Welcome Tonima!
Yes that difference is not very well communicated. The latter is only really in place to permit masking when performing the TW-FC method. Basically:
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“
scalar_map” samples values from an associated image and (in conjunction with the track-wise statistic) provides each streamline with a scalar value reflecting the image values underlying the streamline trajectory; -
“
scalar_map_count” instead assigns to each streamline either a 1 or a 0 depending on whether or not a non-zero value is measured from that image anywhere along the streamline, and can therefore be used to generate an image reflecting the “count” of streamlines that actually contribute to an image generated using the former.
However I’ve never been happy with this interface in the slightest. In retrospect the latter should have instead been achieved as a track-wise statistic within the TWI framework. Longer-term I’m intending on changing the relevant parts of the tckmap interface more drastically; but hopefully that at least explains the options that are there now.
Cheers
Rob