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Author Topic: Mapping near vertical mountain walls  (Read 8951 times)

keg

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Mapping near vertical mountain walls
« on: April 18, 2016, 12:24:10 PM »
Hi!

I have been using Photoscan for quite a while now, but a new assignment recently got me thinking.
The job was to map a near vertical wall with our drone to produce a highly accurate pointcloud and ortophoto of a wall.

I have figured out how to get the result i want, but that means placing GCP`s on the surface of the wall, and that is quite a big challenge since it is 300 m high.

We are suppose to survey this wall over time to check for shifting/movement of the masses, and my first idea was to send a drone up to "fix" GCP`s to the wall. Not an easy task!

I`ve also considered using a high pressure canon to launch  bullets filled with Paint, but that will not give me the precise positioning of the GCP, since there will be a big random spreading of the Paint. No absolute center. The other downside to this is that the customer suspects that the masses are unstable, would`nt want the whole side to come chrashing Down.

The GCP`s will be measured into a homogenus local network with a high accuracy Totalstation.

Has anyone had any similar problems, and have come up with a brilliant solution?

Best Regards

KEG

JMR

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Re: Mapping near vertical mountain walls
« Reply #1 on: April 18, 2016, 12:57:15 PM »
A total station would give you chance to pick natural points on this rocks with very high accuracy. You can use a modern TS with built in camera like leicas's TS30 and store a snapshot of each of your natural GCP with high magnification so you can find it easy in the photoscan shots.
By the way, I would probably say that laser scanning might be a better approach because sucessive surveys taken from same fixed stations would give a much more reliable basis for stability monitoring.
given the size of this wall a Riegl vz800 laser scanner would be my recommendation.

keg

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Re: Mapping near vertical mountain walls
« Reply #2 on: April 18, 2016, 01:33:27 PM »
Thank you for the quick response JMR!:)

We actually did measure some Natural targets on the rock face With a Leica MS50, with images.
But It was very difficult to get the precise position of the target since the totalstation mesured at an angle from below, and when we flew up, the shape of our target was completly different. I did anticipate this, but this was only a first test to se what kind of result we could obtain.

I think i shuld aim for natural "corners", with three intersecting planes spread across the wall face like you suggest, similar to targetless laserscanning to get more exact center points.

My background is also from laserscanning, as i suspect yours is, and I have to say that in my opinion this is the best solution. But my customers are really keen on drone solutions, so my approach is now to scan the wall surface, fix this as the Reference for the future surveys, and do a best fit registration of the drone pointcloud or surface in a third-party software like CloudCompare or something similar.

What are youre toughts on such an approach?

Best regards

KEG




stihl

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Re: Mapping near vertical mountain walls
« Reply #3 on: April 18, 2016, 02:41:09 PM »
I'm glad I'm not you. What a hell of an assignment this is.

After thinking about your GCP issue for a bit, the only thing I could come up with is hanging GCP's (with enough weight to keep them from swinging) from a rope from the top of the wall.
By placing them at a set distance from eachother you can create a grid with the GCP's. And then use different lengths of rope to position the GCP's at different elevations so the entire wall is referenced.
Then measure in the center with your Total Station.

keg

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Re: Mapping near vertical mountain walls
« Reply #4 on: April 18, 2016, 02:50:27 PM »
Hi Stihl!

Yes, it`s quite challenging to be me at the moment;)

Thank you so much for the tip, really appreciate it!

Best regards

KEG

Dave Martin

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Re: Mapping near vertical mountain walls
« Reply #5 on: April 18, 2016, 03:09:25 PM »
hi Keg,

not exactly the same scenario, but in case it sparks any ideas:

A few years ago I was involved in a project where we needed to effectively get GCP co-ordinates onto an inclined surface which we weren't allowed to affix anything to, we had to try & use existing features, but from the TS, we couldn't really see the natural features well enough (and the features were colour-only so wouldn't have shown up in a laser/LiDAR scan).

My solution was to post a spotter with a high-power telescope who could see the feature (maybe = UAV in your situation?) and, under the direction of the spotter, paint a laser spot to highlight the natural feature to be used as the control point and then use the TS to get the co-ordinates of the laser spot on the face. We tried using the laser pointer built into the TS, but it wasn't always sufficient so ended up using an external laser to paint each point.

This might take a few iterations, given UAV battery life, you might only be able to observe one or two GCP per flight - but this way you might be able to build up a library of detailed images of each GCP from a UAV-perspective which could allow you to manually insert markers into a proper photogrammetry mission?

Dave

keg

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Re: Mapping near vertical mountain walls
« Reply #6 on: April 18, 2016, 03:27:39 PM »
Hi Dave!

Thank you so much for the tip!

Best Regards

KEG

liz

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Re: Mapping near vertical mountain walls
« Reply #7 on: February 13, 2017, 07:03:46 AM »
Hi Keg,
Wondering if you ever found a solution to this problem? I'm looking at a very similar situation and was wondering you attempted the lowering targets over the wall option?

GPC

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Re: Mapping near vertical mountain walls
« Reply #8 on: February 14, 2017, 05:55:06 AM »
I would build a special type of drone attachment that is basically a long arm with a foam X with paint lathered on to it.  I would fly the drone up the side of the mountain wall and get close enough to press the painted X aainst the wall, there by creating a target. I would repeat this to create many points. I would then user a total station with direct reflect capability to measure the center of these X targets and generate GCP coordinates.

With that said, I would NOT use a pixel matching photogrammetry software for deformation analysis.. it is NOT AT ALL ACCURATE ENOUGH.

« Last Edit: February 14, 2017, 06:08:26 AM by GPC »
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