How to find pixel coordinates ?

[FredT]

Hi,

I would like from a custom image loaded in a GMap3, find pixel coordinates of a Marker in the Marker OnDragEnd event.

For this I use the method described here:
https://developers.google.com/maps/documentation/javascript/examples/map-coordinates
But I do not get the right pixel coordinates!
Have I forgotten something ?
Or is there another method ?

Here is my code:

Code: Select all

procedure TIWForm1.IWAppFormCreate(Sender: TObject);
var
    L: TstringList;
    LMarker: TIWCGJQGMap3MultipleMarker;
begin
    IWCGGoogleLibLoader.GoogleApiKey:= '...';
    IWCGJQGMap3.JQGMapV3Options.ImageMapType.Id := 'test';
    IWCGJQGMap3.JQGMapV3Options.ImageMapType.Options.MaxZoom := 7;
    IWCGJQGMap3.JQGMapV3Options.ImageMapType.Options.MinZoom := 3;
    IWCGJQGMap3.JQGMapV3Options.ImageMapType.Options.Name := 'test';
    IWCGJQGMap3.JQGMapV3Options.ImageMapType.Options.TileSize.Width := cTILE_SIZE;
    IWCGJQGMap3.JQGMapV3Options.ImageMapType.Options.TileSize.Height := cTILE_SIZE;
    IWCGJQGMap3.JQGMapV3Options.Map.Options.MapTypeCustomId := 'test';

    L := TStringList.Create;
    L.LoadFromFile(WebApplication.ApplicationPath + 'myMap.js');
    IWCGJQGMap3.JQGMapV3Options.ImageMapType.Options.GetTileUrl.Script := L.Text;
    L.Free;

    // Markers
    LMarker:= IWCGJQGMap3.JQGMapV3Options.Marker.Values.Add;
    LMarker.Data:= 'Marker 0';
    LMarker.Id := '0';
    LMarker.LatLng.Latitude:= 20;
    LMarker.LatLng.Longitude:= -10;
    LMarker.Options.Draggable := True;

    IWCGJQGMap3.JQGMapV3Options.Marker.Events.OnDragEnd.OnEvent:= GetCoordMarkerDragEndEvent;
end;

procedure TIWForm1.GetCoordMarkerDragEndEvent(Sender: TObject; AParams: TStringList);
var
    lat: Double;
    long: Double;
    myFormatSetting: TFormatSettings;
    LatLng: TIWCGJQGMap3LatLng;
    WorldCoord, PixelCoord: TPoint;
    iZoomLvl: Integer;
    x, y: Double;
begin
    myFormatSetting.DecimalSeparator:= '.';
    lat:= StrToFloat(AParams.Values['markerLat'],myFormatSetting);
    long:= StrToFloat(AParams.Values['markerLng'],myFormatSetting);

    LatLng := IWCGJQGMap3.JQGMapV3Options.Map.Options.Center;
    LatLng.Latitude := lat;
    LatLng.Longitude := long;

    WorldCoord := Project(LatLng);

    iZoomLvl := IWCGJQGMap3.JQGMapV3Options.Map.Options.Zoom;
    x := Floor(WorldCoord.X * Power(2, iZoomLvl));
    y := Floor(WorldCoord.Y * Power(2, iZoomLvl));

    PixelCoord := Point(Trunc(x),Trunc(y)); // Bad Coord !

    // ...
end;

function TIWForm1.Project(ALatLng: TIWCGJQGMap3LatLng): TPoint;
var
    siny: Double;
    x, y: Double;
begin
    siny := Sin(ALatLng.Latitude * PI / 180);
    siny := Min(Max(siny, -0.9999), 0.9999);

    x := cTILE_SIZE * (0.5 + ALatLng.Longitude / 360);
    y := cTILE_SIZE * (0.5 - System.ln((1 + siny) / (1 - siny)) / (4 * PI));

    Result := Point(Trunc(x),Trunc(y));
end;


Thank.

[Alexander Bulei]

Hi FredT,

I think the problem is in zoom, i guess its not updated...you need pass the current zoom of map into your drag function.

Debug to verify that.

Best Regards.

[FredT]

Hi,

The zoom value I get at the OnDragEnd is updated, I get values ​​from 3 to 7, which corresponds to the min and max zoom.

I wonder if the problem does not come from the centering of the map: when I created a marker with latitude 0 and longitude 0, it should I think to be in the center of the map but it does not appear.

I tried this but it does not change anything:
GMap3.JQGMapV3Options.Map.Options.Center.Latitude:=0;
GMap3.JQGMapV3Options.Map.Options.Center.Longitude:=0;

Thank

[Alexander Bulei]

Hi FredT,

Please send me the simple testcase project.
TIA

Best Regards.

[FredT]

Hi,

I send you the link to download the test project compressed with 7-zip (13Mo) to support@cgdevtools.com with object: "How to find pixel coordinates ?" because i can't put it in attachment.
To test, drag and drop a marker, I calculate the pixel coordinates in the function GetCoordMarkerDragEndEvent.

Thank.

[Alexander Bulei]

Hi FredT,

Since it's not related to our comps, I will charge the premium support ticket.
Let me know, if you agree with that.

Best Regards.

[FredT]

Hi Alexander,

Yes, we agree to open a ticket.

Thank.

[Alexander Bulei]

Hi FredT,
Please check the changed files.

Best Regards.

[FredT]

Hi Alexander,

Indeed it is always better to use the right types, however the values ​​returned are identical.

I will detail a little more what I wish to do:
In zoom 3 my image is composed of 2 * 2 tiles, the size of a tile is 208 * 208 pixels, so my image is 416 * 416 pixels.
When I drag'n drop the marker at the top left edge of the image I get the pixel coordinates (506, 506) and when I drag'n drop it to the top right edge I get (843, 506).

With these coordinates I get a width of 843 - 506 = 337 or the image is a width of 416, so it's wrong.

Ideally I would like to get for the top left edge (0, 0) and for the top right edge (416, 0).

Thank.

[Alexander Bulei]

Hi FredT,

As you can see, the pixel coordinates now are same as google...
If it doesnt work for you, you need find another calcs for your needs.

Best Regards.