User:Pbsouthwood/Wikitravel dive site maps
Wikitravel dive site maps
Usage in article
Code [[Image:Partridge_Point_reef_map.png|400px|thumb|[http://wikitravel.org/upload/shared//1/15/Partridge_Point_reef_map.png '''Map of the reef at the dive sites at Partridge Point''']]]
Standard thumbnail size for dive site maps: width = 400 pixels. — Example shown with link to full resolution image at http://wikitravel.org/upload/shared//1/15/Partridge_Point_reef_map.png in caption. This is not preferred as it does not take the user through the attribution and licensing information:
Further text scolling alongside image is disabled by <br style="clear:both" />. This would not normally be used in the article.
Code [[Image:Partridge_Point_reef_map.png|thumb|[[Shared:Image:Partridge_Point_reef_map.png|'''Map of the reef at the dive sites at Partridge Point''']]]]
Second example is a default size thumbnail linked to the image description page on shared at http://wikitravel.org/shared/Image:Partridge_Point_reef_map.png. This gives required attribution and licensing information directly, and a single click will take you to the full resolution image:
Code [[Image:Partridge_Point_reef_map.png|thumb|[[:Image:Partridge_Point_reef_map.png|'''Map of the reef at the dive sites at Partridge Point''']]]]
Third example is linked to image in En: at http://wikitravel.org/en/Image:Partridge_Point_reef_map.png Note colon(:) in front of file name to suppress display. This also provides attribution information directly, and licensing or full resolution after one more click. However there are no apparent benefits compared to linking directly to the image description page on shared (example 2).
Standard Wikitravel map colours
Colours used on Pinnacle chart
Colours used on Partridge Point chart
Colours used on Klein Tafelberg Reef chart
Layers used on Klein Tafelberg Reef
Colours used in Coral Gardens (Oudekraal) chart
DejaVu Sans Condensed
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Wikitravel Press recommended png file size 3008 x 1709 pixels
Surveying dive sites
There are several ways to survey a dive site, The GPS track method I use is medium tech, moderate hardware cost, intermediate labour intensity, and is unaffected by visibility — results are the same in good viz or bad. It is quite interesting to return to a site you have extensively mapped in poor visibility on a day when you can actually see large sections of the structure. There is a strong and entirely understandable deja vu as you recognize structures in full size 3D that were previously only known as lines on the map and rather dim and murky shadows.
The GPS Track method
Hardware and software
The hardware is a reasonably splashproof pocket GPS in a watertight plastic box on a closed cell foam Surface Marker Buoy (SMB to divers) The float must be buoyant enough to not be pulled under at any time, and low drag. I find 8kg positive buoyancy is adequate. I use a boat-shaped float carved from an old boogie board, covered with a layer of orange PVC tarpaulin cloth for visibility and toughness.
The GPS I use is a Garmin e-trex Vista, which does the job fine when it works. It has an annoying tendency to occasionally turn itself off without any obvious reason in the middle of a survey. What is important is that the GPS records a downloadable track, and that the trackpoints should be close together, so you dont lose too much detail. The GPS unit is housed in a small transparent topped Pelican box, which is nominally waterproof, but often leaks a bit, so the GPS needs to be reasonably waterproof.
The box has a piece of soft closed cell foam with a cutout to support the GPS so it does not rattle around and bang its buttons. The float is towed at the end of a regular diving DSMB reel or spool, whichever is more convenient. I have used both and both work well. A ratchet reel is slightly more convenient, but it is no big deal.
The track is downloaded to a PC using a cable and software provided with the GPS, and unneccessary track segments edited out before transferring the tracks to Google Earth. I make a copy of the track to clipboard and use photoshop to save it as a jpeg.
It is also possible to screensave from maximum resolution on Garmin map software and use these images as background to trace the contours. It helps to first open in a bitmap editor like Photoshop and erase the background to transparent. This procedure has the advantage that the images are to a consistant scale. Mark a few waypoints at convenient Lat/Long gridpoints before screensave to help position the image on the map in Inkscape
Import the jpeg into Inkscape, scale it as needed and trace the track onto your map.
Depending on the type of dive site you may wish to draw contours, or outlines, or a combination. Positions of features can be recorded by digital camera if you set the time on the camera to exactly match the GPS. Depth profiles can be derived from a dive computer if it is also synchronised, but this can be time consuming for more than a few points. The easiest procedures are outlines and contours:
The line must be kept under tension to minimise the position error of the float. This is also proportional to speed and depth, and sea state can add noise to the signal, by moving the float as the waves pass. Wave/swell error will tend to be consistent and directional, and is surprisingly small with a low-drag float. Whenever convenient, it is helpful to get a cross check on your accuracy by measuring the same track on different days and different conditions.
You can take photos and make sketches on a grid on a slate, estimating dimensions and using a compass for directions. This is not very accurate, but can be usable. Surfacing occasionally at major landmarks and taking bearings to fix their position is feasible but not efficient.
The high tech methods mostly involve surveys from a boat using side-scan sonar, which can give really high resolution, but the equipment is expensive and sensitive to bumping into large rocks.
Single or multibeam sonar/echo sounders linked to concurrent GPS input and suitable software can produce wireframe images of as high resolution as your equipment depth resolution and your patience or finances can tolerate. These methods require reasonable smooth surface conditions and do not involve diving. I am hoping to get data from this type of survey to combine with the GPS track data when they become available.