How to scale orthophotos without GCP's?

[Napo]

Hi everybody,

I need to make some measures from an orthophoto, but I only have terrain distances measured at the field, no GCP's.

Can anyone please help me??

Thanks in advance,
Napoleon

[stihl]

If you have measured dimensions of objects that are visible on the ortho, you can use two scalebars to scale the ortho.

If you open one of the photos in photoscan which has said object in it place a marker on its, then mark both markers in as many photos as possible.
Then in the marker pane to the left select both markers and right click and select "Create scale bar".
A new scalebar will appear in the pane below it. Then double click on the distance and enter the defined distance.

It's best two make two scale bars perpendicular to eachother so you get the X and Y axis correct.

[Napo]

Thanks so much, I will try to do it following your advice!