The cadastral adjustment applies weighting to all bearings and distances in the data. There are six levels of accuracy as follows:
|Accuracy ||SD Bearings(Secs) ||SD Distances ||PPM (Metres)|
|1 ||5" ||0.001 ||5|
|2 ||30" ||0.010 ||25|
|3 ||60" ||0.020 ||50|
|4 ||120" ||0.050 ||125|
|5 ||300" ||0.200 ||125|
|6 ||3600" ||1.000 ||1000|
|7 ||unknown accuracy ||excluded from adjustment|
Initial values are set according to the date as follows:
|Accuracy ||Date Range|
|2 ||After 1980|
|3 ||1908 - 1980|
|4 ||1881 - 1907|
|5 ||Before 1881|
Line type 995 (usually used for a direct connection to a control point.) is held at an accuracy one beeter than its Parcel accuracy.
Processing Old Files
As there was no accuracy variable available in the DOS version of the software, the lot type and line type was used to override the default accuracy. When these files are read in to GeoCadastre, the old rules for setting accuracies are used to explicitly set each parcel and line accuracy, and the lot and line types are stripped of the extra data.
The old rules were as follows:
Compiled plans were flagged by setting their lot type to be 16 to force them into accuracy 5, or to lot type 17 for accuracy 6.
The default lot accuracy could also be overridden by adding a multiple of 1000 to the lot type as follows:
|Accuracy ||Date Range ||Lot Type ||Line Type|
|1 ||N/A ||2000 - 2999 ||995|
|2 ||After 1980 ||3000 - 3999 ||N/A|
|3 ||1908 - 1980 ||4000 - 4999 ||N/A|
|4 ||1881 - 1907 ||5000 - 5999 ||N/A|
|5 ||Before 1881 ||6000 - 6999 ||N/A|
|6 ||N/A ||8000 - 8999 ||N/A|
By adding the appropriate value to the original lot type the accuracy indicator could be
included and the original lot type maintained.
For example a lot coded 2997 would be an unclosed traverse of accuracy 1.
To cater for compiled plans whose dimensions may be based on a much older survey and for
partially compiled plans where only some lines were surveyed, 800 was added to the line type
to indicate that its accuracy should adopt the accuracy according to the date of the plan.
Old jobs are now converted as they are read in according to the following rules:
- Lot types 1000 - 1999 were for "historical" surveys. These are now tagged as “historical” and 1000 subtracted from the lot type.
- Lot types 7000 - 7999 were lots to be excluded from the adjustment. These are now set to accuracy 7 and 7000 subtracted from the lot type
- Lot types 8000 - 8999 were for very old lots of poor accuracy.These are now set to accuracy 6 and 8000 subtracted from the lot type.
- Lot type 997 type was for an unclosed parcel. These are flagged as "Unclosed" and the lot type set to 0.