Update created models with changes

[obw]

Hi there.

We are using Agisoft for mapping purposes.

Is there any way to fly over an area again and only implement the changes to a already created model? Mining, Construction areas etc. Is there a quick way to to this, or do you have to create every model from scratch even after the initial first model?

-Ben

[SAV]

Hi obw,

If you only want to change a small area of the model and don't care about other areas (e.g., in the case of a mine, you might just want to update a new stockpile which is part of a much bigger model for the whole mine), the workflow outlined below might do the job:

Note: This workflow assumes that you already have a 3D photogrammetric model of your mine and only want to add an area where there is a new stockpile.

1. Start a new Photoscan project, import the pictures for the new stockpile (and some surrounding area) and process them to generate a dense point cloud (use the same coordinate system as your existing mine model)
2. Import dense point cloud of mine model using FILE>APPEND (you should have two chunks in one project now)
3. Place markers at the same locations in both models/dense point clouds (they need to have matching names/labels)
4. WORKFLOW > ALIGN CHUNKS > MARKER BASED
5. Cut a hole into the dense point cloud of the mine model by selecting and deleting points in the area of the new stockpile (SHOW ALIGNED CHUNKS which is the second button from the right in the upper toolbar might be helpful for this step because it will allow you to show the new stockpile model 'on top' of the mine model)
5. WORKFLOW > MERGE CHUNKS > MERGE DENSE CLOUDS
6. BUILD MESH/DEM/TEXTURE/ORTHOPHOTOGRAPH of the just merged chunk

I hope that's what you wanted to achieve.

Let me know if it worked for you.

Regards
SAV

[obw]

Hi SAV.

Thanks for your quick and detailed reply.

This is partly what we are looking for and is a great example when we know what part of the area that has changed. The trickier part is when we don't know where the changes are, or there are many changes (i.e a large Construction area) and we would like to scan this regulary. Is there any way to find the diffrences and only process them. Or kind of automate them?

The point would be to show the progress over a given time period, but if we have to create a model from scrach each time we have to reduce the intervalls between the scans.

-Ben

[SAV]

Hi Ben,

I fear that in your case you'll have to generate a new model for the whole area every time and then compare it to the previous model in order to accurately identify and assess changes. It would be quite incredible if PhotoScan knew what has changed before even processing your imagery. PhotoScan is a great piece of software, but cannot do magic 
However, PhotoScan allows you to automate/simplify your processing workflow (more details later).

To mitigate/solve some of your problems, I suggest to get more powerful hardware and/or to change processing settings. This should help to accelerate your workflow. For example, if your client just wants a DEM (+contour lines) and/or a orthophotograph, you can choose HEIGHT FIELD during processing which saves already a lot of processing time. Additionally, it might be sufficient to build the dense cloud at MEDIUM quality settings (e.g., many mines don't care about a few cm). Your models should be fit for purpose, that's all 

If you fly the same (UAV) survey over and over again to detect changes, you could definitely automate your workflow either by simple BATCH PROCESSING or more advanced PYTHON SCRIPTING. The latter gives you more flexibility. I would, for example, use 'fixed' ground control points that don't change and are used in every model. Makes it much easier to align/compare models later.
Depending on your project, PhotoScan's DETECT MARKER function might come in handy as well. You would need to adjust the size of your ground control points to your GSD though (details in other posts of this forum). Photoscan would then assist you in finding markers in all images, which can be time-consuming when done manually.

Regards
SAV