The example shows how to create parcels from plat maps and survey documents that describe traverses, using industry-standard Esri traverse files. Also called "metes and bounds" descriptions, traverses are widely used in surveying in the US to define parcels and lines by describing a sequence of directions, distances and curves from a starting point. Manifold automatically handles both tangent and non-tangent curves and the full variety of options used to specify angles, distances and curves. See the Traverses topic for an illustrated guide to understanding traverses, as well as for examples showing how to create a traverse interactively by creating a new line or new area.
See the video version of this example: Create Parcels from Traverse Files The video shows how this entire example can be done in less than five minutes.
We will create a parcel in a drawing by loading the parcel's coordinates from an Esri-standard traverse file. The parcel is shown in the plat map illustrated below.
The plat map is annotated with the surveyor's hand writing, specifying the parcel by writing out the traverses, that is, the sequence of lines and curves, which comprise the boundary line of the parcel, beginning with a starting point indicated by the magenta arrow. Line segments are specify by giving the bearing and length of each segment. Curves are marked with a letter and are specified in a table of curves for this portion of the plat map.
The hand written table of curves appears above.
As described in the Info Pane: Coordinates topic, Esri Traverse File Format provides a variety of notation options to write down the above surveyor's description in a standard format. The example traverse file in this topic uses Quadrant Bearing style for directions, since that is closest to the surveyor's notes, with values that can be read directly from the notes in the plat map.
We open the example traverse file in Notepad, as seen above. The text it contains:
DT QB
DU DMS
SP 1988341.77383 13782687.05291
DD n63-35-1e 271.47
DD n72-49-1e 154.23
DD n72-49-1e 15
DD n43-28-1e 67.13
TC D 95-26-2 A 41.64 R
TC D 47-7-2 A 137.57 L
DD s88-12-59e 123.49
NC c 112 D 154-21-57 c s76-30-0e L
DD s27-25-14w 810.47
DD n51-32-16w 252.56
DD n46-36-24w 192.83
DD n36-6-11e 145
DD n49-58-59w 287
The first two lines specify use of Quadrant Bearing style, QB, for directions, and degrees, minutes, seconds, DMS, format for angles. The third line specifies the coordinates of the starting point, SP, for the traverse, given in the coordinate system in which the traverse will be used.
In this case, the traverse will be used in the EPSG 3674 coordinate system, the EPSG code for the NAD83 Texas South Central state plane coordinate system with units in US survey feet. For the starting point - and all that follows - to make sense, we must use the same, EPSG 3674 coordinate system for the drawing in which we will create a parcel from this traverse.
To create a parcel from a traverse all we need in our project is a drawing. However, it is convenient to create a map within which we can have our drawing as well as a background layer, to provide visual context for what we are doing. We therefore will begin by creating a map.
To fit into this documentation, illustrations show an artificially small Manifold desktop, with only a few panes, docked to the right side. In real life we use a much larger Manifold desktop, and all panes would be turned on, with some panes docked to the left and others docked to the right.
Using the quick procedure shown in the Example: Create Maps topic, we have created a map, called Map, that uses a Google Satellite image server as a base layer. The New Map dialog automatically creates both the map and the Google satellite data source that is used as base layer in the map. The map is shown in the illustration above.
We created the map using Pseudo-Mercator projection, the same as Google.. If we like, we can leave the map in Pseudo-Mercator. If we add a drawing to the map that uses the EPSG 3674 coordinate system, the map will re-project on the fly the contents of that layer, for display purposes, into the Pseudo-Mercator projection used by the map.
That is OK, but if we want the parcel as seen in the map to be displayed using the same EPSG 3674 coordinate system as the plat map from which the traverse file was written, we can change the projection used by the map to EPSG 3674 coordinate system.
To change the coordinate system
used by the map window, we switch to the Info pane and click the coordinate
system picker button for the map.
We choose More...
In the Coordinate System dialog, we click the EPSG tab, and then we click into the filter box. We will enter the EPSG number to quickly reduce the vast list of options to just the one EPSG coordinate system we want.
Enter 3674 into the filter box and the dialog filters down to only those items in the long list that have 3674 in their name. That is the system we want, so we press OK.
Instantly, the map window changes to show a wild display. No need to panic. The state plane coordinate system for South central Texas is based on the Lambert Conformal Conic projection, which creates such a circular display when used with a "whole Earth" data set like Google satellite.
What we see is Manifold re-projecting, on the fly, Google satellite for the entire world into the Lambert Conformal Conic projection used within EPSG 3674.
We zoom into the US by right-clicking and dragging a zoom box.
That provides a more sensible view, zooming closer into the region for which the Lambert Conformal Conic projection makes sense. We now see most of North America in the Lambert Conformal Conic projection used by EPSG 3674, the state plane projection for South central Texas. The Google background layer is still in Pseudo-Mercator, but Manifold is automatically re-projecting the Google satellite image tiles into the EPSG 3674 projection used by the map window, and doing that faster than Google can serve the tiles, so there is no lag from the re-projection on the fly.
We right-click into an empty portion of the Project pane and choose Create - New Drawing.
In the New Drawing dialog, we enter Parcel as the name for the new drawing.
We click the coordinate system
picker button to choose EPSG 3674
as the coordinate system for the new drawing, using dialogs identical
to those we used to choose EPSG 3674 as the coordinate system for the
map.
Press Create Drawing.
We drag and drop the new Parcel drawing into the map.
Using the Style dialog and applying techniques like those shown in the Example: Line Style with Multiple Effects topic, we style lines in the new drawing to use alternating bright green and black dashed color with a thickness of two points. That style will ensure that any parcel lines we draw will be clearly visible.
Creating a parcel from a traverse file is a two-step process: we first create a line object, and then we open that line object for editing and replace it with the contents of the traverse file. The line object can be any line at all.
We begin by zooming into the approximate region in Texas where we know the new parcel will be created. Usually when creating parcels from traverse files we know approximately where the parcel will be created. For example, we might be creating digital plat maps or parcel layers from paper maps, so we know where the parcels are supposed to be. See the Notes below for the process if we do not know in advance approximately where the parcel will be created.
We switch cursor mode into Create Line mode.
We click five times quickly and
then we right-click and choose
Save Changes to create a line.
Important:
We click on the cursor mode button in the main menu and switch back to
Default cursor mode.
We have created a new line, which appears in the crisp, clearly visible style we specified for lines in the Parcels layer. This line is just a placeholder and could be any line at all. If we liked, we could have created it with just two clicks, a single straight line segment.
We now will replace the placeholder line with the parcel boundary line specified by the traverse file.
Alt-click the line to pick it for editing. The Info pane will pop open to the Values tab
Click the Coordinates tab and press the Load button in the toolbar.
Navigate to the desired traverse file, click it and press Open. We can also simply double-click the traverse file to open it.
Traverse files can be named using whatever names we like. They are simply text files. However, it is wise to give them names that automatically document what is in the file. In this case, we have used a name that also indicates the coordinate system that is used by the starting point coordinates in the file.
The moment we load the traverse file, the system automatically shows a blue line preview of how the placeholder object will be modified if we choose to commit the changes. Manifold has automatically parsed the traverse file and has loaded all the straight line segments from the traverse file as well as the three curves specified by the traverse.
We can click the coordinate list format picker
button to switch between showing the coordinates that define the previewed
line in either XY/XYZ format or in traverse format. The illustration
above shows default XY/XYZ format.
We press Update Record to commit the changes.
The placeholder line is replaced with the new line brought in from the traverse file. We Alt-click somewhere outside the line to un-pick it, so it will be seen with normal style and not as a picked object.
The new parcel line appears, using the highly visible style we specified for lines in the Parcel layer.
We import a scanned image of the plat map, georeference it using the Register pane, and then place it as a layer with 50% opacity above the Parcel drawing, rotated and scaled to approximately the same dimensions as the parcel. We can see how the instructions in the traverse file, which were created based on the surveyor's notes in the plat map, have resulted in the parcel line that was created from the traverse.
Zoomed out as in the illustrations above the traverse created from the file seems to be a closed traverse, in that the end point of the final segment precisely coincides with the starting point of the first segment.
However, if we zoom in to the starting point at the Northwest corner, we see that the final segment does not end precisely on the starting point:
The traverse commands, therefore, are in error, since the traverse is supposed to represent the closed boundary of a parcel, with no undershoots, overshoots, or gaps between the final segment and the initial segment. The key question in such cases is what error or errors have caused the problem. Is the problem caused by errors of direction and/or distance in the traverse command for final segment only, with all other segments having exactly correct traverse commands? Is the problem caused by errors in traverse commands for other segments?
A simple way to close the traverse is to pick the line for editing, and then, with snap turned on, to move the final coordinate for the final segment directly onto the coordinate for the starting point. That will adjust the traverse command for the final segment only, basically acting on a belief that the commands for all other segments are precisely accurate.
The reality in real life surveying, however, is that when traverses do not close the error usually is not just in the final segment, but is either in some other segment or, more frequently, the result of slight inaccuracies measuring angles and distances for all the segments, and thus more or less evenly distributed throughout all the traverse commands for all segments. A useful approach used in practical surveying is to adjust all segments slightly in an evenly distributed way, so the result of all the slight adjustments is to close the traverse, with the end of the final segment coinciding precisely with the starting point.
There are many possible algorithms that can be (and have been) used to "evenly" distribute changes between all segments of a traverse to close the traverse. One of the most popular and widely used algorithms is called the compass rule, and is also known as the Bowditch rule. See the discussion on this web page. The compass rule is implemented automatically in Manifold's End Current Branch + Close Gap editing command, which is available when editing an object in insert mode.
The End Current Branch + Close Gap editing command is simple to apply if we are creating a traverse by creating a new line or area as shown in the Traverses topic, entering the traverse command for each segment. When we enter the traverse command for the final segment, if we switch to Show Coordinates mode in the Info pane Coordinates tab and the final coordinate is not the same as the starting coordinate, we know the traverse does not close. In that case, we can simply right-click anywhere in the map window and choose End Current Branch + Close Gap from the context menu and the traverse segments will be adjusted to close the traverse.
However, if we have an existing traverse and we alt-click the line, the object will not be in insert mode and we will not see an End Current Branch + Close Gap choice in the context menu. Manifold will add that in a future build, but for now there is a workaround that allows us to put the traverse into insert mode in a way that provides that choice in the context menu.
What follows will seem complicated for beginners because every step is shown with explanatory text. An experienced Manifold operator can do the sequence below in about fifteen seconds.
Alt-click the traverse line to pick it, and then press the Coordinates tab in the Info pane. The illustration above shows panes docked to the left side of the desktop.
Choose Show
Traverse in the coordinate mode button, and then right-click on
the last traverse command.
Choose Copy from the context menu. That copies the last traverse command to the Windows clipboard. We will need it later.
Ctrl-click the last traverse command to select it and then delete it by pressing the red X Delete command button in the Info pane toolbar.
In the map window, right-click the last coordinate handle.
Choose Continue Branch from the context menu.
The traverse line is now in insert coordinates mode. Click anywhere to add a coordinate.
A small edit handle appears where we clicked, and a new traverse command row appears for the new segment. In the Info pane, double-click the new traverse command.
Double-clicking the new traverse command puts it into editing mode. Press Ctrl-A to select all of the command.
Press Ctrl-V to paste, or right-click into the editing box and choose Paste. That will paste the traverse command that we previously copied.
Press Enter to accept the edit. We now have recreated the last traverse command, with the traverse line still in insert coordinates mode.
We can now right-click anywhere in the map to get the context menu we want.
In the context menu we choose the End Current Branch + Close Gap command.
The entire traverse is immediately adjusted using the compass rule. To apply the changes made, we can press the Update Record button in the Info pane.
Blue color used in editing - Objects that are picked for editing, as well as paths drawn by the measurement tool and in editing, have their coordinate edit handles and boundaries shown using the same blue color used for previews and for provisional edits in other settings. If desired, we can change the preview and provisional color used by Manifold in the Tools - Options dialog. This allows us to use a color different than blue color in cases where a visual display already uses very much blue color or to provide a more discernible color in case of color blindness.
Initially unknown parcel locations - In this example we zoomed into the region where we knew the parcel would be created. Suppose we do not know where the parcel will be created? That is easy to manage. We simply create a new line as a placeholder anywhere at all. Next, we Alt-click the line and in the Coordinates tab we load the traverse file, replacing the placeholder line, and we update the object. The new object almost certainly will not be in view, but we can bring it into view by Ctrl-clicking the Parcel tab to zoom to fit the contents of the Parcel layer. Done.
Starting point - Where did the starting point coordinate numbers in the traverse file come from? Whoever created the traverse file knows the answer to that question. If they started with hand written surveyor's notes, they might have started with a hand written file that included the starting point coordinate numbers. More frequently, a modern GIS operator might have created the file by picking one of the corners of the plat map and proceeding to write the traverse file based on the sequence of surveyor's notes from that starting point. The coordinates of the starting point could be determined from an already-digitized neighboring parcel that shares the same point, by measuring the location of the point on a paper map, by measuring the location from carefully georegistered aerial photos showing the parcel, or by measuring the location using high precision GPS equipment in the field.
Not the only format - This particular example loads an object from a traverse file in Esri traverse file format. As discussed in the Info Pane: Coordinates topic, we can save objects to and load objects from Manifold coordinate format as well.
Thank you! - This topic uses images and files generously contributed as a test case by intrepid Manifold user dchall8 on the georeference.org user forum.
Create Parcels from Traverse Files - Manifold's ability to handle curves and sophisticated geometry makes it easy to create parcels from plat maps and survey documents that describe traverses, using industry-standard Esri traverse files. Also called "metes and bounds" descriptions, traverses are widely used in surveying in the US to define parcels and lines by describing a sequence of directions, distances and curves from a starting point. Manifold automatically handles both tangent and non-tangent curves and the full variety of options used to specify angles, distances and curves. This video shows how it's easy to create a parcel from a traverse file. This works in the free Viewer, too, so anyone can visualize a traverse. Release 9 and Viewer can create Esri-standard traverse files as well!