Photo Alignment (Ortho)

[FrostBite]

     Could anyone PLEASE give me some work arounds for cameras that aren't aligning?? I have been doing a few Ortho Maps and theres always about 3 that aren't aligned.

I tried resetting camera positioning on the Workplace pane and I tried re-aligning from the Workflow menu with a lower accuracy setting but it doesnt do anything.

Does anyone have some tips??
Any help would be appreciate!!!

[HMArnold]

Assuming your images are clear, the basic problem we all learn for ortho alignment is image overlap.

If you look under the File pull down menu you will find a function to generate a PDF report

If you look in there you will see overlap values that I have never been able to understand.

If you post themore  here, Alexey will very politely tell you the images don't overlap enough.

He probably has a copy/paste library of about 20 ways to say that in perfect, polite English. I personally have received 4 or 5 versions.

Once you get your overlaps under control using grid width and platform speed, everything seems to start magically aligning.

Lat/Lon through an import file or image EXIF also helps a lot.

If you also include the platform heading  (yaw), and altitude, Photoscan does better with images taken during the turns.

The hardest ortho seems to be bare agricultural fields - everything looks the same, any picture can be pretty much substituted in almost any location. But with proper grid width, platform speed to give vertical overlap, GPS, altitude and yaw, Photoscan will lock down every image pretty much every time.

If you would like a downloadable test set to make sure you have everything set up right, let me know.

[FrostBite]

  I could try the downloadable test set. You would have to instruct me on how to set it up.

I am trying to do forests with an Inspire1. It has the Lats and Longs in each picture. As for the Yaw, grid width (overlap?) and platform speed. I'm not really sure how to set that and input it into Photoscan.

Have you done forest yet as an ortho? What is the MINIMUM Height above takeoff level that I should fly? Minimum overlap??? I've been trying a few different things. But also maybe Im not going through the workflow properly. Any help is appreciated!!

[HMArnold]

Here is a download link to a 150 acre set of images that's as close as we get here in South Texas to a forest. Some trees, lots of bushes.

https://spinnakersys.brickftp.com/f/eed7dea1c

Here is a link to download the resulting 21 megabyte orthophoto. Even at 21 megabytes it is greatly reduced.

https://spinnakersys.brickftp.com/f/48368b8f0

The mission was flown with a DJI Phantom 3 Pro at just under 500 feet using the Ultimate Flight app for Android.  Ultimate Flight also works on Inspire platforms.

The image set is comprised of 219 images, and will align properly in Photoscan using the settings and procedures outlined in the Photoscan tutorial "PS_1.1 - Tutorial (BL) Orthophoto, EM (without GCP).pdf". In my experience, any time you deviate much from the parameters in that tutorial other than High/Medium type choices for density, you're asking for trouble.

I'm attaching a KML of the mission

Set this up and run it, if you have any trouble, let me know.

You should be able to estimate the grid width from the mission KML, I show it to be right at 185 meters between legs. With a mission speed of about 18mph, there was sufficient vertical overlap to have complete alignment.

If you fly lower you will need the grid legs to be closer together and you will need to set the mission speed slower to get the same vertical overlap.

In answer to your question about the minimum possible height, I have never done any kind of analysis on that. The lowest altitude I fly at is 30 meters, but I assume you could fly lower than that if you wanted and still get image alignment if your grid width was very small and your speed was very slow.

Let me know if you have any problems aligning this set

Hank
Texas