Derek Bristol

roundtripping

Roundtripping is the process of moving and morphing drawing elements in a drafted cave map to match changes to the survey data. As cave projects evolve there is often new survey added, which may include closing new loops, resurvey, and corrections to blunders in the old data. Blunders could include bad survey measurements, bad tie-ins, transposed numbers, etc. Cave maps that are digitally drafted using software that utilizes vector graphics, such as Adobe Illustrator or Inkscape, have the ability to automatically adjust drawing elements to match changes to the data with minimal work by the cartographer. The roundtripping process can be a little complicated and it does not always work as it should. Below is a suggested workflow for roundtripping between Compass and Illustrator.

When to roundtrip (and when not to)

Roundtripping was originally developed as a feature of Walls. It is intended to save the time, effort and often frustration involved in redrafting maps when there are changes to the survey data. Historically, when maps were drafted on mylar with pencil and pen, there was a reluctance by many cartographers to start the job until the entire cave was fully surveyed and loops met a certain quality standard. This is because fixing problems with a hand-drawn map is extremely difficult. Roundtripping may reduce this excuse, and encourages cartography to begin as soon as the survey does, and allows digital working maps to be kept up-to-date. So why wouldn’t everyone use this tool? For short caves, or caves that have very few loops (e.g. linear river caves), the data is unlikely to change, or if it does change it is easy to manually move existing drawing elements around to fit the new data. In these cases there may be no efficiency gained from the round-tripping process. The other extreme is very large cave systems with extremely complex 3-dimensional loops. Roundtripping morphs drafted elements to match a 2-dimensional projection of the cave’s line-plot. So for a plan view that has a lot of complexity, the software can’t associate drawing elements (e.g. walls, ledges, rocks) with the line-plot on only one level of the plan view. Some cartographers work around this limitation by drafting cave levels separately, and roundtripping each level individually before later bringing them all back together for a finished map. Without doing this, changes to the line-plot in a lower level could cause morphing of drawing elements in an upper level. Roundtripping is ideally suited to caves that have some complexity, but mostly in two dimensions.

Programs such as Therion and CaveWhere directly tie sketch notes or drawing elements to survey stations. As the data changes these programs automatically morph everything to maintain these associations. As a result, roundtripping isn’t required as a separate process - it’s baked in. These programs have a distinct advantage when it comes to morphing drawing elements in complex 3-dimensional caves, though they are far less capable at creating the refined graphic arts that are capabilities of Adobe Illustrator.

the roundtripping process

Drawing elements in a cave map are treated in one of three ways during the roundtripping process.

Unchanged - Drawing elements such as the map frame, title, map description, survey information, legend, north arrow, scale-bar, and copyright information are not moved or manipulated in any way during the roundtripping process. By putting drawing elements into layers that don’t have a suffix of “sym” or “shp”, the software will leave these elements unchanged.

Moved - Some drafted elements get moved or repositioned to maintain their location relative to the survey data, but those drawing elements don’t get skewed or morphed in any way. This includes any text descriptions associated with the cave itself (e.g. room names, leads, passage or route-finding descriptions, terminations, etc.), ceiling heights and pit depths, survey station names (if included on the map), cross-sections, vertical control elements (e.g. depth below or above datum), and most symbols (e.g. formations, bedrock, corrosion residue, fossils, etc.). Drawing elements that get moved but are not morphed need to be placed in layers with a “sym” suffix. This stands for symbol.

Morphed - The final category is drawing elements that get morphed by stretching, rotating, and scaling the drawing elements to fit the new line-plot data. This includes cave walls, floor and ceiling ledges, pools, floor detail outlines (e.g. sediment, mud, cobbles - if using a swatch pattern), breakdown blocks, flowstone, etc. These drawing elements need to go in layers with a “shp” suffix, which stands for shape, so that the software knows to morph these items.

In order for drawing elements to be treated correctly during the roundtripping process, the cartographer needs to place those drawing elements in the correct layers. Walls survey data management software creates a layer structure when a scaleable vector graphics (SVG) file is first exported. This contains separate layers for the line-plot, frame, walls, details, background, etc. Drawing elements should be placed in the correct layers so that they are either unchanged, moved or morphed during roundtripping. Compass data software follows a very similar process for roundtripping, and that software copies the layer structure used by Walls.