Fabric

Residuals

Residual calculations are used to quickly find any area of disagreement between plan observations. Basically, it is a goodness-of-fit test between two plans.

Basic Use

  1. Select check boxes option on the Fabric Toolbar.
  2. check the subject plan and a reference plan.
  3. click to calculate.
  4. Focus will change to the Tool Results Window.
  5. Perform any desired table sorting on columns.
  6. Select table rows to navigate the map to the point of interest.

Residuals Tool
How to calculate residuals between plans. (CLICK IMAGE TO START DEMO)

Advanced Use - Using Tool Results Window

Once you have calculated residuals, you can re-calculate using only common points in a region of the map or remove selected points from the calculation.

Re-calculate for points in window

  1. Pan and Zoom map to restrict to a region.
  2. click to re-calculate residuals.

Remove selected points and re-calculate

  1. Select the rows in the table you want to remove from the calculation.
  2. click to re-calculate residuals for remaining points.

Note: Most jurisdiction defined residuals calculations distribute error between the points using a Least Squares methodology. This is why re-calculation removing outliers, or for only a section of the plan can be useful.

Details

Key Points:

  1. You can compare residuals between any two plans in the fabric.
  2. These calculations are based on the comparison of how different plans calculate the coordinates of shared points.
  3. PlanTest calculates residuals based on the requirements of the jurisdiction. See your team lead for more information.
  4. There is no residual calculation for the subject plan to the existing coordinates of the fabric. This would only be relevant for a coordinated cadastre, or at least a LSA fabric. Jurisdiction tests may cover this aspect.

Note: Residuals button is enabled only when two plans are in view. The results are shown in the standard Tool Results Window, and as usual, the records of the table are linked to the map. So you can navigate to survey features on the map to further inspect the possible causes of disagreement.

Residual Tool Results Table Columns

Header Description
ID The fabric identification number for the common point.
x Residual in the x coordinates for the common point.
y Residual in the y coordinates for the common point.
B Bearing of line between the two plan's respective coordinates for the point.
D Distance of line between the two plan's respective coordinates for the point.

Note: The D (distance) value is usually the most important. We often sort the D column ascending, then select the top record to go to the area on the map.