Best workflow practice for crowdsourcing shoreline changes?

[redleg_64]

I'm working on a project that will hopefully determine the efficacy of a citizen science approach to mapping shoreline change. My task is developing a workflow that is easy enough to follow so that people without a GIS or research background can produce a research-grade product. We have the imagery collection workflow completed, and the post-processing of the imagery figured out as well. We're using Metashape for this. Developing the analysis workflow is proving to be the tricky part right now, and I'm hoping CloudCompare can offer a good solution.

For now, we're trying to see if we what data we can collect from the orthomosaics and dense point clouds. I can also work DEMs into the workflow. I have been playing around Cloud Compare and I merged point clouds of one site that were collected from imagery taken on two different dates. Frankly, I'm not sure where to go from here. I need to delineate the erosion line from the reference imagery from the erosion line from the subsequent imagery, and then measure the difference. I'm sure it would be a relatively straight forward task to import the orthomosaics into ArcGIS and measure them, but that would create an accessibility issue for folks that probably wouldn't be willing to spend money for that program. Maybe instead of merging the point clouds, a cross section comparison might work?

I'd like to keep the workflow to a level where most people can accomplish the tasks in a reasonable amount of time. Computing power definitely comes into play here. For reference, I'm using my personal laptop with an Intel Core i7 1065G7 CPU 1.3 GHz with 12 GB RAM and an NVIDIA GeForce MX330 graphics card. As far as I'm concerned, I have a pretty average computer. It takes me about 12-15 hours to completely process a collection of 400-500 images in Metashape. When I imported my point clouds into CloudCompare it took a while to get the comparison finished because my CPU and memory were maxed out constantly. Performance was sluggish! I'm sure I can improve that as we fine-tune a workflow and find a good balance between quality and performance.

So, I'd definitely appreciate any help. I'm new to CloudCompare and I really hope it offers the solution we're looking for. I'll keep reading through the user guide and Googling away to see what I can come up with, but I thought it would be worth my while to see what kind of knowledge I could tap here. Thanks!

[daniel]

Hi,

Maybe a snapshot would help?

When you say 'delineate', would the scissors tool help? (https://www.cloudcompare.org/doc/wiki/i ... ation_Tool)

And regarding performances, is the overlap between the DEM and the point cloud(s) 100%? Otherwise you may want to set a 'max distance' to avoid CC to spend too much time looking for the nearest neighbors for nothing (i.e. for distances that are way too big, and you don't need to know them accurately).

[redleg_64]

Okay, here's a snapshot of what I'm working with. I want to measure shoreline recession, and I have an older data set (reference) and then a newer one to compare against the reference. It is difficult to determine the extent of the shoreline by examining the point cloud. I tried to use a series of polylines to mark the shoreline, but I wasn't able to create anything accurate enough to be meaningful. Maybe I'll just create them in QGIS and import them?

I've included screenshots of the compared point cloud and the profiles I extracted from it. I was thinking I might be able to use the profiles from each cloud, but I haven't got that figured out. Nevermind those holes...the ground was snowy in places.

I found a promising workflow that another team did. They used polylines to create an outline of the old and new shorelines. Then they established two perpendicular baselines (landward and seaward) and then placed transects across it at regular intervals. They they then used some buffers and other processes to calculate the distances of the shore to the transects. They call it the End Point Rate Tool for QGIS (EPR4Q) tool. It is a free and relatively simple tool that offers similar functionality to other complicated and costly software.

Do you have any ideas how I would be able to create a similar workflow with Cloud Compare? Is using point clouds even the right idea for the task at hand? Thanks.

[daniel]

CloudCompare is not particularly strong with polylines. Therefore if QGIS can already do what you are looking for, I believe it's the best path forward? (especially since I heard the latest version should now support 3D point clouds?)