Processing images that are mostly grass


#1

Does anyone have advice to improve processing images of grassy fields. Webodm recommends changing some setting minimum number of points and enabling pvms. I have tried this but it has not solved the issue.

I am taking images of a grassy field from a height of about 5m using a MAPIR survey3 rgb with attached gps. This is not a standard drone practice so it might contributing to the issue. The gps positions are good but the images are stitching into one block. I am not using gcp’s but plan to try using them.


#2

Hi @Thomas_Eley – can you give more info on the problems you are having?


#3

I am having trouble post-processing images of a grassy field. The gps points look ok in geosetter but when I try to process the images in webodm it does not work. This is probably due to a lack of gcp’s, or other identifiable points, but if anyone has suggestions about improving post-processing of relatively homogeneous areas of ground it would be appreciated.

I end up with either a single square at the start of the survey or a single square at the end. Ideally I would like images locations to closely relate to the exif data and then be adjusted to fit the next images. What currently happens is one square visible either at the beginning or end of the line I have photographed.

I am doing something that is not standard eg photography from a 5m pole rather than a drone 20m+ high. I have not used gcp’s yet. Any advice regarding post-processing options would be helpful.


#4

What is your overlap and sidelap, or are you doing your pictures in a single line?


#5

I am just doing a single line at present. I am trying a technique mapping using a pole camera so it is at an experimental stage. I am working on improving my field technique but what I also need to do is improve my post processing.


#6

A single line is unlikely to work with ODM. I would recommend 3 lines if you can afford it, and two lines at an absolute minimum.


#7

Thanks. I will try it. I have managed to process a single line by placing gcp’s every 4-5m. They are just coloured bean bags with numbers written on them but they seem to have worked.

The next problem I can foresee is that if I process 2 or 3 lines at the resolution I want then my laptop is likely to struggle. I am going to upgrade from 8 gb to 16 gb of ram but is there a way to reduce the file size of the orthophotos when adding them to QGIS?


#8

Hi @Thomas_Eley – check out --orthophoto-resolution here: http://docs.opendronemap.org/using.html#additional-arguments

It’s pixels per meter rather than meters per pixel, so 20 (which is the default) is 0.05 meter pixels.