I think i'm having a blond week, i have found that when I am using third party ground props or ground figures, I very often don't  get any ground shadows in final renders, often even with the ground shadows option turned on in the preview window I get no shadow showing in preview either. Am I doing something wrong and if so what?

just to add, it doesnt happen on all ground  figures and props.........

Without a screen shot to know for sure, if you don't have the ground mesh showing, you won't have any shadow.  Check the hiearchy menu and ensure that the ground plane is checked.  Jan

Stated another way, if the vendor's ground texture is above the poser ground plane, you won't get shadows. Make the poser ground a shadow catcher and position it just ABOVE the vendor groundplane.

thanks for the advice, by positioning the poser ground above, i guess you mean dropping the vendor ground plane on the Y co-ords, coz the poser ground plane wont budge on the y axis

Correct

I know this question might be a bit insulting (for which I apologise in advance), but lighting? Ray-trace? How many lights? Shadows enabled?

Quite right, Robyn... I tend to render everything raytraced by default, shadows emabled if I want a shadow. I forget to mention that sometimes.

As to number of lights, etc, I don't see where that matters.

If you have some of those legacy lights (where they're like 12 or 15) there will be too many lights all over the place for any one of them to actually cast an effective shadow, depending on how they're positioned. I tend to use IDL now in all my images and 1 light for all outdoors scenes. And a sky-dome.

Indoor, I will have multiple lights, but one will be stronger than the rest if I want distinct shadows. I'm just in process of setting up an ICU scene where lighting is more diffuse.

Mind you: IDL is not perfect. I've an image that - I think - illustrates that schmutz Bagginsbill was referring to in that VRay thread by MistyLaraPrincess:

Where her body meets the couch the shadows are really meh.

IDL quality was perhaps a bit low: 7. Pixel samples: 9. Post filter size: 2 (sinc). and raytraced shadow samples for the only light (inf, map-size 1024, white, 220%, RT SBR: 6, SMB: .3) was 60. Still too low? Oh, no AO. Dunno if this was a good idea or no, but I did add the skydome as a light-source (diffuse_value:0, ambient_value: 1).

Well, back to the main shadows: they seem okay. Just not the ones at the skin/couch intersection.

Quote - if you don't have the ground mesh showing, you won't have any shadow.

The above statement is not correct. Any surface that you can see should be capable of accepting a shadow.

Except, they often don't. I've never been able to figure out why. Do you know, Les?

Note that my last post relates to "real" shadows. "Ground Shadows" are just a positioning Guide (like Horizon Line), and will not show in a rendered image. For Ground Shadows, the GROUND does need to be above any floor object.

Quote - Except, they often don't. I've never been able to figure out why. Do you know, Les?

No I can't give you a definitive answer, but consider this. A floor is just a wall rotated 90 degrees. So if a wall will show a shadow, if you parent all the lights to the wall and parent the all the objects casting shadows to the wall, than rotate the wall 90 degrees so that it becomes a floor, logic would seem to dictate that it will still have exactly the same shadows. Now I must admit that I am working entirely from logic here. I have not actually done the experiments to prove it, but I would be very surprised if such an experiment failed and Poser proved to be anisotropic in this respect.

On the other hand, it seems to me that Poser has no great respect for logic.

[quoteOn the other hand, it seems to me that Poser has no great respect for logic.

ROFL. This has been my experience as well.

Nornally, things work as you describe, however... From time to time I find an environment piece that will not receive shadows. In those cases, the only way I have ever been able to get the shadows has been to either: a) lower the ground of the piece below the poser ground plane or b) place a one-sided square under the characters just above the enviroment plane and set it as a shadow catcher.

I have never been able to find a rhyme or reason for this behavior... it seems totally random. The next time I catch one doing it, I'll post and start a thread.

Check the Mat Room.  If you have an ambient channel active on that ground object, you will never get an effective shadow on it.  I reiterate, check shader settings in the Mat Room.

Yes, what hborre said is one likely cause. Environment props often have the Diffuse_Value and Specular_Value set to zero (or using a black color has the same effect), then the texture is plugged into the either the Ambient_Color or the Alternate_Diffuse. This has the effect of isolating the object and any texture it uses from the scene lighting.

Another cause is, as RobynsVeil pointed out, light pollution from too many lights, or an inappropriate IBL set up can wash out the shadows.

"How many lights? Shadows enabled?"

Be aware that with multiple lights only one should have cast shadow enabled, and also be aware that the shadow cast by that light can be "nutralised" if other lights are shining into the shadowed area cast by that light.

I'm pretty much tired of trying to get several lights correctly set up and now generally just use one light with IDL. Call me lazy.

Quote - I'm pretty much tired of trying to get several lights correctly set up and now generally just use one light with IDL. Call me lazy.

Same here!

Usually when I have a shadow that won't show up it's because my light that casts shadows isn't pointed in the direction I think it's pointed in....