHING – LINES – line style, and select normal, coarse or bezier.
   There are a number of approaches, which entail different compromises;
   - Fine/normal/coarse all generate exported lines that have straight segments with no curvature. They tend to produce large files with very many line points that are difficult for XTherion to handle, and are difficult to edit once in XTherion, just due to the sheer number of points. You can reduce the number of points per line before export from TopoDroid with the decimation feature, or after export with the ‘simplify line’ feature in XTherion. Line segments are straight so it can look significantly different to your original sketch. XTherions ‘convert to curve’ feature can help here though.
   - Bezier stores lines in the same way that smoothed lines are stored in Therion. Therefore you get curved/smoothed lines with an optimum (small) number of points that is easy for XTherion to load and easy(er) for you to edit. However if you erase part of a bezier line in TopoDroid, then it may erase a larger chunk than you would like. You can store lines of all four types in the same sketch file, but that is probably an awkward workflow.
   There are also two settings that affect the Bezier line creation, ‘interpolation accuracy’ [1.0] and ‘bezier corner threshold’ [20].
7. Sketch (origin) station When creating a new sketch, TopoDroid requests a 'station'. This is the origin station that is placed at (0,0) on the drawing page. You can read about this in the 'in-App help'. From the Help menu select the help book icon, then the .=== icon, then 15Index.SurveySketch.NewSketch for details. Choosing the same 'station' for all your sketches may allow them to be aligned properly in XTherion (in future).
   You can force TopoDroid to always suggest the same origin station. From the TopoDroid Survey Data Window, navigate to SETTINGS - Sketch Origin and tick 'Fixed sketch origin'.
8. station cross section sketches. Surveys can be set up to have ‘station’ cross section sketches either ‘private’ (specific to the sketch it is created in) or ‘shared’ (between all sketches in the survey session). This choice is made on creation of the survey, and it cannot be changed once the survey has been created.
   This does not apply to ‘leg’ cross sections. These are always private/shared (?which?). [not sure if this is particularly relevant to how TopoDroid interfaces with Therion]
9. drawing tools. You should only enable drawing tools/symbols that are supported by Therion. These are chosen via the Palette button in the TopoDroid Main Window. If you want, you can add Therion support for missing symbols by defining your own symbols with metapost.

Unless your survey is small and straight forward, you should normally draw several sketches per survey trip (file). ie each sketch becomes a Therion plan and (projected or extended) elevation scrap.

TopoDroid only shows full detail for the particular sketch you are editing, although it has features to help you visualise and work with multiple sketches:

• overview window (see full detail of all sketches in the current session, but no editing)
• sketch switch (switch to editing another sketch in the current session)
• sketch outline preview (see the outline of another sketch while editing - tap 'Sketch References' button and select 'sketch outline'. You can only choose one other sketch)
• sketch split and merge. You can use these to tidy up your data before exporting to Therion. (You must activate this functionality in Activity Level 'Tester'. From the TopoDroid Main Window, navigate to menu SETTINGS - GEEK FLAGS - SKETCHING - Sketch split/merge.
  Once set Split will be available from sketch menu 'rename/delete dialog'.
  Merge will be available in Tester mode from Sketch References 'sketch outline' dialog as above)

There are also the complimentary ThManager and Cave3D Android applications to help with visualisation of TopoDroid data.

Before exporting to Therion;

• Tidy up your survey and sketches in TopoDroid prior to transferring the exported files to your ‘Therion computer’.
• Take care that wall lines are drawn with the correct -outline (out, in or none) and orientation (tick mark points into the passage).
• Aim to do only very minor drawing edits in XTherion, such as minor movement of symbols and labels (if you subscribe to the TopoDroid philosophy of making the most of your time in the ‘cave’). Editing existing drawings is not a strength of the XTherion interface!

TopoDroid can only export one scrap per th2 file. Exporting all scraps in one file is currently under development. It will be activated if you export from the TopoDroid Overview Window. If you prefer to maximise your situational awareness and context while using XTherion, or draw many small sketches/scraps, then you should manually aggregate the exported th2 files into a single th2 file with many scraps.

Overall cave system survey, map and layout definitions can be arranged in any way you prefer, as these are unrelated to the method of gathering survey data (paper sketches, PocketTopo, TopoDroid)

Refer to this wiki's TopoDroid page for summary details and reasons why you might choose TopoDroid to collect cave survey data and sketches.