Rock Sniffer's Study Notes

GeoMapApp - freeware GIS system linked to geological datasets pasted from main blog

GeoMapApp (www.geomapapp.net) is a Java tool (read : runs on any powerful-enough system) for interrogating various publicly available geological and geophysical data sets as well as your own data sets, then displaying the data together.
My current task - I wish to plot seabed terrain between West Africa and North Brazil, to show the potential for a "chain-of-beads" linkage for not-fully marine whales to cross the proto-Atlantic.
But now I'm tired.

The Brazilian archipelago has a lighthouse and research station at 0°55'00.4"N / 29°20'45.1"W ( 0.916764 / -29.345849 ) surrounded by 5 islets comprising nearly 12000 sq.m of exposed land. That is equivalent to about 120 m in diameter, and unsurprisingly, the 250m typical resolution of the bathymetry and coastlines global datasets don't show it.

That explains why I can't manually position a profile line across the islands. Which is unfortunate. Since multiple-leg profiles are not supported, I'll have to resort to a little subterfuge. Two approaches suggest themselves - manually calculating two end-points that pass over my desired point and looking at that, or constructing a profile from one point to my location then a second profile from my location to another point. The second method would allow construction of "dog-leg" profiles.


OK, now I've forgotten how to do images on the blog, and I've just trashed the last edit.

More JS permissions needed.

Now, having set up the profiles with identical horizontal and vertical scales, I could bodge those profiles together, end to end, to make a single profile, and edit the maps to show it properly on one. Do-able, but a lot of fankle. Alternatively, I can try to work out how to make a GIS "shapefile" (which is opening up a whole can of GIS worms itself) to produce the map plot, and export the two profiles as data files, merge them in a spreadsheet, and do the plot from the spreadsheet (I can also manually correct the StPeter-StPaul rocks elevation to match the 18m of record. It's below the resolution of the dataset.) That's a lot of work for a whim.

https://en.wikipedia.org/wiki/Saint_Peter_and_Saint_Paul_Archipelago
00°55′1″N 29°20′45″W