Saturday, 28 April 2018

"Horses for courses", part II

previous post here contrasted full professional workflows for petroleum geology students, with very simple analytical tools for a businessman looking to ascertain population density. As my subsequent posts show, I have an interest in Antarctic and Arctic maps, history and climate; you can see my case against the popular web Mercator for polar regions in this map story.

Facebook group Remembering the Franklin Expedition had an interesting post about a monument on Beechey Island, the overwintering camp of the doomed 1845 expedition seeking the Northwest passage. I found it in Wikipedia & Wikimedia and is described in detail by Parks Canada:

Beechey Island 01 1997-08-02
Mouse-over for attribution

Sleuthing

So how does one place an oblique photo like that in its geographic context, for people with geographic knowledge but not necessarily any mapping expertise? I looked for free & easy software and found two: I started with Google Earth, which can post oblique photos as overlay images. But its base imagery is pretty coarse for the large scale / close-in mapping required by an aerial photo.

Axis maps

This is an amazing piece of kit - it helps create contour maps from pre-existing global digital elevation models - and this will enhance the impression of relief on a region that is pretty flat: The Canadian Arctic Islands exist on two levels, coastal and atop 1000 ft cliffs - think of it as fjord land, where the mountains have been eroded down to almost sea level - this is a general view of the region and a detailed contour map of the island.

Google Earth view of Beechey Island, off SW corner Devon Island


Axismaps 1 m. contour for Beechy Island at Google level 14 zoom

Google Earth

 GE gives you two options: view directly in a Chrome browser, or download the app that allows you to load your own files and overlay your images. Please use the latter if you wish to do this, and the detailed workflow will be posted soon.

Oblique photo as image overlay
The oblique image above has no spatial reference, as it was taken 20 years ago before digital cameras and geo-tagging. Both Wikipedia and Parks Canada have enough images that the location and azimuth of the photo could be guessed roughly, close enough to place it on Beechey Island. The ruins are those of Northumberland House that is geo-located on Wikipedia. It's then a matter of orienting oneself on Beechey Island using Google Earth imagery and relief, and the contour maps just generated in Axismaps - load it in QGIS also free and save it as KML files to post directly in GE - while 1 m. interval are shown above for eye-candy, 10 m. contours are posted on my Google placemark, as is the photo overlay. Below, the contours 'disappearing' below imagery is a classic case of mismatched datums & projections that don't drape contours over imagery.


Beechey Isl. with memorial site to the left


GE is not great for sharing, it only offers facilities to email place-mark - please comment below if I'm wrong - so I posted them and the whole data set under CC BY-SA 3.0 on Google Drive. Also created a YouTube video of same: