How do I draw a simple heading arrow in the centre of the screen?

Sorry for not getting back to you, I’ve managed to produce something that looks like a compass needle and it appears to follow compass heading (sometimes) until you turn on gps at which point it goes funny. I’m not sure how you find a direction in monkey c (i’m not very good at coding). My device is a vivoactive 3 if that helps.

Also here is the source code. https://github.com/tskf/MapOfflineGPS/blob/master/map.mc

Thanks

I have failed to fully reverse engineer your code, but it seems you're using Activity.getActivityInfo().currentLocation, which returns your current position (latitude, longitude), which I can't visualise as a compass needle. 

you're asking for a "direction", but given the preceding discussion, It's not clear which direction you are after.

If you want direction of travel, then you should be using Position:info:Heading

If you're after the orientation of the device to Magnetic North, you need to use Sensor.Info.mag to get the magnetometer readings for each of the devices axes of the device and then use  Sensor.Info.accel to determine the orientation of the device. 

Alan.raceQs said:

I have failed to fully reverse engineer your code, but it seems you're using Activity.getActivityInfo().currentLocation, which returns your current position (latitude, longitude), which I can't visualise as a compass needle. 

Yes, it seems that the previous code posted here was closer to the right track:

https://forums.garmin.com/developer/connect-iq/f/discussion/279455/how-do-i-draw-a-simple-heading-arrow-in-the-centre-of-the-screen/1340504#1340504

function onUpdate(dc)

    { var g = Activity.getActivityInfo().currentLocation;

        var width;

        var height;

        var screenWidth = dc.getWidth();

        var heading = Activity.getActivityInfo().currentHeading;

...

minuteHandAngle = (heading / 1.0) * Math.PI * 2;

Alan.raceQs said:

If you want direction of travel, then you should be using Position:info:Heading

If it's a data field, you could also use ActivityInfo.currentHeading.

I did use activityinfo.currentHeading. Sorry if that wasn’t too clear. Activity.getactivityinfo().current location at the fop is actually fir a different part if the code to do with the map tskf implemented.

Scarecrow123 said:

I did use activityinfo.currentHeading. Sorry if that wasn’t too clear. Activity.getactivityinfo().current location at the fop is actually fir a different part if the code to do with the map tskf implemented.

I get that, but:

Scarecrow123 said:

Also here is the source code. https://github.com/tskf/MapOfflineGPS/blob/master/map.mc

You make it sound like that's the code you want us to look at at, but of course, that's the code that your code is *based* on, which has no reference to ActivityInfo.currentHeading.

Also, I'm not sure about this code that you posted:

minuteHandAngle = (heading / 1.0) * Math.PI * 2;

        targetDc.fillPolygon(generateHandCoordinates(screenCenterPoint, minuteHandAngle, 70, 0, 2));

generateHandCoordinates looks like this:

    function generateHandCoordinates(centerPoint, angle, handLength, tailLength, width) {

        // Map out the coordinates of the watch hand

        var coords = [[-(width / 1), tailLength], [-(width / 4), -handLength], [width / 5, -handLength], [width / 1, tailLength]];

        var result = new [4];

        var cos = Math.cos(angle);

        var sin = Math.sin(angle);

Given that currentHeading is already in radians, and Math.cos() / Math.sin() take an angle in radians, why multiply by 2 pi?

Maybe try changing your code to this:

minuteHandAngle = heading;

EDIT: or, more likely:

minuteHandleAngle = heading + Math.PI;

See forums.garmin.com/.../1342361

EDIT: after further reflection, I think it should actually be:

minuteHandAngle = heading;

Okay, looking at the Analog sample, I see why you multiplied by 2 pi:

But you have to realize that currentHeading is already an angle in radians. The code in the analog sample is doing something which is unrelated to your task: converting the position of an analog clock's minute hand into an angle in radians.

FlowState said:

Maybe try changing your code to this:

minuteHandAngle = heading;

The only thing to note here is that currentHeading ranges from -pi and pi radians (sadly not documented), whereas the Analog sample takes an angle which ranges from 0 to 2 pi.

So you may have to adjust the code slightly:

minuteHandleAngle = heading + Math.PI;

I haven't really looked at the Analog sample in depth, but it seems like you'd have to make that adjustment to make currentHeading work with the code you used from the sample.

Thats helpful! I’ll try it tomorrow. Thankyou

So this is what I did, at first I tried what you said

minuteHandAngle = heading + Math.PI

It kept returning an error until I realised I need curved brackets like this (heading + Math.PI.)

The next problem I ran into was the arrow was pointing South when facing North so I just added a minus sign in front of the number that controls the height of the arrow. Now all I got to do is test with gps, hopefully it works. Pleased so far though.

Edit: Removed the word prime.

I'm glad it's working for you, but I'm not sure I understand this:

Scarecrow123 said:

So this is what I did, at first I tried what you said

minuteHandAngle = heading + Math.PI

It kept returning an error until I realised I need curved brackets like this (heading + Math.PI.)Prime

I did have a typo where I typed "Math.Pi" instead of "Math.PI".

I'm not sure how "(heading + Math.PI.)Prime" would work. That doesn't look like valid code.