Same parameters and data input into the habitat quality module of Invest model, but their results are different?

[JCJC]

Habitat quality and habitat degradation are different, so what’s going on?

[jdouglass]

Normally we would expect that running the same version of the InVEST Workbench on the same operating system on two different computers should produce outputs that are numerically equal within a reasonable tolerance (usually around 1e-7). Files might not be bit-for-bit equal, though.

To help us understand what’s going on:

• How different are the outputs between the two computers?
• Are these two computers both running the same operating system?
• Are these two computers both running the same version of InVEST?

[JCJC]

Thanks for your answer. I found the problem that they are different of version. One version is 3.11, the other is 3.13, and 3.11 has a maximum degradation index of 0.262381, while 3.13 has a maximum degradation index of 0.476751, but I don’t know why there is such a big difference.

[dcdenu4]

Hi @JCJC,

Thanks for your follow up. This difference is due to a change we made between versions with the Habitat Quality model. From our changelog:

The model now uses an euclidean distance implementation for decaying threat rasters both linearly and exponentially. Since InVEST 3.3.0 a convolution implementation has been used, which reflected how the density of a threat or surrounding threat pixels could have an even greater, cumulative impact and degradation over space. However, this was never properly documented in the User’s Guide and is not the approach taken in the publication. The convolution implementation also produced degradation and quality outputs that were difficult to interpret.

There should be a noticeable runtime improvement from calculating euclidean distances vs convolutions.

We believe that the 3.13.0 version of the model does a better job representing degradation and recommend using that over previous versions.

Hope this helps!

Doug