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Slope lines from segmented digital elevation model - after upgrade to QGIS 2.12.1

Dec 19, 2015

I mentioned previously that I used QGIS to draw lines in the direction of slope, where I had a segmented layerstack which included elevation, slope, aspect and 2 curvature layers (longitudinal and cross-sectional). This was done with RSGISlib in a similar way to my Mars work.

There was an bug with QGIS 2.12 that meant the plotting of arrows didn't work but with QGIS 2.12.1 this seems to be working again. It still takes a long time to render with the SVG marker, even with 32GB RAM and a quad-core system.

Here are a few examples:

Truro area in Cornwall. The slopes are marked with arrowed lines, with steeper slopes marked more thickly, and red for convex, and blue for concave slopes.

A closer zoom into the city.
Around Falmouth, including Pendennis Head
Falmouth again, with grayscale elevation.

Aberystwyth, Ceredigion, Wales:

I show here several QGIS screenshots, at 1:10000 or larger scale, since the rendering of the arrows becomes very slow beyond 1:10000.

Ynys Las and part of Borth Bog (Cors Fochno). This is mainly a flat area so most segments do not have lines shown.
Borth itself, a little to the south
Clarach Bay, and Wallog, and Bow Street

Aberystwyth town and main university campus are here shown, along with Pendinas hillfort, Penparcau, and Llanbadarn Fawr.

Cadair Idris - a textbook glacial landscape

Showing the arrows downslope only.

Adding in the slope parallell lines but making the arrowheads smaller.

At 1:20000 this takes a long time to render on the map canvas in QGIS.
A version with only the lines renders much faster.

Using contours instead of shading to indicate elevation.

Ebrenn y'n nos mis Kevardhu 2015

Dec 16, 2015

The folllowing is my 'Ebrenn y'n nos' (Sky at night in Cornish) contribution that I prepared December 2015. Apologies that I haven't managed to get this recorded for Radyo an Gernewegva and it will be too late now for it to be current.

Very late I know, but here is a relatively low quality recorded version. I have had trouble with noise using my own external microphone which I have tried to suppress with filtering in Audacity.

Ottomma rann nowydh kevres "Ebrenn y'n nos" mis-Kevardhu.

Y'n mis ma, yma'n dydhyow an berrha a'n vlydhen. Yma howlsav an gwav 22a mis-Kevardhu pan vydh an howldrevel diworth Kardhinan 0817 ha'n howlsedhes 1617.
Diworth Pluwvaria yn Syllan yth yns an termynow 0821 ha 1626 (pymp mynysenn moy a dhydh) ha diworth Marwyn ogas dhe Bud yns i 0819 ha 1614 (pymp mynysenn le a dhydh). Kardhinan a'n jeves dorles arbennik drefenn eus 8 our poran ynter howldrevel ha howlsedhes.

2000 blydhen kyns Krist, yth o an dydh dhe'n howlsav gwav nebes berra, 0830-1623. Diworth Syllan (49°52') yth esa an jydh 0834-1634 (6ves mis-Genver 2000KK). An le usi an dydh howlsav gwav eth our a-hys a wrussa movya dhe'n north dres an kansvlydhynyow. Yma gans Kardhinan dorles 50°30'.

Yma an planet Yow gweladow y'n ebrenn bora an mis ma, ughel y'n soth kyns an howldrevel. Ev a sev a-dro dhe hanternos, hag a dhrehedhes y vann ughella our po dew kyns an howldrevel.
Meurth ha Gwener a wra omdiskwedhes nebes diwettha. Yow a vydh a-dherag an howl 8ves mis-Meurth 2016, ha Meurth a vydh a-dherag an howl 22a mis-Me 2016.

Yma Gwener yn Libra, nag yw hi labelys. 19ves mis-Kevardhu, 7 eur myttinweyth.

Yma kowas sterennow-koedha an mis ma. Yma an 'Geminids' gweladow diworth 7ves-16ves mis-Kevardhu, ha'ga bann yw 14ves mis-Kevardhu. Nosow an 13ves ha'n 14ves a vydh da aga gweles mars yw an ebrenn kler.
Yma an 'Geminids' temmigow doust ha bilennow diworth planetik Phaethon. Y hyll bos bys dhe 80 anedha gwealdow pub our ha traweythyow moy martesen. Yma an niver ughella dhe 1 po 2 eur, mes nyns yw res gortos difun mar dhiwedhes, ymons i gweladow a-hys an nos.
Gwel dhe gavoes moy a gedhlow.

An loor: kwartron diwettha yw 3a mis-Kevardhu, loer nowydh yw 11a mis-Kevardhu, kynsa kwartron yw 18ves, loer leun yw 25ves – dydh Nadelik. Moy a-dro dhe'n loer leun Nadelikl omma:
Yma an lowr nowydh dhe'n bann 'Geminids' ha possybl vydh kavoes erbrenn tewl ragdha.

Yma New Horizons ow mos yn-mes an system howlyek mes kyns henna ev a wra treusnija taklenn grogys Kuiper 2014 MU69 dhe Dy' Kalann 2019.
Data diworth New Horizons a dhiskwedhas 'loskvenydhyow rew' war Bluton, i a welas menydh gans toll orth an penn. Rag an nowodhow a-dro dhodho gwra gweles orth

Onan an gwella 'resolution' imajys o Bluton dre New Horizons. Gwiasva John Hopkins University, Applied Physical Laboratory

Bys nessa prys ha Nadelik Lowen.

Mars mid-latitude glaciers map index page

Nov 17, 2015

Here is a graphical index to my posts on the mid-latitude Souness GLFs. These are the objects discussed in Souness et al. 2012. They are shown in white here but not really visible at this scale. Each box is a link to my previous blog post on that zone. The various Mars Express HRSC tiles where a digital elevation model is available are outlined in black. I have used an equicylindrical coordinate system with standard parallel 40°.

The yellow crosses show the prospective landing sites for ExoMars, the thick one is the primary landing site of Oxia Planum for a 2019 landing, the two other crosses for Mawrth Vallis and Aram Dorsum which remain in contention for a delayed 2021 landing.

Hopefully the boxes are appearing in the right places.

See also a larger version (1600x800px) of this index page at my website.

Phlegra Montes

Nov 14, 2015

In the final instalment of my posts giving a summary of the northern mid-latitudes of Mars, I will present the Phlegra Montes area, in the easternmost part (if you're working with -180 to 180° longitudes as I am) of the northern hemisphere.

This area has some special interest taken in it lately, with a paper giving evidence for wet-based glaciation in the area written recently  Eskers in a complete, wet-based glacial system in the Phlegra Montes region, Mars (Gallagher and Balme 2015). link

The HRSC tiles h1423, h1628 and h1412 overlaid on MOC image mosaic and colourised by elevation.
I use the same elevation colour ramp for HRSC tiles as in Utopia Planitia as follows:

MOLA elevation alone.

Hillshaded MOLA elevation.

Northernmost region:

With classifier functions for 'head' and 'extent'.

Two Souness GLFs are just missed by the HRSC coverage.

A little further south:

Relatively few Souness GLFs are found in this area.

In this region the GLFs are often found around relatively small isolated mesas, though many some of these do not host a catalogued GLF and look similar to the classifier.

Close up of region around Souness 167 and 168.

HRSC nadir image.
With classifier function.


Central region of Phlegra Montes:

A number of Souness GLFs are found in this area.
With classifier function
Zooming in a bit more

A little to the south of the previous image

Further to the south again

Southern Phlegra Montes area

This covers the same region as the study areas of the Gallagher and Balme 2015 paper. They postulate wet-based glaciation in this area, arguing this was made possible by geothermal heat flux.
Nadir images.
With the classifier.
The detailed study area from the paper at ~163°E, 32.5°N, with a lineated valley fill at the left and the postulated wet-based glacial forms including sinuous ridges near the centre of this image.

HRSC nadir image
With the classifier.

Utopia Planitia

Nov 14, 2015

Most of the North of Mars is covered by a low, flat plain.

As such, there are few Souness GLFs, these being found in the walls of craters.

Here is the area of part of Utopia Planitia, north of the shield volcanoes Elysium Mons and Hecates Tholus.

I had originally titled this 'Elysium Planitia' which is in fact in another location south of the Elysium Mons massif. The URL will continue to reflect that.


Screenshot from Google Earth showing colourised hillshaded MOLA elevation


A small number of Souness GLFs are found inside craters in Utopia Planitia.

Elevation colour ramp used for HRSC tiles in this area.

Hillshaded MOLA elevation.

MOLA elevation colour ramp.

 Four HiRISE anaglyphs overlap or are in the vicinity of Souness GLFs:

Zooming into the area covered by HRSC tiles h1526 and h2878.

Zooming in further to several areas of interest:

Crater at 116°E, 39°N containing 3 Souness GLFs, with HiRISE anaglyph coverage of one of them. HRSC tile h1526 nadir image with the classifier results.

3D anaglyph PSP_007884_2195
A crater further north in tile h1526 at 43°N without any catalogued Souness GLFs, though there looks to be remnants of some kind of flow features.

Classifier results show topography favoured for glaciers.
Google Earth screenshot with HiRISE CTX imagery of crater containing Souness 193 which is not covered by any HRSC DTM tiles. The HiRISE anaglyph referenced earlier covers a portion of the eastern wall.
Kufra Crater at 120°E, 40°N. (HRSC tile h2878 nadir image)

Bayesian classifier results (note DTM is only at 250m resolution).
Google Earth screenshot of HiRISE CTX imagery of Kufra crater.

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