AC Report vs RTAC Dialog

This note covers a difference between ISCWSA Rev 4 and Rev 5 error models that can cause confusion for users.


There have been instances where differences between Well Seeker Pros anti-collision report and the RTAC (real time anti-collision) dialog have been noted for the calculated error ellipse and subsequently the separation factor. This only occurs when an ISCWSA Rev 5 IPM is utilized and the course length between the last two rows in the survey grid is in excess of 100ft.

Both the anti-collision report and RTAC dialog results are correct in their own right, but require some explanation for the user to understand this.


ISCWSA Rev 5 IPMs incorporate three important new error terms compared to ISCWSA Rev 4 and prior IPMs. These are:

mdfac, xcli, xcla

Historically to use an IPM the user was assumed to have a maximum survey interval of 100ft. However, prior to ISCWSA Rev 5 IPMs, there was no significant change in the error ellipse calculated if this rule was not followed. The above error terms present in ISCWSA Rev 5 IPMs now takes in to account the distance between survey points and if this is excessively large the error ellipse calculated is significantly increased in size. This then has a large effect on the separation factor calculated

To determine whether an IPM is an ISCWSA Rev 5 IPM the user can find the IPM files in the C:\Users\Username\AppData\Roaming\Well Seeker Pro\IPM folder and open individual .ipm files using Notepad. The user can then check for the above terms and if present will confirm a Rev 5 IPM

Alternatively the user can do this via the Survey Tool Editor within Well Seeker Pro

Anti-collision report: Only runs the separation factor calculations based upon the data present in the selected survey/actual wellbore/plan listing.

RTAC dialog: This has been designed specifically for anti-collision scanning whilst drilling and has been optimized to run from a survey and to include projections over large course lengths. As a result, any surveys / projections with a course length in excess of 100ft are interpolated behind the scenes.


Be aware of the tool that you are using. Anti-collision reports should be used for survey listings and plans, but will calculate significantly larger error ellipses and smaller separation factors if large course lengths are present when an ISCWSA Rev 5 IPM is used.

RTAC dialog results will display assuming you are surveying the wellbore correctly, giving realistic error ellipse and separation factor results, even if large course lengths are present between rows in the survey listing when an ISCWSA Rev 5 IPM is used.

If using ISCWSA Rev 4 or previous IPMs then there will be no difference between the anti-collision report and the RTAC dialog.