Comparing two DSM:s

[KR W]

I did a capture of a land fill area a couple of days ago. The area is going to be filled with excavation material, and the owner would like me to do EXACTLY the same capture in six weeks as I did two days ago. He would like to hade the DIFFERENCE between these two DSM expressed as a new DSM.
Is this possible?
I'm using ALTIZURE to create 3D:s, Otrhomosaics and DSM:s, and I mailed to their support with my question. Their rather short reply to my support question was

"We do not provide software to analyze DSM file, we are producer of DSM file.There are other software can do the analysis work on DSM, for example to compare two DSM file."

but I didn't get any hints on where to find them, and as always they are rarely answering follow up questions. Dead silence...
I have been searching the whole morning without success. Can any of you skilled guys help me? Are ther such services/software, and where are they?

Best regards

Roger

 

[Richard R]

What you want to do is known as "change detection" and it's a tough nut to crack. Not the least of the problems is just registering the two maps. With pixel sizes several times smaller than position errors, making sure that you are actually comparing the same pixels is very difficult. Check out this page on doing so with qgis Change Detection in GIS ~ GIS Lounge
This is an amazing program that you can download and run on about any PC or laptop.

 

[KR W]

What you want to do is known as "change detection" and it's a tough nut to crack. Not the least of the problems is just registering the two maps. With pixel sizes several times smaller than position errors, making sure that you are actually comparing the same pixels is very difficult. Check out this page on doing so with qgis Change Detection in GIS ~ GIS Lounge
This is an amazing program that you can download and run on about any PC or laptop.

I totally agree with you on QGIS. It's like Excel. You'll never reach the bottom. There is always something new to learn..
I'm using QGIS (and SAGA GIS) to set max and min values in my DSM:s. I didn't know that "change detection" was possible to do. Unfortunately I'll have to wait some six week before I can lay my hands on a second version of the DSM..

Thanks for your help!

 

[Richard R]

Why wait, can you fly another mission over the same area now? That would give you material to practice with until you take the money shot. Let me know how it works out for you.

 

[KR W]

Because It's so expensive to get the new DSM. And I haven't got neither the software nor the hardware to do it at home.
I guess I cold use the same DSM as the first one, of course. For the training...

 

[Richard R]

Don't know which bird and tablet you are using, but you might want to look into Map Pilot by Maps Made Easy Drones Made Easy Map Pilot App for iOS
You can fly use MP to plan and fly photo capture missions then upload the images to MME for processing. For small missions (usually around 100 photos), they will process them for free! Larger missions can be processed on a pay as you go basist that is pretty reasonable. The outputs are orthos, 3Ds and DSMs. Yes, you have to buy the MP app, but the last time I looked it was still only $20.
I thought of something else as I was writing this. Your GPS altitude error will likely be different in maps taken on different days, possibly even on maps taken on the same day! Before processing for change, you may have to register or 'normalize' the MSL altitude of the maps. Don't know offhand, but wouldn't be surprised if qgis could do that too.

 

[doktorinjh]

Is this possible?

There are several applications that can do this and we've been successful comparing point clouds and DEMs. You should look at Cloud Compare and Global Mapper. Your best results will be using the same ground control targets for both missions, so lay some out where they won't get disturbed. We've been able to measure minute changes (less than 0.25' in the vertical) and have validated the changes in the field.