Author Topic: OS maps for my new phone???  (Read 2122 times)

vizzavona

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Re: OS maps for my new phone???
« Reply #45 on: 17:24:32, 08/09/20 »
Hello.... With the Memory Maps that I have on the phone it is possible to get a ten figure grid reference by pulling down a 'tab thing' from the top of the screen when using the maps.


Eyelet

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Re: OS maps for my new phone???
« Reply #46 on: 18:30:16, 10/09/20 »
The OSMaps app will also give you a ten digit Grid Reference, by pressing and holding the desired location.

ninthace

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Re: OS maps for my new phone???
« Reply #47 on: 19:14:40, 10/09/20 »
The OSMaps app will also give you a ten digit Grid Reference, by pressing and holding the desired location.
And it offers a share option which, if you email or Whatsapp, will send a hyperlink showing the location as a dropped pin on the OS  website.
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gunwharfman

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Re: OS maps for my new phone???
« Reply #48 on: 19:19:06, 10/09/20 »
Excuse my ignorance but why would I need an eight or a ten digit grid reference?

ninthace

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Re: OS maps for my new phone???
« Reply #49 on: 19:30:07, 10/09/20 »
Excuse my ignorance but why would I need an eight or a ten digit grid reference?
To specify a location more precisely.  For example, where a particular object is located or where a picture was taken.
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Eyelet

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Re: OS maps for my new phone???
« Reply #50 on: 20:45:10, 10/09/20 »
For the same reason we use 6 digit grid references rather than 4 digit grid references - the GR positions your location in a smaller area:


4 digit e.g. SK 54 16         1000 x 1000 m (1,000,000 sq metres)
6 digit e.g. SK 540 162       100 x 100 m (10,000 sq metres)
8 digit e.g. SK 5405 1623     10 x 10 m (100 sq metres)
10 digit e.g. SK 54058 16239  1 x 1 m (1 sq metre)

That said, with the current state of the art for consumer GPS devices we cannot get sufficient precision to locate ourselves to a single 1 x 1 m square and even to a single 10 x 10 m square is a challenge. The EU Galileo GNSS project however is aiming at sub-metric precision more akin to professional surveying GPS devices which use two signals from each satellite instead of one, so we may be able to do it on our phones in a few years.

 
« Last Edit: 21:29:28, 10/09/20 by Eyelet »

vizzavona

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Re: OS maps for my new phone???
« Reply #51 on: 08:17:15, 11/09/20 »
Thanks for that eyelet. O0
As well as the MM maps now on the phone transferred from my purchase that I made for the PC many years ago.  I also have the Ordnance Survey maps on the Annual fee. Up till know I got the map references via the OS Locate feature...6 figs.
However as you said the more accurate refs. are available when the map feature is 'pressed'.
Eight digits with the two alphas to locate...then additionally the ten digit location is preceded by another digit and East and North.  Does the East and North prior to the digits take the place of the two Alphas that we are familiar with to give a reference within the 100 Kl. 'square' of the system?
I'm sure that you will keep me right on this as you seem to be well up on all this.

fernman

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Re: OS maps for my new phone???
« Reply #52 on: 09:42:19, 11/09/20 »
That's an interesting point. A 6-digit GR will put you in a 100m x 100m square and an 8-digit GR will reduce that area to a 10m x 10m square which could be useful as you have indicated.

However you have to bear in mind that the app is getting its position fix from the GPS chip and converting it to a GR mathematically. Most phone GPS chips will give you an uncertainty in your horizontal position fix of say +/- 5m 95% of the time, giving your position in a 10m diameter circle. That 10m circle is most unlikely to just fit precisely inside a  single 10m x 10m square and considerably more likely to overlap with two, three or four adjacent 10m squares, so the point estimate of your 8-digit GR may not be quite as accurate as you think.[

I have used a Garmin eTrex H to check plant records (ferns, of course!) that have 8 figure grid references in woods and elsewhere, and every time it has been a case of go to the point, look around you and there it is within a few feet. Obviously of limited interest to members on here, but it can have other uses.

Your reply did prompt me to look at what other GR generating apps were available: which one do you use?

It is this one: https://grid-reference.en.aptoide.com/app

I have now installed the free GridPoint GB app which does give a 10-digit GR. When this is opened and you are stationary, you can see the GR numbers change as the GPS chip probes its circle of uncertainty every second which validates the points I made above. You need to round off the rightmost digits (which are demonstrably unreliable) to get to an 8-digit GR.

Many years ago I was sternly ticked off by an eminent botanist (sorry, that again!) who told me - in writing - that you can not round up the places when reducing the number of figures in a grid reference, like you do with decimal places in maths. My brain is currently too befuddled to go into the ins and outs of it, and I don't have any notes to quote, it is etched on my memory, but basically it puts you in the wrong square. I'll leave you to work it out.

fernman

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Re: OS maps for my new phone???
« Reply #53 on: 10:28:02, 11/09/20 »
The mists have cleared a little. If you round up an 8 figure grid ref, say SU 3248 5136, to SU 325 514, you are in then in the wrong square and you should be in SU 324 513.

Worth remembering before you plummet to your death from a cliff.

vizzavona

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Re: OS maps for my new phone???
« Reply #54 on: 14:11:57, 11/09/20 »
Hello.... Same square... All you are doing is adjusting the third digit if the fourth is greater than 5.:-)

GoneWest

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Re: OS maps for my new phone???
« Reply #55 on: 14:37:39, 11/09/20 »
Hello.... Same square... All you are doing is adjusting the third digit if the fourth is greater than 5.:-)


That depends on whether you regard the east and north boundaries as being in the "same square" as defined by the west and south boundaries. Mathematically, the former must define a different square (of whatever size). However, it's all nonsense, as you imply. Obviously, to me anyway, you should estimate your position with the best accuracy you can, but no better (to paraphrase Einstein). If this means rounding up or down, to give an honest impression of achieved accuracy, then so be it. Which grid square your particular position then falls in is of only academic interest. Anyone tryng to rescue you, for instance, would be searching within a reasonable radius of your quoted position, not treating nearby grid lines on the map as impenetrable fences on the ground!

Eyelet

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Re: OS maps for my new phone???
« Reply #56 on: 15:41:26, 11/09/20 »
...then additionally the ten digit location is preceded by another digit and East and North.  Does the East and North prior to the digits take the place of the two Alphas that we are familiar with to give a reference within the 100 Kl. 'square' of the system?


Yes, these are Eastings and Northings which give the 100km unit east and north of the grid origin - see the following link for a clear explanation: digimap.edina.ac.uk/webhelp/os/data_information/os_data_issues/grid_ref_conversion.htm.

Eyelet

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Re: OS maps for my new phone???
« Reply #57 on: 16:23:46, 11/09/20 »
I have used a Garmin eTrex H to check plant records (ferns, of course!) that have 8 figure grid references in woods and elsewhere, and every time it has been a case of go to the point, look around you and there it is within a few feet.


An 8 figure GR puts you in a ~33ft square so you are doing well to find the fern within a few feet, but then I bet you know what you are looking for! 


I should also have mentioned that one can get a more precise position fix by way point averaging. Those of you who have seen the point cloud or "spaghetti" in your recorded track where you stopped for lunch or otherwise left your phone or GPSr unit stationary for some time have simply observed the circle of uncertainty in the position fix over a period of time. Some GPSr units have a setting where you can get an average position from recording multiple points which is generally more precise than simply taking one observation. If you take the time to do this, your GR will be more precise.


fernman

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Re: OS maps for my new phone???
« Reply #58 on: 17:25:24, 11/09/20 »
Hello.... Same square... All you are doing is adjusting the third digit if the fourth is greater than 5.:-)

OK, so you're thinking of 1km squares as shown on Ordnance Survey maps and I'm thinking of smaller squares.

Let me put it another way. The grid reference I used before was made up in my head. Now for a real one. The eight figure summit of Snowdon is at SH60985437. No, I'm not that clever, I looked it up.

Now round it up to six figures, SH610544, at which point you won't be on the summit, you'll be falling down Clogwyn y Garnedd. You'll be safe on SH609543.