How do I draw multiple points from multiple lat longs pairs?

I have an array in storage called track, it looks a bit like this.

[56.8967, 0.7654, 53,8736, 0.9832, 50,6453, 0,0773….etc]
As you can see, multiple lat and longs, the array is of no fixed size.

Currently I have only managed to draw the first lat lon in the array.

//By transforming them with this:


function TransformCoordinates(lat, lon) {

var Me = [240/2,240/2];

var track = Application.Storage.getValue(“track”);

var pixelsLong = (120 - lon) * (4/screenWidthPixels);

var pixelsLat = (lat - 120) * (4/screenHeightPixels);

var x = Me[1] - pixelsLong;

var y = Me[0] - pixelsLat;

return [x,y]; }

//Then drawing them with this:

function onUpdate(dc) {

var track = [x,y];

dc.setColor(Graphics.COLOR_BLACK, Graphics.COLOR_TRANSPARENT);

for(var i=0; i<track.size();i=i+2){
var pointA=track[i];

var pointB=track[i+1];

dc.setPenWidth(8) 

dc.drawPoint(pointA,pointB);}

Help in drawing all these points is much appreciated.

0 Alan.raceQs over 4 years ago

Scarecrow123 said:
56.8967, 0.7654, 53,8736, 0.9832, 50,6453, 0,0773….etc]

Typo? In your array, you show commas not fullstops as decimal separator in 53,8736 and 50,6453

And you may be getting issues with numbers (integers) and floats. Look at the values of pointA and B through the debugger.

0 Scarecrow123 over 4 years ago in reply to Alan.raceQs

Thats a typo from typing quickly on a phone.

0 Alan.raceQs over 4 years ago in reply to Scarecrow123

OK, so what did you find when you checked the values in the debugger?

0 Scarecrow123 over 4 years ago in reply to Alan.raceQs

I’m afraid i’m away from my computer for a bit that has eclipse and thus the project on it, however I did have the foresight to println pointA and pointB and both return as 120. This places it (by it I mean the first point) right in the middle of the screen. The others do not seem to get transformed nor drawn.

0 subra over 4 years ago

I don't understand the logic of scaling in your code snippet.

var pixelsLong = (120 - lon) * (4/screenWidthPixels);
var pixelsLat = (lat - 120) * (4/screenHeightPixels);

This means that you reduce the difference of the angles lat/lon by a factor of 60, i.e. 4/240=0.017. If you move at running speed, all measurement points will be superimposed. To see a track on the display in this case, you need a difference of lat/lon of about 60deg/s, which corresponds to a speed for movement around the world in 6s.

So the scaling isn't appropriate and it depends on the speed.

0 Scarecrow123 over 4 years ago in reply to subra

Would you be willing to provide an example I can use instead to draw the points? I’m not very good at maths. Also as i’m projecting said route on an equarectangular map(non map device) is there a necessary calculation needed to do so?

0 Scarecrow123 over 4 years ago in reply to subra

Also perhaps the scaling may be off because the map is just europe as opposed to the world? Anyway that bit of codw coemf rom another post of mine where I had some help but didn’t quite work out.

0 subra over 4 years ago in reply to Scarecrow123

Scarecrow123 said:
Would you be willing to provide an example I can use instead to draw the points?

I'm not sure what you want to display but I think a general method may be something like outlined in this pseudo code:

// calculate max and min values for lons and lats
var lonMax = -180.0;
var lonMin =  180.0;
var latMax =  -90.0;
var latMin =   90.0;
for(i=0; i < track.size(), i++) {
    lonMax = (lonMax > lon[i]) ? lonMax : lon[i];
    lonMin = (lonMin < lon[i]) ? lonMax : lon[i];
    latMax = (latMax > lat[i]) ? latMax : lat[i];
    latMin = (latMin < lat[i]) ? latMax : lat[i];
}

// scale the geographical size to the display size
var scaleX = dc.getWidth() / (lonMax - lonMin);
var scaleY = dc.getHeight() / (latMax - latMin);
var scaleXY = (scaleX < scaleY) ? scaleX : scaleY;

for(i=0; i < track.size(), i++) {
    // calculate point locations in pixels
    var pixelsLon = (lon[i+1] - lon[i]) * scaleXY;
    var pixelsLat = (lat[i+1] - lat[i]) * scaleXY;

    // adjust point locations to a reference point
    var displayX = pixelsLon + pixelsXRef;
    var displayY = pixelsLat + pixelsYRef;

    // draw points
    dc.setColor(...);
	dc.fillCircle(displayX, displayY, 2);
}
...

0 Scarecrow123 over 4 years ago in reply to subra

Where it says scale the geographical size to the display size does that mean fitting the whole route scaled down into the screen as opposed to it extending off screen like in a satnav?

0 Scarecrow123 over 4 years ago in reply to subra

I’ve typed the code in, I had to define lat, lon as the variable track[0] and track[1], and define track as Application.Storage.getValue(“track”).

I’m not sure if that’s the right way to do it or not but if it is then I’ve run into a problem, it complains about them being doubles and not an array. I know in storage they are saved as doubles but in the code I save it to an array. I’m not took sure what to do.