Where to stand when measuring sunlight?

A user asked the following:

“I really like the app. So easy to use! 
“My latest use case is that I have 2 rows of 4 raised garden beds and the perimeter area is surrounded by trees. I want a reading for each bed. Where should I stand? Consistently at the head or foot of each bed? In the center of the bed (difficult as I currently have crops in them)? In the general vicinity of the 8 bed footprint ( 30×25 feet)?
“I’m taking readings for this area as well as each area I plan to grow in. I never know where to stand.”

Y.B.

As far as your use case, here’s the story.   SASHA measures the direct sunlight at the location of the camera.  If you stand at the end of a row, it will be measuring the sunlight at the end of the row at the elevation you are holding the camera.  Likewise at the middle of the row, etc.  Therefore, the most accurate measurement for the end of a row of radishes, for example, would be taken at the end of the row at the level (elevation) where the radish foliage will be.  Needless to say, it would be awkward to do that, although it is possible (e.g. lie down on the ground and take a measurement, or place a mirror on the ground to see the screen as you scan).   The only time I would recommend doing something like that would be when another low plant or obstruction is the cause of shade.   In most cases, where shade is caused by trees or buildings, standing at the location of interest, or a step or 2 South of the location, would be close enough.  You can use your own shadow a rough guide for how far away to stand.

Your growing plot is large enough that a “shade map” would be valuable.  A primitive shade map can made by subdividing your plot into squares (about a yard on a side) and taking a measurement for each each square.  Plot your readings on graph paper, or enter into a spreadsheet and create a “surface” plot.  It may not be practical to do right now, as you mention that your cops make it difficult to get into the middle of the beds.

Given that the crops are in the way and you can’t get into the middle of a bed, you might consider interpolation:  take a measurement at each end of the bed, and assume that the amount of light changes steadily (linearly) from one end to the other.   So if you have 4 hours on one end, and 8 hours on the other, you can assume that you have 6 hours in the middle of the bed.  This is an approximation, of course, but it might be better than nothing.  You can do the same thing across the beds….

Before you do all of this, make sure your device’s compass is behaving well.   The device compass is the largest source of inaccuracy in the app (due to the fact that the device itself creates electromagnetic field which can confuse its compass).  If you have a case with a magnet, take the phone out of its case. Do a google search for “Android compass calibration” and follow the instructions (usually some version of a figure 8).  A sure sign that the compass needs calibration is that the “tiles” (or “cells”) on your screen drift relative to the background scenery.   This drift means the compass has not “locked in” on North.

6 thoughts on “Where to stand when measuring sunlight?

  1. KK

    George, Is there any chance that you’ll do an iPhone version of this app? Would begging help?

    I’m going to try running it under emulation, because that’s how useful it would be for me. I’ve got a small urban plot and I do okay with ornamentals, but placing vegetables is kind of beyond me, and almost every other method for figuring this out has me exhausted.

    Also how does the app cope with fences?

    Reply
    1. gkoulomz Post author

      Sorry for the late reply. I kind of expected WordPress to tell me that I had comments, but it didn’t. I’ll have to look into that….
      As far as your question, iPhone implementation requires a complete re-write, so don’t hold your breath, please!
      Sasha should work fine with fences. If fence lets light through, Sasha sees the sun coming through, and counts that. If it doesn’t, Sasha doesn’t see the sun and doesn’t count it. However, if in foliage simulation mode, Sasha may interpret the fence as being solid. It’s not smart enough to distinguish a bunch of bare branches from, say, a chain link fence, and may estimate foliage onto the chain link fence.

      Reply
      1. KK

        Hi, hopefully you’l get this one too. Is there a way to find out what the system requirements are to run it, I’m considering picking up a used phone to run this. If I do will it work with wifi, if I don’t have it hooked up as a cell phone,?

        Reply
        1. gkoulomz Post author

          The formal requirement is an Android device with Camera, Magnetic, Gravitational, and Location sensors running at least API level 19. In practice, the age and capability of the device make a difference in terms of how quickly the app runs. The oldest device I have is a Samsung TAB3, and I find it painfully slow. I have a pixel 2 and 3a, which run reasonably well. My Pixel 3 is even better. My OnePlus 6T runs quite well.

          Except to send feedback via email, SASHA does NOT require internet or Voice; it is entirely self sufficient. You do not have to get a cellular plan, just the device. Of course, WiFi is helpful to install the app.

          Here is a list of devices to which users have downloaded SASHA, most common first:
          Nexus 5X
          A6013
          Pixel 3
          SM-G960U1
          Pixel 3a
          Pixel 5
          Redmi 6A
          SM-G960U
          SM-G965U
          Pixel 3 XL
          SM-N960U
          Moto Z2
          SM-G965F
          SM-N986U
          SM-G950U
          SM-G998U
          SM-G986U
          SM-G973U
          SM-N986U1
          E6910
          SM-G960F
          H932
          Moto E
          Moto E(4)
          Pixel 4a (5G)
          SM-N981U
          LM-G820V
          Moto G Power
          Pixel 4a
          Pixel XL
          SM-G981U
          SM-G981U1
          SM-T700
          VS986
          XT1789-05
          BAH2-W19
          E6820
          KB2007
          LM-V600
          LM-X220PM
          M2007J17G
          Mi MIX 3 5G
          Moto G7 Plus
          One 5G UW
          Pixel 2
          Pixel 4
          Pixel 4 XL
          SM-A217F
          SM-A516U1
          SM-G930V
          SM-G950F
          SM-G955U
          SM-G977U
          SM-J737V
          SM-N960U1
          SM-N975U
          SM-T210R
          XT1021
          H918
          Moto G7 Power
          SM-G970U
          SM-G970U1
          SM-G991U

          Reply

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