[GRASS-user] Orthorectification of tilted digital camera images

[Blumentrath, Stefan]

Hi Markus, Florian, and others,

Thanks for your replies. I still did not solve this, so I am grateful for any hint.

Now, I extracted the relevant data (XY-location containing the mapset (“reconyx”) with the image group (containing i.ortho.photo files), and camera file as well as the target location (“ETRS_32N”) with the “target” mapset containing the DEM (“dem_1m”) and two of my attempts for orthorectification (with and without INIT file active).  You can fetch the zip-file with the GRASS DB (22 MB) within the next 30 days from:
https://www.dropbox.com/sh/swri19zn5m9gb7w/AACADlkqGZKO_JMS_YbLNXBXa?dl=0
There you will also find the original image (“IMG_0015.jpg”) as it comes from the camera.

As a next step I will take another test image with a more orthophoto-like perspective and no visible sky. I hope, that way I can check whether the issue is due to the chosen camera position / angle or the way I defined the exposure in the INIT file…

I have a strong feeling that my problems - in one or the other way - have to do with camera angles…

Unfortunately, it does not seem to be possible to specify only the exposure parameters one is sure about. i.photo.rectify uses either all or nothing to initialize the orthorectification algorithm…

Cheers
Stefan

From: grass-user-bounces at lists.osgeo.org [mailto:grass-user-bounces at lists.osgeo.org] On Behalf Of Florian Mueller
Sent: 15. august 2015 20:54
To: grass-user grass-user (grass-user at lists.osgeo.org)
Subject: Re: [GRASS-user] Orthorectification of tilted digital camera images

Dear Stefan,

Can you provide some example photos in a Dropbox (e.g.) folder?

Best regards,
Florian


On Sat, Aug 15, 2015 at 7:53 PM, Markus Neteler <neteler at osgeo.org<mailto:neteler at osgeo.org>> wrote:
On Tue, Aug 11, 2015 at 11:37 PM, Blumentrath, Stefan
<Stefan.Blumentrath at nina.no<mailto:Stefan.Blumentrath at nina.no>> wrote:
> Dear all,
>
> Although there is a lot of relevant information regarding the
> orthorectification of tilted digital camera images in GRASS GIS online
> (here:
...
> Does up-slope direction of the photo or sky in the photo conflict with the
> orthorectification algorithm?

I have no idea... in general the algorithm is very robust but was
really written for aerial photos.

>
> When it comes to the GCPs I am in principle quite confident that they are
> placed OK. Or do you think that GCPs measured by a hand held GPS are too
> imprecise?

They should be fine.

> However, depending on initial camera settings RMS something like 268, which
> indicates that something is wrong here. If I do not use i.photo.init, the
> image is placed much better (RMS around 10-20), but still pretty poor…

About 10 years have passed that I tried the last time, memory is fading...

Did you figure it out?

...
> Btw: Some of the submodules of i.ortho.photo are not linked to the /bin
> folder in GRASS 6.4.5svn, so I have to start them like this:
> /usr/local/grass-6.4.5svn/etc/i.photo.init

To my knowledge they are intentionally hidden in order to be run from
the i.ortho.photo main menu (in GRASS GIS 6).

Markus
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