Preparing Sketch-maps.
Most cave
cartographers map the floor detail and passage walls through small, hand-drawn sketches of the cave. Depending on the size of the passages, each
sketch typically has three or four shots, so there may be dozens of
sketch-maps for each survey. The image to the right is a typical
example from the 1987 survey of Fulford Cave.
These images can be scanned into a computer and then traced in a
drawing program such as Inkscape or Adobe Illustrator. They can also be
manually traced. Unfortunately,
inconsistencies in the scaling and rotation can make the process tricky
and difficult. In addition, working from dozens of small maps can make
the tracing process tedious. Finally, small errors in the sketch-maps can
put the stations in the wrong place relative to the plot of cave,
forcing the cartographer to fudge the positions manually.
To solve these problems, the Compass
sketch-map Editor allows you to scale, rotate, merge and morph the images to
match the true positions of the survey stations. To help you get
acquainted with the process, I have written this tutorial that will walk
you through the whole process.
Compass Tutorial. The Compass
sketch-map Editor is a set o special tools
designed to prepare your sketch-maps for manual tracing or digital tracing in programs like Inkscape or
Illustrator. To illustrate this process, we will walk through the process
of editing sketch-maps for
the "B" survey in Fulford cave. (Fulford is a wild cave in Colorado
that is on Forrest Service land and open to the public. The Compass
distribution contains a copy of the Fulford Cave survey data. )
Overview. The "B" survey in Fulford consists of six
sketch-maps that cover all the passage walls and floor detail. The image
to the right shows how all the images should be combined to form a
single, continuous image that makes it easy to trace the passages when
we make the final drawing.
The process consists of six steps:
1. Scale. In this step, we adjust the images so they are same
scale and at a useable size.
2. Trim. In this step, we
will trim off excess parts of the image,
so we only have the passage and floor detail.
3. Rotate. In this step we remove any residual
rotation so the passages are perfectly aligned to north.
4. Preliminary Morph. In this step, we do a preliminary
morphing of the passage. Morphing adjusts the image to match the survey station positions.
The morphing process smoothly moves the passage walls and floor detail,
so they track the survey station positions. Doing a preliminary morph on each individual image reduces the amount of
distortion produced in the final morphing step.
5. Merging. In this step we merge all the images together to
form a single, continuous bitmap.
6. Final Morphing. In this step, we morph the
combined image to match
all the station positions in the survey.
