Reading Coordinates from Drakensberg Maps
09 Mar 2021 15:53 #76588
by Braks14
Reading Coordinates from Drakensberg Maps was created by Braks14
Good day,
I am not sure where to post this, feel free to point me in the right direction if this has already been covered.
My question is with regards to the "official" Drakensberg maps, see picture below.
These are in 1:50 000 scale and advised to set your coordinates on GPS to hdd.mm.mmmm
They clearly show the Latitude and Longitude in dd.mm, my question is how does one calculate the .mmm decimals as to be closer to actual location ?
The gridlines on the map measure 37 x 32mm
Much appreciated.
I am not sure where to post this, feel free to point me in the right direction if this has already been covered.
My question is with regards to the "official" Drakensberg maps, see picture below.
These are in 1:50 000 scale and advised to set your coordinates on GPS to hdd.mm.mmmm
They clearly show the Latitude and Longitude in dd.mm, my question is how does one calculate the .mmm decimals as to be closer to actual location ?
The gridlines on the map measure 37 x 32mm
Much appreciated.
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11 Mar 2021 03:19 - 11 Mar 2021 03:21 #76595
by intrepid
Take nothing but litter, leave nothing but a cleaner Drakensberg.
Replied by intrepid on topic Reading Coordinates from Drakensberg Maps
It's been many years since I've measured a coordinate off the map to punch it into my GPS (I assume this is what you are trying to do?). To be honest I've forgotten what measuring technique I used.
Have you considered using a digital map source such as Open Street Maps and simply eye-balling a coordinate on there based on what feature you are wanting from the paper maps? The contour lines should be very similar so you can probably get it as accurate as measuring it with a ruler on the paper. I have done this too in the past.
Alternatively, are you looking for the coordinates of a specific feature? Maybe the community here can easily supply you with that.
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Have you considered using a digital map source such as Open Street Maps and simply eye-balling a coordinate on there based on what feature you are wanting from the paper maps? The contour lines should be very similar so you can probably get it as accurate as measuring it with a ruler on the paper. I have done this too in the past.
Alternatively, are you looking for the coordinates of a specific feature? Maybe the community here can easily supply you with that.
Take nothing but litter, leave nothing but a cleaner Drakensberg.
Last edit: 11 Mar 2021 03:21 by intrepid. Reason: typo
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11 Mar 2021 10:05 #76597
by BobbyStanton
Replied by BobbyStanton on topic Reading Coordinates from Drakensberg Maps
You need to just guesstimate the fractions of minutes between the grid lines. The red dashed lines which criss-cross the map are the red coloured units on the outside of the map. There are numbers in black which are on the inside of the map but these are in metre units for the Mercator projection and should probably be ignored for most purposes.
It is more important to set up your GPS to match the projection of the map otherwise large errors can occur. The projection of the EKZNW maps is stated at the bottom just inside the outer graticule. On this map it is Gauss Conform Projection (more or less the same as Mercator), Central Meridian 29E, Clarke 1880 Spheroid. You don't need all that to set up your GPS. On a Garmin Etrex series GPS go to 'Setup" -> 'Map datum' and select 'Cape'. Then go to 'Setup' -> 'Units' -> 'Position format' and choose 'hddd mm.mmm". Remember to set it back to WGS84 if you are using that type of map. All map data is stored internally in the GPS receiver in decimal degrees (dd.ddd) and WGS84 so if you dump the data to another device, eg. computer mapping software, it will be in decimal degrees. It is only displayed on the fly in your chosen units and datum.
Apologies if this sounds like I am talking down to you but it may help others who are struggling with this technology. It can be quite a mystery to some.
It is more important to set up your GPS to match the projection of the map otherwise large errors can occur. The projection of the EKZNW maps is stated at the bottom just inside the outer graticule. On this map it is Gauss Conform Projection (more or less the same as Mercator), Central Meridian 29E, Clarke 1880 Spheroid. You don't need all that to set up your GPS. On a Garmin Etrex series GPS go to 'Setup" -> 'Map datum' and select 'Cape'. Then go to 'Setup' -> 'Units' -> 'Position format' and choose 'hddd mm.mmm". Remember to set it back to WGS84 if you are using that type of map. All map data is stored internally in the GPS receiver in decimal degrees (dd.ddd) and WGS84 so if you dump the data to another device, eg. computer mapping software, it will be in decimal degrees. It is only displayed on the fly in your chosen units and datum.
Apologies if this sounds like I am talking down to you but it may help others who are struggling with this technology. It can be quite a mystery to some.
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