QUESTION:

I am looking to calculate the shading percentage of a particular shading system. I clicked on the window, chose Calculate » Sun-path Diagram and am displaying tabulated daily solar data. The percentages I get are written as [-25(%)]. Is it safe to assume that this means 25% exposed ? (compared to when it state 100% meaning no sun ?)

ANSWER:

[-25(%)] on the tabulated data, means that the surface is 25% shaded, with the -ve meaning that the sun is behind the face, i.e. opposite side.

You should only get these -ve values if you have selected the Check Both Sides of Surface option in the Calculate Shading dialog box.

This behind/in-front stuff is directly related to the surface normal of the chosen object (i.e. which way the object is pointing) and where the sun is in relation to this.

If you display surface normals for your model, the direction the normal is pointing is considered the "outside" or +ve direction, whilst the -ve is obviously the other side to this -- then depending on whish side the sun is in relation to this will mean you might end up with -ve data values.