Tracker: Measurements

btn_tracker.png  We can measure distances and bearings in windows for maps, drawings, images, and labels using the tracker tool.   The tracker tool reports length and bearing in the status bar at the bottom of the main Manifold desktop.  Length is reported in the units (for example, feet or meters) used by the coordinate system of the active window, except for Latitude / Longitude coordinate systems, for which distances are reported in meters and not degrees.    The tracker tool computes distances and bearings over the current ellipsoid using high accuracy formulae.

Choosing the Tracker Tool

il_switch_tracker_mode01.png

 

The default mouse cursor mode is navigation.   

 

il_switch_tracker_mode02.png

 

The drop-down menu on the mode button lets us switch into tracker mode.

 

tbar_tracker_mode.png

 

The mode button always shows what mode applies for that window.   Hovering the mouse over the mode button will show a tooltip.    Different windows can have different modes, with one window being in Tracker mode while another window stays in Navigation mode.  As we switch between windows the mode button will automatically switch to show the mode for that window.

 

  <spacebar>

Press the spacebar on the keyboard to toggle snap to vertices on or off.   

Click

Click to mark a vertex in the tracker line.

Shift-click

Shift-click to terminate a branch in the tracker line.   The next click will start a new branch.

<Insert>

Press the Insert key on the keyboard to toggle Edit mode on or off.   Edit mode allows clicking on an existing vertex to make the icon bigger, allowing us to drag the vertex to a new position.   Exiting Edit mode by pressing Insert again will restart clicking new vertices after the last designated "big" vertex.

<Esc>

Press Esc key on the keyboard to start a new tracking line.

 

Commands are similar to those used for editing drawings.  For example, using spacebar to toggle snap mode on and off, Shift-click to terminate a branch, and Insert to switch into or out of editing mode are the same commands.

 

The tracker tool can tell the difference between a click to mark a vertex and a click and drag to pan the view in the usual way.    In the middle of drawing a tracker line with the tracker tool we can zoom in and out with the mouse wheel and we can click and drag to move the view around to better see where our next click should go.

 

Snapping

btn_snap_cursor.png  When the active layer is a drawing, the tracker tool will snap to vertices. Toggle snap mode on and off with the spacebar.   Snap mode is indicated with a blue box cursor that snaps to a nearby vertex.

 

 

Measuring distances and bearings with the tracker:

 

  1. Open a map, drawing, image or labels window.

  2. Click onto the cursor mode button and choose Tracker.  The button will show Tracker mode.

  3. Click the starting position for the measurement in the open window.

  4. The status bar will report distance and bearing from the starting position to the current position of the mouse cursor.

  5. Click a location to mark that as vertex in the tracker's line.   The status bar will now report total distance to the mouse cursor from the start, with bearing from the last vertex to the cursor.

  6. Press Esc to start over with a new tracker line.

  7. Click the Default mouse mode tool to end tracker mode.

 

The above procedure reports distance over a single, continuous tracker line.   If we like, we can break up the tracker line so that it consists of two or more paths, or branches, with a gap in between.   In that case the tracker will report the total distance, not counting the gap between branches.

 

Measuring distance with two or more branches:

 

  1. Open a map, drawing, image or labels window.

  2. Click onto the cursor mode button and choose Tracker.  The button will show Tracker mode.

  3. Click the starting position for the measurement in the open window.

  4. The status bar will report distance and bearing from the starting position to the current position of the mouse cursor.

  5. Click a location to mark that as vertex in the tracker's line.   The status bar will now report total distance to the mouse cursor from the start, with bearing from the last vertex to the cursor.

  6. Click as many vertices as desired for that branch.  Shift-click on the last vertex for the branch.

  7. Click to mark the starting point for the next branch.

  8. Click for as many vertices are desired for that branch.   The status bar will report total distance through both branches, not counting the gap between branches.

 

In complex measuring tasks we may have clicked many times to create a convoluted tracker line, only to realize that we missed a vertex along the way.   Rather than re-do the entire set of clicks

 

Editing a tracker line on the fly to move a prior vertex:

 

  1. Open a map, drawing, image or labels window.

  2. Click onto the cursor mode button and choose Tracker.  The button will show Tracker mode.

  3. Click the starting position for the measurement in the open window.

  4. Click locations as desired to mark vertices, to grow the tracker line.

  5. When prior vertices are to be edited, press the Insert button on the keyboard.

  6. The last clicked vertex will change into a large box.  The larger box shows the context vertex for editing.

  7. If some other vertex is to be moved, click that vertex.  It will change to a larger box to show it is the context vertex.

  8. We can now drag that vertex to a different location.

  9. To continue growing the tracker line, click the last vertex in the line to make it the context vertex.

  10. Press the Insert button again.  The tracker will switch to adding new vertices to the tracker line with each click.

 

Editing a tracker line on the fly to insert a new vertex:

 

  1. Open a map, drawing, image or labels window.

  2. Click onto the cursor mode button and choose Tracker.  The button will show Tracker mode.

  3. Click the starting position for the measurement in the open window.

  4. Click locations as desired to mark vertices, to grow the tracker line.

  5. When a new vertex is to be inserted into a prior segment, press the Insert button on the keyboard.

  6. The last clicked vertex will change into a large box.  The larger box shows the context vertex for editing.

  7. Click the vertex at the beginning of the segment where the new vertex is to be inserted.  It will change to a larger box to show it is the context vertex.

  8. Press the Insert button again. The tracker will switch to adding new vertices to the tracker with each click, rubber banding within that segment to the mouse position.

  9. Click as desired to add new vertices in that segment.  When finished, press the Insert button again. \

  10. The last clicked vertex will now be shown with a larger box.  

  11. To continue growing the tracker line, click the last vertex in the line to make it the context vertex.

  12. Press the Insert button again.  The tracker will switch to adding new vertices to the tracker line with each click.

 

 

ico_nb_arrow_blue.png

After using the tracker tool we should switch the mouse cursor mode back to default navigation mode.

 

il_switch_tracker_mode03.png

 

There is no harm done if we forget, since the tracker simply reports measurements and does not change the data in any way.  

Example

We will measure distances in a map.

 

eg_tracker01_01.png

 

The map seen above shows a drawing called Sights that indicates locations of tourist interest in Paris, marked with green points, shown on a background layer of Bing Maps with opacity set in the layers pane to 50% to provide lighter coloring.   From upper left to lower right the sights are the courtyard of the Louvre, the center of the Pont des Arts, the plaza in front of the bronze equestrian statue of Henry IV on the Pont Neuf, the entry to Sainte Chapelle, and the cathedral of Notre Dame.   In the upper right a dot marks the corner of the plaza by the Pompidou center.

 

For this example, we assume a walking tour through these locations.  We will draw a tracker line to measure the distance we walked.

 

btns_tracker_in_menu.png

 

 a_cursor_tracker.png   Choose the Tracker in the cursor mode button to enable the tracker tool.   The mouse cursor changes into the tracker cross cursor.

 

eg_tracker01_02.png

 

With the focus on the Sights layer we see that by default the blue box cursor for the tracker snaps to the location of the nearest point in the active layer's drawing.    So long as the mouse cursor is nearby the green dot in the courtyard of the Louvre the blue box cursor will snap to that point.   Clicking will mark that spot as the first vertex in the tracker line.

 

eg_tracker01_03.png

 

If we next move the  mouse cursor near the green dot on the Pont des Arts, the blue tracker cursor will snap to that location.

 

eg_tracker01_04.png

 

As the blue cursor snaps to the new location the status bar readout for the tracker tool will report the length of the tracker line in meters as well as the bearing, in degrees, from the prior vertex to the current location of the blue box cursor.  We can see that the straight line distance from the first green dot to the second is about 393 meters on a bearing of 148 degrees.   The tracker tool reports distance and bearing in the status bar to three places past the decimal point.  

 

ico_nb_arrow_blue.png  To turn snapping off, we press the spacebar.   Pressing the spacebar toggles snap mode in the tracker off and on.

 

eg_tracker01_05.png

 

We can now move the mouse cursor as we like and the tracker segment blue line will rubber-band to the current mouse location.   

 

eg_tracker01_06.png

 

Wherever we move the mouse cursor, the tracker readouts in the status bar will update continuously.   For example, the total length of the tracker blue line from the courtyard of the Louvre to the middle of the Pont des Arts to the current location of the mouse cursor in the illustration above is 653 meters, with the bearing from the tracker vertex at the center of the Pont des Arts to the current mouse cursor location being about 98 degrees.

 

ico_nb_arrow_blue.png  Press the Esc key on the keyboard to clear the current tracker line, to allow a fresh start.  

 

Straight line distances as seen above are useful in some cases, but to measure our walk through Paris we do not want to snap in a straight line, as the bird flies, from the Louvre to the center of the Pont des Arts.   Instead, with snapping off we will click a few points indicating an actual walk from the Louvre to the Pont des Arts.

 

eg_tracker01_07.png

 

In the illustration above we have pressed the spacebar to turn on snap so we can click exactly on the starting point.   We then have pressed the spacebar again to turn snap off so we could click to mark two more vertices to show a walk along the embankment of the Seine.      To click the location at the beginning of the Pont des Arts we use the mouse wheel to zoom in, so we can click more accurately.

 

eg_tracker01_08.png

 

In the illustration above we have used the mouse wheel to zoom in, and we have also clicked and dragged to pan the view to center the region of interest.    The tracker tool can tell the difference between clicking and dragging as done to pan the view, and clicking to mark a location.    We have zoomed in to the beginning of the Pont des Arts, a footbridge over the Seine.  We click at the desired location to mark a vertex.

 

eg_tracker01_09.png

 

We can continue on our path to click additional locations.   After the initial click as seen above, we can zoom out using the mouse wheel.   If we like, we can also use the back arrow or other buttons on the main toolbar to zoom back to a prior view or to zoom out.

 

eg_tracker01_10.png

 

We press the spacebar to turn snap back on so we can click exactly on the dot at the center of the Pont des Arts.    We then press the spacebar to turn snap off to continue clicking on various locations where we want to place vertices to draw a tracker line indicating our walk.

 

eg_tracker01_11.png

 

The illustration above shows the vertices we have clicked into position to draw our blue tracker line.    We have walked from the Louvre along the Seine, across the Pont des Arts, along the Seine to the Pont Neuf, across the first span of the Pont Neuf to the plaza in front of Henry's statue, and then along the Seine on the Île de la Cité.   We have stopped in to see Sainte Chapelle, and then we have walked through the flower market by the Cité Metro stop to finally arrive at Notre Dame.   

 

For the last location we have pressed the spacebar to turn snap on and then we have shift-clicked to place that vertex as the end of a branch.

 

eg_tracker01_12.png

 

The tracker readout faithfully reports the total length of the blue tracker line we have drawn as approximately 1988 meters.  The bearing is zero degrees because with snap turned on the blue cursor is snapped to the last vertex that was created, so there is no bearing from the last vertex to the blue box tracker cursor.

 

eg_tracker01_13a.png

 

Why did we Shift-click the last vertex?   That ends a branch, so the next click we do will start a new branch, that is, a continuation of the tracker line that need not be contiguous to the end of the prior branch.  In this case, when we move the mouse cursor near the green dot by the Pompidou center the tracker blue box cursor snaps to that location.   We click at that spot to place the first vertex of the next branch at that location.

 

Why use two branches?   That models a situation where we did not walk from Notre Dame to the Pompidou center, but instead we took a taxi or, more fun, we hired a bicycle rickshaw to pedal us from the Gothic beauty of the cathedral of Notre Dame to the modern self-indulgence of the Pompidou center.     Since our tracker line is intended to measure the distance we have walked, we want to skip that part of our itinerary where we rode in a cab or a rickshaw.

 

eg_tracker01_13.png

 

We press the spacebar to turn snap off, and then we continue clicking to mark vertices for our path.   We walk from the Pompidou center past Les Halles and then back down to the beginning of the Pont Neuf on the Right Bank of the Seine.   We walk along the Seine a bit and then turn right to our final destination, the Autocité parking garage entrance in front of the church of Saint-Germain-l'Auxerrois.  

 

eg_tracker01_14.png

 

The tracker readout in the status bar faithfully reports the total length of the two blue branches that make up the tracker line:  we have walked 3180 meters, approximately two miles.   That does not count the distance of our rickshaw ride from Notre Dame to the Pompidou center.

Modify the Tracker Line

Suppose now we realize that the tracker line we have marked does not accurately reflect the walking path we took.    Instead of repeating all of our work we can simply edit the existing tracker line.

 

eg_tracker01_15.png

 

Press the Insert key on the keyboard to switch the tracker tool into editing mode.

 

eg_tracker01_16.png

 

In editing mode, the context vertex is shown with a larger blue editing handle.  The context vertex may be dragged to a new location.   Clicking any vertex makes it the context vertex.   

 

For example, suppose we have remembered that after visiting the bronze statue of Henry IV we did not walk along the embankment of the Seine, but instead walked through the small park toward the center of the Île de la Cité.    We click on the vertex to be moved to make it the context vertex.

 

eg_tracker01_17.png

 

That vertex switches to a larger blue editing handle.  We can now drag it to a new location, so the tracker line follows the path we walked through the small park, the Place Dauphine, where we paused for a moment to eat a sandwich in an oasis of calm away from tourist crowds.

 

eg_tracker01_18.png

 

The new location of the moved vertex, however, does not accurately indicate our path, because the next segment is a diagonal line that does not follow the street, but which instead cuts across the Police building.   We must add another vertex.   To do that, we press the Insert key again, which takes the tracker tool out of editing mode.

 

eg_tracker01_19.png

 

Whenever the tracker tool drops out of editing mode, the mouse cursor goes "live" at whatever is the position just after whatever was the context vertex in editing mode.   In this case, when we press Insert the tracker line rubber-bands to the current cursor location from both vertices at either end of that segment.     We can move the mouse cursor about and wherever we click a new vertex will be added to the tracker line.

 

eg_tracker01_20.png

 

We position the cursor at the corner of the street where we walked and the click to place a vertex at that location.

 

eg_tracker01_21.png

 

At all times, as we move the cursor about and place vertices, the tracker tool readout in the status bar reports whatever is the total length of all branches of the blue tracker line at that moment.  We see that making the above modification takes the total length of the distance we have walked to 3239 meters, or just slightly over two miles.

Extending an Existing Tracker Line

In the steps above we have inserted a new vertex into the tracker line.  Suppose we would like to extend an existing line, picking up where we left off?  

 

To do that we press the Insert key once more to again enter editing mode.

 

eg_tracker01_22.png

 

The context vertex appears as a larger blue editing handle.   To extend that branch of the tracker line, we click onto the last vertex of the branch to make it the context vertex.

 

eg_tracker01_23.png

 

The last vertex now appears as a larger blue editing handle.   We press the Insert key again to drop out of editing mode.

 

eg_tracker01_24.png

 

The blue tracker line will now rubber band to the current cursor position.   Wherever we click we will add another vertex, extending the tracker line.

 

Copying Tracker Length and Bearing

When the tracker tool is operating, right-clicking in the map window calls up a context menu that allows us to copy the total length of the tracker line to the last-clicked location, or the bearing of the last tracker segment to the last-clicked location.

 

 

 

Consider the map above, where we have clicked twice with the tracker tool, first to start the tracker line at the Arc de Triomphe, and then second at the obelisk at the center of the Place de la Concorde.

 

eg_tracker01_26.png

 

With snapping on, the tracker readout in the status bar reports the length and bearing of the first segment marked, until a third click is made.   In this example the length is 2126.792 meters and the bearing 115.755 degrees.

 

eg_tracker01_27.png

 

If we press the spacebar to toggle snapping off, the status bar readout for the tracker will follow the cursor and report the current total length and current bearing.

 

eg_tracker01_28.png

 

For example, if we move the cursor in the direction of the Place de la Madeleine, the status bar will report the increased length to the cursor and the bearing of approximately 27 degrees.

 

eg_tracker01_29.png

 

We can right-click into the map and choose Copy Length to copy to the Clipboard the length of the tracker line to the last clicked vertex.   

 

2126.7924393029534

 

Pasting it wherever we want, we can see the length is the full-precision equivalent of the 2126.792 value that was reported for the length of the first segment in the status bar.

 

115.75513980334591

 

Likewise, if we had chosen Copy Bearing from the context menu, we would have copied the bearing of the last segment, that is, to the last-clicked vertex.   Pasting it, we get the full precision equivalent of the 115.755 degrees bearing reported previously in the status bar.

 

The length copied is always for the length of the tracker line to the last-clicked vertex.   The bearing is always the bearing of the last segment, that is, from the next-to-last-clicked vertex to the last-clicked vertex.

 

Notes

Works in all windows - The tracker tool works in all visual windows.   The illustrations show the tracker in action within a drawing layer in a map, to provide a simple illustration of how snap works.   The tracker also works with images and labels layers, too.   

 

High accuracy - Manifold's tracker tool computes distances using Vincenty algorithms to compute the distance over the surface over the actual ellipsoid used in the datum for the active component.   That provides significantly greater accuracy than computing distance over a generic sphere or planar computations.   Whatever coordinate system is used for the active component is automatically reckoned as part of the computations.   

 

Antipodal limitation - The Vincenty algorithms utilized become degenerate when measurements are made between two antipodal locations, that is, locations which are at nearly exactly opposite parts of the Earth, for example, between Punta Arenas, Chile, and the Western shore of Lake Baikal.  Therefore, we should not use the tracker tool to measure between vertices that are placed at nearly exactly antipodal locations on Earth.

See Also

Getting Started

 

Maps

 

Drawings

 

Editing Drawings

 

Layer Opacity

 

Images

 

Labels

 

Style