Miscalculation of dht2 CoveredArea for point transects with left truncation

[Tristen Brush]

Hi Eric, I just wanted to flag for you that I believe the 'dht2' function in Distance 2.0.1 for R is ignoring the left truncation distance in calculating CoveredArea for point transects. I have truncation at 1m and 15m, and my effort is 332414114. By my calculations, my covered area should be pi * (15^2 - 1^2) * effort * km conversion = 233925.3814 sqkm. The dht2 output, however, is giving me pi * 15^2 * effort * km conversion = 234969.7 sqkm. I don't know that this would greatly affect my estimate, but I think it would be more severe when the left truncation distance is larger.

Can you suggest any workaround to deal with this manually for now? Some of my datasets are left-truncated at 2 and 3 m, so I'd like to see how/if my estimates change.

Thanks as always!

Tristen

[Eric Rexstad]

Tristen

Nice to hear from you again. Good of you to be closely checking your calculations.

When developing code to deal with CTDS, we had extensive discussions regarding left truncation. I believe the implementation of left truncation is correct, given the correspondence of density estimates from Howe's duiker data using both the Distance R package and the DistWin software.

Have a look through the comments associated with this pair of Github issues created at the time of software development of the Distance package:

https://github.com/DistanceDevelopment/Distance/issues/135

https://github.com/DistanceDevelopment/Distance/issues/64#issuecomment-656803831

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From: distance...@googlegroups.com <distance...@googlegroups.com> on behalf of Tristen Brush <teb...@gmail.com>
Sent: 02 February 2026 20:19
To: distance-sampling <distance...@googlegroups.com>
Subject: [distance-sampling] Miscalculation of dht2 CoveredArea for point transects with left truncation

 

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