I was working on a scene and couldn't get the ground (not the default poser ground prop) shadow to render nicely. So I tried poser clothplane in place of the ground to see how the shadow renders and it came out exactly how I wanted it to. So after trying to figure out what could be the difference, only thing that I could find wrong with the ground prop is that the ploygon is rather large compared to the clothplane. So I increased the scale of the clothplane polygon similar to the size of the ground polygon and the shadow rendered poorly just like the ground.

Sorry if I am asking something basic here but is this right? Does shadow render differently according to the size of the polygon? I understand that shadow would cast differently, obviously, if the polygon is shaped, but if it's just a flat surface than how could it have any affect on shadow?

this may be the shadowcam effect, i.e. if one vastly increases the scale of an object in the scene, the shadowcam may "zoom out" to encompass it. hence the poor shadow resolution that results from such an operation, as it's analogous to dramatically decreasing shadowmap size.

Hmmm, that's very interesting.
I did a quick test with clothplane at its default size along with grounp prop visible and shadow rendered poorly on both. I just did another render with now ground prop scaled down to 20% from 100% and, guess what, the shadow rendered perfectly!

I am curious, how those shadowcam determine this "zoom out"? The ground prop is originally imported from obj file and, even though polygons are huge, it is in default scale of 100%. Also, how those this zooming out effect shadows on other objects? In another word, if I mess around with the values in shadowcam to adjust the shadow on the ground, would it also effect other objects?

Thanks for the tip btw.

I did a search on shadowmap and I think I now know what you mean by "zoom out". Would increasing the shadowmap size for the light fix this? I increased the map for all the lights and test rendering right now but it's processing really slowly. Crossing my fingers that it comes out alright.

no, chin - one should "zoom in" on the shadowcam, rather than increase map size. the former has a similar effect to the latter in terms of render quality, but "zooming in" speeds things up considerably.

Thanks so much for your help!!!
Zooming into ~20% did the trick. I now got a really good looking shadow on the ground like it's suppose to.

OTH, as for the render with shadowmap size increased, once it finally rendered, the shadow came out really sharp and beautifully but off the figure like before. I am guessing that zooming in would fix that also but what exactly does increasing the shadomap do? Is it to increase the quality of the shadow?

Thanks again.

increasing shadowmap size from 256 to 2048 represents an increase in resolution (and virtual RAM wastage) of 64X, but zooming out on the shadowcam may vitiate that increased resolution, in the same way that doing an extreme close-up render of a 2048X2048 body texture will show pixellation and rough edges. check the manual under shadow parameters, although I see Anthony forgot to write a detailed discussion of shadowcams - no surprises there

Hehe, yes good ol' manual :)
I am really not gonna slam the manual here, but let's just say that I forgot all about the manual once I found this forum. :)

But, really, I think I should pull out the manual and get whatever info I can get on this because these are some interesting stuff here. Funny thing is, whenever I think I learned alot about Poser, it always throws something new at me making me feel like I am barely scratching the surface. So much to learn...