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.
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:
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, 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.
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.
How did we place the scanned image? - In the last illustration a scanned image of the plat map was imported and then positioned, scaled and rotated to approximately overlay the parcel. Current builds require significant manual tinkering to scale, position, and rotate such an image layer, but future builds will make that process very easy.
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!
Info Pane: Coordinates