calc_zenith_colrow: Calculate zenith raster coordinates

In rcaiman: CAnopy IMage ANalysis

Calculate zenith raster coordinates

Description

Calculate zenith raster coordinates from points digitized with the open-source software package ‘ImageJ’.

Usage

calc_zenith_colrow(path_to_csv)

Arguments

path_to_csv

character vector of length one. Path to CSV file created with the ImageJ point selection tool.

Details

In this context, “zenith” denotes the location in the image that corresponds to the projection of the vertical direction when the optical axis is aligned vertically.

The technique described under the headline ‘Optical center characterization’ of the user manual of the software Can-Eye can be used to acquire the data for determining the zenith coordinates. This technique was used by \insertCitePekin2009;textualrcaiman, among others. Briefly, it consists in drilling a small hole in the cap of the fisheye lens (away from the center), and taking about ten photographs without removing the cap. The cap must be rotated about 30º before taking each photograph.

The point selection tool of ‘ImageJ’ software should be used to manually digitize the white dots and create a CSV file to feed this function. After digitizing the points on the image, use the dropdown menu Analyze>Measure to open the Results window. To obtain the CSV file, use File>Save As...

Another method (only valid when enough of the circle perimeter is depicted in the image) is taking a very bright picture (e.g., of a white-painted corner of a room) with the lens uncovered (do not use any mount). Then, digitize points over the circle perimeter. This was the method used for producing the example file (see Examples). It is worth noting that the perimeter of the circle depicted in a circular hemispherical photograph is not necessarily the horizon.

Value

Numeric vector of length two. Raster coordinates of the zenith. These coordinates follow image (raster) convention: the origin is in the upper-left, and the vertical axis increases downward, like a spreadsheet. This contrasts with Cartesian coordinates, where the vertical axis increases upward.

Note

This function assumes that all data points belong to the same circle, meaning that it does not support multiple holes when the Can-Eye procedure of drilling the lens cap is applied. The circle is fitted using the method presented by \insertCiteKasa1976;textualrcaiman.

References

\insertAllCited

Examples

## Not run: 
path <- system.file("external/points_over_perimeter.csv",
                    package = "rcaiman")
calc_zenith_colrow(path)

## End(Not run)

rcaiman documentation built on Sept. 9, 2025, 5:42 p.m.