what exactly would you like to measure, e.g. percentage of gaps per line?
In general you need two steps: 1) segment your trees and b) detect your plantation lines.
For segmentation of the trees I tried converting to HSB-stack, slight morphological closing (MorphoLibJ needed) and then thresholding:
run("Duplicate...", "title=Brightness duplicate range=3-3");
run("Morphological Filters", "operation=Closing element=Square radius=2");
I then searched for a solution to automatically identify the individual plantation lines. I automatically determined the median distance between lines (in this image around 38 pixels) and then was thinking to shift a user-drawn poly-line by this value. This does not work well because of non-regular distances between and unregular shape of the plantation lines in the image.
So for now I can only think of rather ugly manual approaches:
To get the percentage of gaps:
1. Manually draw a poly-line along one plantation of linewidth 1 in the binary image.
2. Measure Integrated Density and Area. Ratio of gap/plantation line is: Integrated Density/Area*255
To count the number of non-gaps:
1. Manually draw a poly-line along one plantation of linewidth 25 in the binary image.
run("Line to Area");
run("Analyze Particles...", "size=5-Infinity summarize add");