I am hoping to view sky luminance values from CIE and weather based skies. I can generate the HB false color image but would like luminance values not W/sr-m2.
The legend unit input is not accepting “cd/m2”.
What is the best method to convert these units? or am I missing something in how to create these luminance sky maps?
I can add “179” to the conversion input. is that just assuming a lumens/w luminous efficacy conversion of 179? where does that number come from? Somewhat related, this still does not change the legend title.
The issue is not so much with the False Color component but, rather, it’s that the Visualize Sky component is currently only set up to render the sky in the full solar spectrum. Changing it to just be for the visible part of the spectrum requires a little more than just multiplying by the 179 conversion factor.
I forget what parameter of the sky needs to be changed to make sure that it is in the visible part of the spectrum but I’ll post back here if I get to check it.
Actually, what I said earlier is only really relevant for climate based skies. I forgot that CIE skies are always defined in the visible part of the spectrum. So you’re right that the only thing you really need to do is multiply by 179 if you’re using CIE. If you want to get a luminance view of a CIE sky, you can use the following workaround with the HB Check Scene component:
That makes sense. Thank you @chris for sharing the above and explanation, worked for me but I have two follow up questions:
I tried playing with the up vector but it seems the sky is mirrored. below is a snip of 9am but the sun is on the western side (assuming north is up and I am looking at sky dome from above).
is it possible to click and get the luminance value based on the image? I tried referring to the Radiance values but I’m seeing values on the order of 100x less than expected.
You are watching the sky dome from below. So what you are seeing is correct, although perhaps counterintuitive; left is west, and right is east.
You cannot get the values from the false color image since it is no longer an HDR image. You can add the HDR image to the ImageViewer and use the same coordinates for both images. Remember to account for the legend width. visualize_sky_luminance_coordinates.gh (40.2 KB)
Understood on item 1 - is there a way to flip or mirror the vector or image so that it is more intuitive ie, more like the sunpath preview or sky radiation maps? Worst case, I suppose I could flip it in photoshop post-process.
I tried a similar workflow for gathering info from the .hdr file not the false color image. I’m getting a color RGB value not a luminance value - am I perhaps missing a radiance component?
simplified script is below. visualize_luminance_sky_RS.gh (33.1 KB)
Anything is possible with Radiance. You can use pflip either horizontally or vertically. In the custom Python script, I used the horizontal option. visualize_sky_luminance_coordinates_mirrored.gh (43.6 KB)
For the other question, right-click on the ImageViewer and make sure “Get Radiance Values …” is selected.
wow, thank you. Python script did the trick
I had to click on the white image first to get it going, clear values, then with “get Radiance values” selected, I started to get the luminance values when using the XYZ constructed point.
