After R&D confirmed that my first ideas are not so good, have an additional idea to use some virtual arrow which is attach on your device and you will try to touch with the pick the desired point of the surface when you move the device around in space. For example, you can set different length of this arrow for different distances to the object.
So, when you think you have the correct location then e.g. confirm with a button, or other kind of command.
The idea how to implement it / no sure if this work and requires some tests/ is to use the ml3dRenderer.setupTrackingEventsCommand() callback function
This function will deliver the vectors for the current eye position, the normal view vector and the up vector. So you can find out what is your current position in regards of the world coordinates system and then calculate the position of the arrow pick. You need also to consider the position of the your model widget if it is not at 0,0,0
An example of the usage of the mention callback function is here:
////////////////////////////////////
$rootScope.$on('modelLoaded', function() {
$scope.check_if_works=false
//=====================
// set some properties
//the next prop is important that the tracking event will use the callback
$scope.setWidgetProp('3DContainer-1','enabletrackingevents',true);
$scope.setWidgetProp('3DContainer-1','dropshadow',true);
$scope.setWidgetProp('3DContainer-1','extendedtracking',true);
$scope.setWidgetProp('3DContainer-1','persistmap',true);
console.log("now check again the setting of the envronment")
console.warn($scope.app.view.Home.wdg['3DContainer-1'].enabletrackingevents)
var enabletrackingevets= $scope.app.view.Home.wdg['3DContainer-1'].enabletrackingevents
if( enabletrackingevets) $scope.setWidgetProp('3DLabel-2', 'text', "3Dcontainer.enabletrackingevents=true");
//====================
$timeout($scope.setMyEYEtrack(), 2500) //call with delay 2.5 sec
});
/////////////////////////////////////////////////////
////////////////////////////////////////////////////////////
$scope.setMyEYEtrack= function() {
if(tml3dRenderer)
{
try {
tml3dRenderer.setupTrackingEventsCommand (function(target,eyepos,eyedir,eyeup) {
if (!$scope.check_if_works) //check if setupTrackingEvents is working fine -at least one time called
{
$scope.check_if_works=false
//this below make sense only for testing
$scope.setWidgetProp('3DLabel-1', 'text', "callback setupTrackingEventsCommand is OK");
}
var scale=2.0; //distance to eye
//moved the widget in regards of the new viewpoint position of the device
$scope.setWidgetProp('3DImage-1', 'x', ( eyepos[0]+eyedir[0]*scale));
$scope.setWidgetProp('3DImage-1', 'y', ( eyepos[1]+eyedir[1]*scale));
$scope.setWidgetProp('3DImage-1', 'z', ( eyepos[2]+eyedir[2]*scale));
$scope.$applyAsync();
},undefined) } catch (e) { $scope.setWidgetProp('3DLabel-1', 'text', "exception=");}
}else
$scope.setWidgetProp('3DLabel-1', 'text', "null tml3dRenderer object on HoloLens");
} ////// finish setEYEtrack
