Hello. I’m using the InVEST HQ model and have a question.
Many papers say that the default value of the Half-Saturation Constant is 0.5.
However, in the user guide, the default value is 0.05. (photo 02)
So it’s very confusing…
I looked at the history page to see if it had changed, and it says it was changed from 0.5 to 0.1. (photo 01)
But the user guide is still at 0.05.
I’m wondering if it’s a typo in the user guide or if it really changed.
Does anyone know???
Hi @Ahmee,
Thanks for your post and welcome to the NatCap Forum community!
The default half saturation value that is used for the provided sample data is indeed 0.05, as mentioned in the User’s Guide. The change log entry you refer to is worded a bit funny, but is saying that the value was changed from 0.1 to 0.05. So that lines up as well.
Indeed the paper did use a 0.5 half saturation value as the default, but we’ve updated it over the years as our sample data has changed. As mentioned in the User’s Guide it really should be set by the user:
The default value is 0.05. In general, you want to set [the half saturation value] to half of the highest grid cell degradation value on the landscape. To perform this model calibration you will have to the run the model once to find the highest degradation value and set [the half saturation value] for your landscape. For example, if a preliminary run of the model generates a degradation map where the highest grid-cell degradation level is 1 then setting [the half saturation value] at 0.5 will produce habitat quality maps with the greatest variation on the 0 to 1 scale (this helps with visual representation of heterogeneity in quality across the landscape).
I hope this helps clear things up!
Doug
Wow, thank you so much!
I must have been misunderstanding something.
I appreciate the reply. Have a great day! 
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