Followup question--can markers throw off my alignment?

[bevenro]

Hi--I posted earlier today about an irregular UAV survey.  But until today I haven't had any problems with photo alignment--generally there's good overlap in specific areas.  When I run the align photos stage, usually I'll get about 90-95% alignment.

Today something changed, and I"m getting 0-5% of the photos aligned.  The only thing that is different is that I have added some guided markers, and added geographic reference info (lat/long/elev).  But now when I run the align photos stage, it doesn't work anymore.  I did check on some of the images, and a lot of the folded gray-flag markers are clumped together in individual pictures, so obviously I've done something wrong here.  Any idea where I've screwed up?

THanks!

[jwoods]

If you add markers before alignment the software will usually make it a priority to line them up according to the accuracy you've set for them. If you want to use markers you don't have to align with those markers first.  You can align the photos first without them as you normally would, then add your markers with the coordinates and hit the "refresh" button on the reference pane tool bar (looks like two arrows in a circle).  This will calculate the error for the markers without changing the camera alignment so you can see just where the problem is. 

Where are you getting the data for the coordinates of the markers?  Are are coordinates your using and the coordinates in photoscan in the same coordinate system and datum? 

[bevenro]

Hi Jwoods--thanks for the reply.

Markers were obtained via DGPS to an error of about 2-5 cm, which is fine for my purposes.  They're in decimal degrees. I'll check and see if I've got the reference system set incorrectly in Photoscan--where would I do that?

Thanks!

[jwoods]

In the reference pane toolbar there is a cross hammer and wrench which is the reference settings button, there will be a drop down selection for coordinate systems at the top.

I'll go back and read your earlier post about the irregular UAV survey and see if there's anything else about the process that might make me think there's a problem.  Almost everything, including photoscan, defaults to lat/long and WGS 84 so I would think its unlikely to be a coordinate system or datum issue. 

[jwoods]

I just read your original post.  Your project is way larger than I imagined, much larger than my projects that I normally work on.  I see your issue now as to why you want to align with GCPs first in order to speed up processing.  Probably breaking this into chunks as needed might be a good method but unfortunately I have little experience with that.  Hopefully someone more knowledgeable can chime in.

[bevenro]

Thanks, jwoods--

Yeah, it's a sizeable project, and because of the nature of the acquisition it's a bit all-over-the-place.  SO I'm trying to get what I can out of it, and use that as a basis for a possible grant for a full-coverage, systematic (cleanly gridded) survey.  Definitely not straightforward process though! Some sections align perfectly, some are awful, some GCPs got stolen--the works

Ultimately what I'll probably do is take about a tenth of the whole thing, somewhere with good coverage, get the best results I can, then use that small section to see what we can accomplish over the full area with a systematic approach.