Route-planning principles for off-track routes off ridges.

[mandragara]

Hi,

I'm curious to know how you guys go about planning off-track routes up\down from ridge-lines. I know most of it is 'get there and see what works', 'keep cutting along until you find a break in the cliff-lines etc' - however I am curious as to how others go about choosing initial sites to try.

Take the below map for example, I can see four potential routes down to choose from:

1) and 2) Convex ridges like this tend to less vegetated and therefore easier to walk down, even contour spacing lessens the likelyhood of impassable cliffs. Could potentially use waterway to cut through any small cliff lines.

3) Can utilise gentle ridge for a fair portion of the descent. Waterway seems wide and therefore potentially crossable if needed, giving two potential ways around any cliffs encountered. Wider waterway also indicates softer rock, which decreases the likelyhood of steep cliffs.

4) Descend as far as possible along the main ridge system, which one takes for granted is doable. Then descending in between the two waterways should mean the area is a bit more 'worn' and less likely to contain sharp cliffs, more likely to be a scree field. If cliffs are encountered each waterway gives two potential ways to bypass. However the main river turns sharply at this ridge line, indicating that this are of the ridge is made of rock that is harder than the rocks that used to be downstream of it, meaning that cliffs are more likely.

Does any of this sound like the reasoning you go through when looking at a topographic map? Are there any principles I am missing? Or does everyone just wing it like me!

Cheers,

Richard

[tom_brennan]

Topo maps in those areas are hopeless - 20m contours. Here's a spot near Little Capertee Creek (Newnes), where the creek coming in from the east looks like it will have a very steep waterfall. Instead, it's a walk down gully.

2021-02-07 16_58_38-NSW Bushwalking Maps.png (542.1 KiB) Viewed 19369 times

I'd generally look at the aerial photos. Shadows and the like will give you an idea of potential clifflines. Unfortunately the area that you are looking at is north facing, so no shadows. Also, the clifflines are fairly broken, so this approach is not as useful as it can be in other areas. But you can still zoom quite a lot further than this image is showing, and get a lot more details.

2021-02-07 17_04_20-NSW Bushwalking Maps.png (714.24 KiB) Viewed 19369 times

So finally I'd get a better map. For this you can turn to the new DEMs from ELVIS, and the free QGIS application. Here's a much better map of the area around your Pass 4. Red is cliff, white is easier ground, other colours are in between. Looking at your Pass 4, I'd head down the eastern creek until it gets steep, then traverse out over the spur to the western creek, and then out to the west and down to the Colo.

The Colo is fairly big clifflines, and the problems are usually at/near the bottom.

[mandragara]

Yeah I've had a lot of fun experiences with those 20m contours. Including climbing a spur that's missing from the topo map right near T3 track on accident! There were some waterways in Tambo Ck that looked like they could be dicey on the topo also, but were in fact just ramps out.

One of my reasons for wanting to do this is to not be caught at the bottom by cliffs, I've had that happen once or twice now while trying to find some new passes down and it's a bit of a pain, especially now it's summer and there aren't many tree-crowns to keep the sun off of you.

So finally I'd get a better map. For this you can turn to the new DEMs from ELVIS, and the free QGIS application. Here's a much better map of the area around your Pass 4. Red is cliff, white is easier ground, other colours are in between. Looking at your Pass 4, I'd head down the eastern creek until it gets steep, then traverse out over the spur to the western creek, and then out to the west and down to the Colo.

Your QGIS based cliff maps look amazing by the way! I've managed to get sort-of close to what you have, however I'm not quite sure how you've managed to pull this cliff data out of the DEMs.

This is what I have so far, using the NSW Govt DEMS from here: https://elevation.fsdf.org.au/

dsf.PNG (622.24 KiB) Viewed 19326 times

Any tips would be greatly appreciated!

[tom_brennan]

In QGIS, use the Slope function in the Processing Toolbox on the DEM, then style it like this:

2021-02-09 07_58_49-_Untitled Project - QGIS.png (2.7 KiB) Viewed 19215 times

I've found that to give a pretty good representation of cliffs.

For identifying passes, you obviously have to interpret it with some knowledge of the general area. And it won't necessarily identify passes that use cave systems, ledges or narrow slots, as these features may not show up from the DEM.

There's some information on creating contours and stream extraction at http://maps.ozultimate.com/wiki/nsw_lidar , but I have some more automated processes that I'll probably add when I have some time.

[ILUVSWTAS]

I fixed no.1 for you.

Attachments

[wildwanderer]

In QGIS, use the Slope function in the Processing Toolbox on the DEM, then style it like this:

2021-02-09 07_58_49-_Untitled Project - QGIS.png

I've found that to give a pretty good representation of cliffs.

For identifying passes, you obviously have to interpret it with some knowledge of the general area. And it won't necessarily identify passes that use cave systems, ledges or narrow slots, as these features may not show up from the DEM.

There's some information on creating contours and stream extraction at http://maps.ozultimate.com/wiki/nsw_lidar , but I have some more automated processes that I'll probably add when I have some time.

This is a gold mine! Thanks Tom!

[mandragara]

In QGIS, use the Slope function in the Processing Toolbox on the DEM, then style it like this:

2021-02-09 07_58_49-_Untitled Project - QGIS.png

I've found that to give a pretty good representation of cliffs.

For identifying passes, you obviously have to interpret it with some knowledge of the general area. And it won't necessarily identify passes that use cave systems, ledges or narrow slots, as these features may not show up from the DEM.

There's some information on creating contours and stream extraction at http://maps.ozultimate.com/wiki/nsw_lidar , but I have some more automated processes that I'll probably add when I have some time.

Managed to reproduce it! Amazing, thanks for the tips! I'll be using this from now on as a sanity check when planning new off-track walks. I'm now busy making maps of areas I know to see how on-point the cliff representation is, so far it seems pretty on the money though! Using Colo Pass 18 as an example.

I think I might try and work out how to get the hydrology etc on there and then see if I can export my new map as something that Avenza Maps can read and georeference, cool software this!

I fixed no.1 for you.

Cheers, however I suspect you know that from experience rather than from looking at the map

[Tyreless]

I have some more automated processes that I'll probably add when I have some time.

Hi Tom,

I'm a big fan of your other mapping tools. I have had a play with QGIS but there is a lot to learn and I haven’t worked it all out yet - it will take quite some time. I'm looking forward to your automated processes. No rush, but just to let you know that you will have an audience when you are able to share your work.

Cheers,

T (aka GG)

[rcaffin]

Now try some of those tricks in the Wollemi NP.
ROTFLMAO!
Fire trail clearly marked on the map. On the ground - that was where the thickest scrub was. A blade scrape was sometimes visible.
Gentle easy spur off the plateau down to the river. It was gentle - below the 40 m high vertical cliffs at the top.
But that is the fun of Wollemi.

Cheers
Roger

[tom_brennan]

Now try some of those tricks in the Wollemi NP.

These tricks are for the Wollemi!

[mandragara]

I'm planning to head out to the Wollemi on Sunday and put this to the test!

[mandragara]

OK follow-up: These maps work so well it's almost like cheating. I walked up\down ridges near the Colo 4 times yesterday, with three of the 4 being 'new' ones identified by this GIS software. Each one was a breeze compared to some of Bob Buck's passes. I'm astounded by how accurate they are, they even work for deciding if you should go left or right to find a way up a cliff-line. This was in the general area around\east of Mt D'Arcy.

Also why is there a cairn on that mountain *before* Mt D'Arcy and not on Mt D'Arcy itself. Bizzare.

[tom_brennan]

OK follow-up: These maps work so well it's almost like cheating. I walked up\down ridges near the Colo 4 times yesterday, with three of the 4 being 'new' ones identified by this GIS software. Each one was a breeze compared to some of Bob Buck's passes. I'm astounded by how accurate they are, they even work for deciding if you should go left or right to find a way up a cliff-line. This was in the general area around\east of Mt D'Arcy.

They'll work well in the lower Colo, with its broken clifflines and open topography. Other parts of the world can prove trickier - you have to do a bit of mental calibration for different areas. That said, adding the slope to the maps has been a major improvement. 5m contours are good, but can still hide all manner of sins!

Overall, it's super handy for pointing you in the right direction, and stopping you wasting time on fairly futile areas.

Also why is there a cairn on that mountain *before* Mt D'Arcy and not on Mt D'Arcy itself. Bizzare.

No idea. Because the views are better from Not-Mt-D'Arcy?

It's roughly on the parish boundary of Wheeny and Bowen, so could be a boundary marker or some kind of survey aid. It's pretty heavy rocks!

https://ozultimate.com/tom/bushwalking/ ... _13578.jpg

[wildwanderer]

Any chance you can add this wizardry to your maps Tom as an overlay?

[mandragara]

They'll work well in the lower Colo, with its broken clifflines and open topography. Other parts of the world can prove trickier - you have to do a bit of mental calibration for different areas. That said, adding the slope to the maps has been a major improvement. 5m contours are good, but can still hide all manner of sins!

Noted! I mostly walk in the Greater Blue Mountains area though (BMs, Wollemi and Yengo) - I'll keep this in mind if I go to different parts of the country\world.

No idea. Because the views are better from Not-Mt-D'Arcy?

It's roughly on the parish boundary of Wheeny and Bowen, so could be a boundary marker or some kind of survey aid. It's pretty heavy rocks!

https://ozultimate.com/tom/bushwalking/ ... _13578.jpg

Tom I am convinced you have been everywhere xD Have you been to every named mountain on the topo map? Genuine question haha

The view is excellent I agree. It's even more beautiful now as the canopy is unburnt, which is now a rarer sight in the Colo

[tom_brennan]

Noted! I mostly walk in the Greater Blue Mountains area though (BMs, Wollemi and Yengo) - I'll keep this in mind if I go to different parts of the country\world.

Even once you get into canyon country, the data becomes a bit trickier to interpret because of the narrow slots. But still useful.

Tom I am convinced you have been everywhere xD Have you been to every named mountain on the topo map? Genuine question haha

Haha, but nah. I'm a canyoner, so I've done a lot of trips in the western Wollemi. I've done a reasonable amount around the Colo, maybe a bit under half "the passes", but haven't even been to most of the major peaks (Mistake, Parr South, Parr West, The Island, The Maiden) - all on the to do list!

Any chance you can add this wizardry to your maps Tom as an overlay?

Not a chance - it's 50GB of raw data just for Sydney and the Blue Mountains! That would cost $$$$ to serve, assuming I could work out how to process and store it en masse.

[rcaffin]

Mistake: flat ridge, but terrible scrub. A rocky top - boulders etc. OK one year after a hot fire.
Parr South and Parr West: scrub. Not too bad. Day walk.
Colo Passes: some of the Bob Buck Passes are good for rock climbing, but often there are better routes nearby. Some of them miss the point completely. We don't post the alternates.

We have a bit of an in-joke: Colo Pass 200: 200 m of rope needed.

Cheers

[icefest]

Not a chance - it's 50GB of raw data just for Sydney and the Blue Mountains! That would cost $$$$ to serve, assuming I could work out how to process and store it en masse.

I have not even found an easy way to view it in qgis, other than only loading a 2x2km area of interest.

[mandragara]

Not a chance - it's 50GB of raw data just for Sydney and the Blue Mountains! That would cost $$$$ to serve, assuming I could work out how to process and store it en masse.

I have not even found an easy way to view it in qgis, other than only loading a 2x2km area of interest.

I'm able to merge the areas of interest into a virtual raster and then process that as a big chunk in QGIS, but there's a file limit so I can't process a ton. I can use a command to merge them all as a TIFF but the output is much larger than the .asc files that go into making it. A TIFF that covers all of the Greater Blue Mountains would be 11 terabytes or so. I'm investigating if there's a way of merging the raw .asc files.

[tom_brennan]

I'm able to merge the areas of interest into a virtual raster and then process that as a big chunk in QGIS, but there's a file limit so I can't process a ton. I can use a command to merge them all as a TIFF but the output is much larger than the .asc files that go into making it. A TIFF that covers all of the Greater Blue Mountains would be 11 terabytes or so. I'm investigating if there's a way of merging the raw .asc files.

Since this thread is heading off into techno-talk, I have created a new post in Techno-Babble: Topographic maps from DEMs in QGIS

If you want to talk QGIS and processing DEMs, I'd suggest using that thread. (I've responded to the post above there).