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Technical “all Models Are Wrong, But Some Are Useful.”

Discussion in 'Anything Airgun Related' started by GPConway, Dec 22, 2019.

  1. GPConway

    GPConway Engaging Member

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    "So the question you need to ask is not 'Is the model true?' (it never is) but 'Is the model good enough for this particular application?" - George Box and others.

    Here's hoping ...

    I’ve recently developed a uniform scheme for a bunch of Android apps and have adopted it throughout - retrofitting as necessary - in advance of possibly popping them on the Google Play store. There’s no way that I’ll be paying Page & Brin's exorbitant entry fee but rumour has it that my wife’s already shelled out as a Yuletide gift ... If it transpires that is the case then the apps’ll still be free to download & use and definitely won’t carry any advertising distractions.

    All of the apps can be downloaded (for side-loading) from my webspace here

    KECalc:
    In response to a surprising number of arithmophobic/dyscalculic comments, the ‘formula-in-use’ can be replaced - by tapping on the item - with a simple set of instructions pertaining to the KE calculation inputs and units. Understanding that not everyone wants/needs/cares to know about the downrange dynamics, references to the settings and table have been relegated to the app’s option menu.
    In all other aspects, the app’s functionality remains unchanged.

    KECalc_Images.png

    MaxRange:
    Given the Muzzle Velocity, Ballistic Coefficient and applicable Drag Law, this app calculates the Maximum Range and Maximum Height of the projectile's trajectory at various inclination angles. Graphs and tables are provided to convey the calculated data.

    MaxRange_images.png

    PCPFills:
    As the name suggests, this app calculates the number of complete fills that are available from a pressure vessel of known size given the pressure and volume restraints and requirements. A table of Standard Scuba Tank Capacities is included in the action menu together with a list of popular PCP rifle reservoir volumes. The Compressibility Index for dry air is implemented at a nominal 20°C for the sake of completeness - although the practical measurable differences are surprisingly small - but for the sake of another dozen lines of Java, I'd rather make the answers nearer to correct than not.
    An additional efficiency section has been implemented which, given the number of shots/fill, the average KE of each shot and reservoir-related data already entered into the Fills section, allows the overall system efficiency to be calculated. Not something most folks would use every day but useful if you’re tuning or comparing PCPs or maybe thinking about an alternative/additional pressure vessel.

    PCPFills_Images.png

    EasyBC:
    This is a straightforward application which facilitates the calculation of a Ballistic Coefficient value using either one or two chronographs. The two-chronograph (∆V) method is preferred although it’s appreciated that few users have access to two matched and calibrated chronographs. The more demanding (and generally less accurate) one-chrono ∆POI method can give good results if a modicum of gumption is applied. The main problem with the ∆POI method is that there are many more things to get right and consequently many more interesting ways to get it wrong. A context-aware ‘Confidence’ page is also provided that calculates the extent of the errors to be expected both above and below the naïve value (i.e., that value calculated from measured/guessed/assumed inputs).
    The app also includes a basic analysis section giving details/graph/table derived from the calculated naïve BC value.
    Again, maybe not something you’d use every day but useful when required or if using ballistic applications like MERO, ChairGun, X-Act, Trajic (below) and several of the other apps introduced in this post.

    EasyBC_Images.png

    MAGCalc:
    This is an application to determine the accuracy of the magnification markings on scopes having a mil-dot, regular MoA or 30/30 reticle on the Second Focal Plane. It's often found that inaccuracies in the zoom ring's setting - where the real magnification can be considerably different to the marked value - are a leading cause of perceived accuracy problems with ballistics software. There are five interrelated variables here but the user has no control over the Calibration Magnification (as it is set by the design of the scope/reticle) or the dots/ticks/percentage spanned which are observed values. Much like the KECalc app above, the remaining three variables are interrelated such that the value of any one is calculated automatically from the values set in the remaining two - depending on which parameter is required.
    I’ve used the Mac version of this for a while checking my various Mil-dot scopes but this Android version also copes with regularly spaced MoA and the good old 30/30 as well.
    An extended Windoze/MacOS/Linux version of MAGCalc will be available in due course.

    MAGCalc_Images.png

    Validate:
    An app to validate the parameters of a trajectory via the POI at a chosen target range. Given four of the (measured) Muzzle Velocity, Ballistic Coefficient, Zero Range, Sight Height and ambient temperature/pressure, take a guess at the unknown parameter and the app will calculate a corrected value from a down-range PoI measurement. This is the Android version of the Windoze/MacOS/Linux app of the same name available from my web domain.

    Validate_images.png

    WindCalc:
    A calculator to estimate wind-drift at range given the muzzle velocity, Ballistic Coefficient and drag law of the projectile together with the absolute wind speed and direction relative to the direction of the target. The start of the wind effect can be offset (which is useful if shooting from a sheltered position). Similarly, the end of the wind-affected range can be specified - useful if shooting into a sheltered area.
    Either, neither or both of these offsets can be used as the scenario dictates.

    WinndCalc_images.png

    Trajic:
    Trajic is a trajectory calculator application. Using the same point-mass algorithms as MERO, it has facility for reticles with linear aim-point spacing: Mil-dot, Half Mil-dot, MoA and 30/30. This range could be expanded in the future although I’m not really aiming at a Chairgun clone/replacement.
    The app doesn’t included a BC-calculator page since this task can be handled by EasyBC but a modified version of Chairgun’s ‘good starting point’ pellet list is included on the basis that few users will bother to conduct their own BC tests anyway ...
    The app includes tables, graphs, projectile/user-file management facilities, utility functions and a fairly spectacular ‘heads-up’ inclinometer the intercept ranges of which get updated in near real time.
    Most views have access to an ‘options’ page - via the view’s action menu - to modify the currently displayed content so the app is very adaptable.
    I find Trajic to be intuitive in use so I haven’t included a helpfile; but then I know what’s required and what’s being done about it.
    If you need any help - or think that a helpfile is necessary - then please give me a shout and I’ll see what can be done for V1.0.2.
    Trouble is, help files are a PITA to write and apparently go mostly unread ...

    Trajic_Images.png

    Two things of which to be aware WRT Trajic:

    1) You’ll be asked for permission to access your device’s file-system.

    access_files_permission.png

    Permission can be denied (if you so wish) and the app will work just fine. However, all of the app’s files will be stored in the app’s sandbox so, if the (non-signed) app is updated at a later time, you’ll be starting again from scratch with all of your user-files, projectile database alterations, etc. gone for ever. Conversely, if permission is granted, the files will be stored in the external files directory (meaning external to the app’s sandbox) and won’t be adversely affected until you choose to delete them. They’ll also be available to transfer between Android devices ...
    Despite the warning notice above: this app doesn’t access your photos or media and it accesses only those files that it created on installation and those subsequently created by the user.

    2) You’ll be asked to give permission to use the device’s camera.

    access_camera_permission.png

    This permission is used only to display the camera’s preview surface as the inclinometer view’s background. Trajic will neither take pictures nor record video but such is the granulation of Google’s permission system where everything get lumped into the same control. However, if the permission’s not granted, Android’ll prevent the inclinometer from working. Simple as that. Not my fault.

    I don’t own an Android mobile but all of the above have been developed and tested on a wide range of Android Studio emulators and ultimately installed and tested on my wife’s el cheapo Huawei P9 lite device that is currently stuck on Android 7.0. In testing, all of the apps have been successfully side-loaded from my web-space, so I at least know the download/side-load bit works as intended.
    The emulators run the all of apps well enough with all Android versions from Android 16 (KitKat, API 4.1) and beyond but performance on real devices might be variable. If you have problems then please let me know and I’ll see what can be done.

    As ever, constructive criticism of any of the above apps is welcome. Encouraged even.
    Hysterical rhetoric and infantile ‘banter’ not so much.

    George
     
    Last edited: Dec 22, 2019
    Tim_B, rabbitwrecker, Shoto1 and 20 others like this.
  2. Figgy

    Figgy Posting Addict

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    Looks good, much like chairgun.
    I've been using strelock pro but when you release your app I'll give it a try. Some good features not found in other apps.
     
    Last edited: Dec 22, 2019
    windymiller likes this.
  3. Gary Jones

    Gary Jones Very Active

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    Wow mate. Looks great. You e obviously invested a lot of time into it. :claping::claping::claping:
     
    windymiller likes this.
  4. terry1001

    terry1001 Major Poster

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    George, that's a terrific bit of work - well done! :up::up::up::up::up:
     
  5. Jim Beam

    Jim Beam Engaging Member

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    Well done, this looks brilliant
     
  6. genesis

    genesis Busy Member

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    Looks spot on ,.:up:
     
  7. myiot

    myiot Engaging Member

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    Looks great to me! :) The most important thing is how easy it is to use.
    Make sure to test it with a few technically 'challenged' folk.
     
  8. Steved

    Steved Engaging Member

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    I was unable to understand any of that after the first three words.
     
  9. jesim1

    jesim1 Kit bitch to the Stars

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    I get it, but it's a struggle to get through it all - perhaps an idiots guide for the bullet points would be good for those of us with a short attention span/

    Overall this sounds excellent, it's too much for me or the average plinker, but I can see great uses for it with those at a higher level, particularly if you go FAC and need 100 yard distances in real life.

    Well done mate :thumb:

    James
     
    Tim_B likes this.
  10. secretagentmole

    secretagentmole Low down, dirty and quiet...

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    That looks great. Will be downloading these.
     
  11. GPConway

    GPConway Engaging Member

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    Thanks.
    A few of the basic algorithms were provided by Chairgun's author - HarrysLad - but I've taken the opportunity to speed them up, revise and refine them a little (that's what I do). The GA Drag Law is HL's (now probably Deben's) but the others are already in the public domain. The BC lists are from Chairgun too although I've taken the opportunity to couple individual projectiles to their appropriate Drag Laws. 'Under the bonnet', all of the apps have something to owe to Chairgun/HL/Deben, but these particular apps are stand-alone rather than bungled into one bulky package. Chairgun is far more comprehensive anyway.
    The apps are available from my web domain for side-loading but, depending on the generosity of my wife (and the strength of the rumours of a Yuletide gift), they may never be available from Google Play.

    Thanks. That's what boredom and a six-week stay in hospital will do for you!

    Thank you gentlemen. Appreciated.

    'It'? There are eight stand-alone applications listed. To which do you refer?

    Right. So maybe English isn't your first language. Give me a clue and I'll put Google Translate on the case. Or maybe you could.

    The apps all have an Information panel on the first page after the splash screen but it's usually concerned with what the app's for rather than the specifics of how to use it.
    I'll try to improve that situation - maybe via access to a web-page or similar.

    Average plinker? Probably not.
    The apps certainly aren't limited to 100 Yards range or to airgun projectiles or velocities. The guy who owns the adjacent finca has used the EasyBC, MAGCalc, WindCalc and Trajic apps to great effect with his 0.223 Remington and 0.17HMR as have I with my 0.177/0.22 AA S410's and (FAC in UK, legal in Spain) 0.22 HW80 in testing and proving.
    Pretty useful for long-range plinking and Pellet testing though.

    George

    [Edited for spelling. Doh.]
     
    Last edited: Dec 23, 2019
    SlugFest and pbrown like this.
  12. secretagentmole

    secretagentmole Low down, dirty and quiet...

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    @GPConway Why not show them off to Hawke? See if they take them up...
     
  13. Figgy

    Figgy Posting Addict

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    Mole Hawke have stated they're not interested in maintaining the app or data in chairgun.
     
  14. Pete236

    Pete236 Big Poster

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    That all looks superb to me.
    I'm not technically minded at all, tech is a closed and chained shut book to me!
    But from what I've been able to understand (and it's my lack of knowledge that's let me down!) the apps all seem to be what I've been looking for for ages!
     
  15. GPConway

    GPConway Engaging Member

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    I nearly forgot ... there's one other app on the Android page of my web-space.

    ClickCalc:
    ClickCalc is a calibration app arranged to accurately determine a scope's 'Clicks per Minute-of-Arc' characteristic. As with most manufactured items, this may not be as stated by the manufacturer and may lead to errors both in the field and when used with ballistics software.
    Like KECalc and MAGCalc above, this app simply manipulates three parameters to calculate an unknown fourth. In most scenarios, the unknown value would be the ‘Click/MoA’ value as per the first image below (a Hawke scope with a claimed 4.0 Click/MoA characteristic).
    Once the Clicks/MoA characteristic's been established (or even if you're using the manufacturer's value), scrolling the page upwards displays a quick-zero map where the corrective elevation and windage click values are displayed for the selected range and C/MoA value.

    ClickCalc_images.png

    Like the other apps aforementioned, this may/may not be available on the Google Play site. At least for now, it's available from: here

    George
     
    Last edited: Dec 22, 2019
    Dr B and pbrown like this.
  16. John Entwistle

    John Entwistle Busy Member

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    Looks very good and definitely worth sideloading sadly I don’t use Andriod systems anymore
     
  17. secretagentmole

    secretagentmole Low down, dirty and quiet...

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    It might be worth pointing out to Hawke...

    'This ain't bloody Chairgun!'
     
  18. Figgy

    Figgy Posting Addict

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    So why would Hawke be interested?
     
  19. GPConway

    GPConway Engaging Member

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    Interesting. I find myself swimming off in the opposite direction with regard to mobile phones. I've bought Apple hardware for years but they do seem to have lost their way of late. (The $999 monitor stand? Seriously? :rolleyes:) Nothing wrong with iPhone quality but I don't think I'll buy another one when my current iPhone 6s is no longer supported - too many silly 'features' added that nobody requested or needs and will only be used by the most ardent Apple fanboy. Additionally, a basic iPhone 11 is now so expensive that you have to think that they're just extracting the urine. My next mobile will be a cheap, virtually disposable, (non-Samsung) Android device.
    There, I've said it now so it must be true. :)

    That's not going to happen. Chairgun and X-ACT, while retaining the excellent basic ballistics functionality, eventually became a catalogue of Hawke scopes. Fair enough, I guess Deben wanted a marketing tool to supplement/enhance their products and web presence, and they got what they paid for. The continuing support and maintenance problems of the software products over four diverse (buggy and variable operating systems: iOS, Android, OSX and Windoze) platforms must have been horrific though. I couldn't do that and I won't ever be drawn into a similar situation (again :facepalm:).
    Anywayup, I write software these days for the joy/interest/utility of it, not for profit, so what'd be in it for me?
    The apps currently contain no explicit Deben content (and for the reasons outlined above, I'm unwilling to add any) so what'd be in it for them?

    George
     
  20. John Entwistle

    John Entwistle Busy Member

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    Sadly I went the other way, in the past I did techie type stuff for Virgin Mobile (when they won all the awards for 9 or so years on the bounce) and it was Android Software I supported but a few years ago when I retired my wife bought me a 7plus to go with my long serving IPad. No idea what will happen in the future, but I’m not paying a grand for a phone unless it’s Monopoly money
     
    GPConway likes this.

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