OS map app: GR and altitude

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 Flinticus 14 Apr 2022

Have started using OS mapping app.

As a long time Viewranger user, I like that that app gives you height and GR whereas the OS map does not that I can find. Which seems a big omission.

Can I get my screen to display that data? 

Ta

 Glyno 14 Apr 2022
In reply to Flinticus:

hold your finger on the map screen for grid ref, not sure about height

Post edited at 15:39
 alibrightman 17 Apr 2022
In reply to Flinticus:

The OS Locate app gives you GPS altitude.

 colb 17 Apr 2022
In reply to Flinticus:

Found viewranger app gave accurate height based on your location. I seem to remember being asked to and downloading database of heights for the viewranger maps. Otherwise although OS locate gives GPS altitude this is not always accurate.

Using OS maps or Outdooractive I check the altitude based on the map contour for your location. long press seems to give location only.

 HardenClimber 17 Apr 2022
In reply to alibrightman:

The altitude on OS locate is calculated on an ellipsoid model so it is often 50metres different from mapping we usually use (orthometric height).

For practical purposes the altitude it gives is wrong. (OS say they are going to change this).

 alibrightman 20 Apr 2022
In reply to HardenClimber:

Interesting.  I'm surprised it's as much as 50 metres.

I started using OS Locate for altitude after noticing that ViewRanger (or at least, the version on my 10-year-old phone) is often way out when on summits in the Highlands.  My guess is that this due to calculating altitude from a digital elevation model, with insufficient resolution to handle the case where one is close to a steep drop.

From memory, OS Locate seemed to give a value within 2 or 3 metres of the summit height read from the map.   

 ianstevens 20 Apr 2022
In reply to alibrightman:

Yup, it uses the underlying DEM which OS use to make contours and the like. Not sure what is being spoken about above.

 DaveHK 20 Apr 2022
In reply to Flinticus:

It gives altitude on the website when you drop a pin but not the app. Another annoying thing about the app is that when you drop a pin it zooms right in and when you try to zoom out the pin disappears.

 HardenClimber 20 Apr 2022
In reply to alibrightman:

Yes, the magnitude of the difference is quite surprising when I've compared it at various locations. You don't need to guess why the readings are different, it is how OS decide on zero as their  'reference' .

Post edited at 23:38
 HardenClimber 20 Apr 2022
In reply to ianstevens:

Altitudes are measured relative to a theoretical baseline.

OS say that OS locate uses an ellipsoid model rather than a geoid, which is why it gives different readings (note, I didn't say incorrect).

See: https://en.wikipedia.org/wiki/Orthometric_height


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