The parcel fabric uses the DynAdjust least-squares adjustment engine, which is a least-squares application that adjusts coordinates of both small and large geodetic networks. DynAdjust uses a phased adjustment approach in which large networks are adjusted in sequential blocks. The DynAdjust engine can scale to adjust small engineering surveys to large, national geodetic networks.
Some of the capabilities of the DynAdjust least-squares adjustment engine include the following:
- Adjustment of coordinates in three dimensions (x,y,z)
- Support of multiple measurement types, for example, horizontal angles and geodetic azimuths
- Constrained adjustments (adjustments using known, weighted control points)
- Minimally constrained or free network adjustments
- Estimation of precision of adjusted coordinates
- Statistical analyses of adjustment results
Learn more about the DynAdjust least-squares adjustment engine
Parcel fabric dimension processing in the DynAdjust engine
Use the Analyze Parcels By Least Squares Adjustment tool to run a least-squares adjustment on parcels. In a least-squares adjustment, parcel data is input to the DynAdjust least-squares engine, adjusted using least-squares adjustment, and output to adjustment analysis layers. If the results in the adjustment analysis layers are acceptable, you can run the Apply Parcel Least Squares Adjustment tool to apply the adjustment results to the parcel fabric.
Parcel lines and connection lines
Parcel line and connection line dimensions are typically input as distances and direction sets to the DynAdjust least-squares engine. Lines that have been configured as geodetic lines are input to the engine as ellipsoid arc distances and geodetic azimuths.
A direction set is composed of an origin point (the from point), a backsight line (reference line), and one or more foresight lines.
Distances and direction sets are processed in the least-squares adjustment as follows:
- The angles formed by the direction set are the measurements that are input to the least-squares engine. The angles are derived from the COGO direction value of the backsight line and each of the foresight lines.
- In the image above, point 3762 is the origin point of the direction set. The backsight or reference direction is the line from point 3762 to point 3186. The foresight direction is the line from point 3762 to 3763.
- In the least-squares adjustment, the angles are adjusted and applied to the foresight directions to obtain adjusted foresight directions for the lines. The least-squares adjustment returns adjusted directions and distances for the foresight lines of the direction set.
- If the directions on the backsight or foresight lines are in the opposite direction, they are reversed in the direction set.
- When a point in the parcel fabric has multiple lines connecting to it and those lines belong to separate (adjacent or overlapping) records, a separate direction set is formed for each set of lines in each record. Grouping the direction sets' lines by the record they belong to accounts for the possibility of different bases of bearings (rotations) being used for different records.
- Least-squares adjustment inputs and results are stored in the AdjustmentLines feature class as follows:
- The origin point of a direction set is stored in the Point 1 Name field. The end point of the backsight line is stored in the Point 2 Name field. The end point of the foresight line is stored in the Point 3 Name field.
- For distances, the from point is stored in the Point 1 Name field and the to point is stored in the Point 2 Name field. There will be a Null value in the Point 3 Name field.
- The direction set angle or distance of the foresight line is stored in the Measurement field. The Measurement Type field uses a subtype that indicates whether the measurement is an angle or a distance.
- The adjusted COGO direction or adjusted distance of the foresight line is stored in the Adjusted Measurement field.
- The difference between the adjusted foresight dimension and the original dimension is stored in the Measurement Correction field.