Extract points from location on screen relative to center of screen which equals current location.

There is an onTap function in an input delegate (https://developer.garmin.com/connect-iq/api-docs/Toybox/WatchUi/InputDelegate.html) which passes the coordinates of the tap on the screen. I'm not sure how accurate it is, but it's accurate enough to draw and tap on a button, so it should be possible.

You can save pioints to storage and connect them by drawing lines.

You can calculate the location in lat/long using some simple ratios and trigonometry based on the distance on the screen. I doubt the distances would be large enough to worry about accurately modelling the curvature of the Earth

Do you envisage drawing a map to the screen to allow them to tap on? I have written a map app (Mappily). If you just want to draw an image with North Up, that should be pretty straightforward. If you want a rotating map, that was a huge amount of work. 

So basically i’ve modified code from tskfs offline map datafield into a widget, it’s a static north up map, (equirectangular) divided into multiple images. You cannot interact with it like a proper garmin map but it changes according to your gps position. 

I can do the input delegate stuff no problem as i’’ve already got an inupt delegate, its knowing all the other stuff, maths isn’t my strongest point.

That's a good start. It's not too complicated maths so you should be fine.

Say the screen is 400x400 pixels. Your position is in the centre at x=200, y=200. If you click at x=50, y=100 you need to work out the x difference and y difference, which is 200-50=150 and 200-100=100. 

Now, you know your current GPS position in latitude(y) and longitude(x) in degrees. All you need to do is work out the number of degrees of lat and long in 150 and 100 pixels respectively to find the position in latitude and long of your point, which you can store.

This depends on the zoom of the map. Imagine the map is really zoomed in, you'd see less of the map and the screen would be less 'degrees' wide and high.

If the map is 10 degrees longitude wide (that's one big map!) then 150 pixels is 10* 150/400 degrees wide. You subtract that from your longitude to get the longitude of the point you clicked. Same principle with latitude.

If I get a little time tomorrow I'll knock up an example for you.

You'd also need a function to do the opposite so you can convert the lat and long back to pixels on the screen to draw the points and lines.

Ooh, this is really helpful, yes it is a big map 3000x3000px, it’s been chopped up into 144 parts. 0.png to 143.png

This is a smaller coloured version

I have coded in the mildly complicated calculations and they work like a charm, next thing is figuring out how to save a bunch of points in a storage friendly way then load them as a track, any tips? Ideally as well said track would be remembered until you cleared it.

Only the same app that writes something to storage can read that storage.  Storage can not be shared between apps.

CIQ apps can not use standard tracks/courses/waypoints.

I am not using standard course/tracks/waypoints stored on the stock garmin navigation app, I am extracting multiple lat longs from a tap of the screen in my own app and wish to save them in my app as well as show them in my app connected as a track to follow.

you can store them as just lat/lon pairs, using a key per pair, or store them as an array of pairs with one key.

Could I trouble you for an example please?

//build array of points

var points = [lat1,lon1,lat2,lon2,lat3,lon3];

//save to storage

Application.Storage.setValue("pointskey",points);