Shadow mapping issue - graphics

I've implemented shadow mapping to generate shadows on a terrain.
I render the scene (or the objects that cast shadows) from the light's perspective and then generate a depth map to be sampled during the second render pass (as all the tutorials on the web explain).
It seemed to work fine but then I noticed that objects on a hill cast more than one shadow:
I think that's the correct behaviour since I don't render the terrain during depth map generation (the small quad on top right shows the depth buffer during the first render pass), so more terrain fragments look like they're behind the object from the light's point of view.
No tutorial on shadow mapping seems to mention this issue though.
Am I missing something or this shadow generation technique is very basic and issues like this one are likely to occur?
EDIT
here's my rendering code:
// in my Render() method:
mShadowRenderer.SetLight(*mLights[0]);
mShadowRenderer.Render();
RenderSkyBox();
RenderEntities();
RenderGeometryTerrain(mTerrains[0],
mShadowRenderer.GetLightViewProjectionMatrix());
shadowRenderer is a class that is in charge of rendering to an off-screen buffer and to return a depth map as a shader resource view. The depth map is added to the terrain when I call the render method so it can be sampled in the terrai pixel shader to generate shadows.


Also, the terrain needs to be rendered to the shadow map/dep map

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I manage the map through image views placed side by side to form a grid. How could I implement map zoom-in and zoom-out by loading all frames and elements without them getting distorted?

Without knowing any details about your rendering method I would suggest to use a Camera. The OrthographicCamera class provides a zoom attribute whereas the PerspectiveCamera can "zoom" via altering its position.z.

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As I understand it, if I create a vtk render window, then I can add different renderers to it and for each renderer renders from a different perspective. No to actually render the scene I use the vtk render window method render() to render all renderers in parallel. Now there is a vtk render window method called GetZbufferData which apparently returns an array containing the zbuffer. So my question is, to which renderer does this zbuffer correspond to?
Thanks for any clarification.

If you have all renderers in the same window, then they will share the same framebuffer, so also the same z-buffer. So a simple answer to your question is "to all of them". To get the individual z-values, it depends on what you are exactly doing with the renderers.
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double x1 = ren1->GetViewport()[0] * (renWin->GetSize()[0] - 1);
double y1 = ren1->GetViewport()[1] * (renWin->GetSize()[1] - 1);
double x2 = ren1->GetViewport()[2] * (renWin->GetSize()[0] - 1);
double y2 = ren1->GetViewport()[3] * (renWin->GetSize()[1] - 1);
float *ren1Z = renWin->GetZbufferData(
static_cast<int>(x1),static_cast<int>(y1),static_cast<int>(x2),
static_cast<int>(y2));
If you have the same viewport, it would be more complicated. You can have a renderwindow with multiple "layers", by setting vtkRenderWindow::SetNumberOfLayers(int) and then you can assign each renderer to a different layer (vtkRenderer::SetLayer(0-based layer index)). The window then renders from layer 0 to the last layer over each other. If you are interested in getting only one specific renderer's z-data, you should get it if you have it render in the last layer. However, I am not sure if the z-buffer is cleaned in between individual renderer's renders, I would actually bet on that it is not, so you might also get some inconsistent mess.

I would like to complement tomj answer:
Any of the vtkRenderWindow::GetZbufferData() methods query the framebuffer for Z-values, which is contained in the vtkRenderWindow, but there is a slight remark:
You need to set this in your renderers: vtkRenderer::PreserveDepthBufferOn(). This is because as the documentation says:
"By default, the depth buffer is reset for each renderer.
If this flag is true, this renderer will use the existing depth buffer for its rendering."
So, that bring us to the vtkRenderers. There is a layering of vtkRenderers, which tells which "chain" or "precedence order" to make the drawing. Check the method vtkRenderer::SetLayer().
So, you first need to set up your layered vtkRenderers, attach them to the vtkRenderWindow, and then set up correctly if you want to preserve some depth buffers or not.
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I am attempting to rotate an MKMapView using MapKit.
I can display a map and rotate it, however not very efficiently. I create an MKMapView larger than the view and rotate it using CGAffineTransformMakeRotation, so the the grey areas behind the view are not visible. Although I have clip subviews checked in Interface Builder, I still have the feeling this is not the correct implementation.
This method does allow me to rotate any annotations displayed as MKPinAnnotationView conforms to the CGAffineTransformMakeRotation function, but I come into problems when trying to add an overlay to the map.
I can place an overlay on using the boundingMapRect property in the class declaration but the image remains unrotated on the display. Is there a way to achieve this? Or alternatively should I be rotating the MKMapView and annotations in a different method?
Thanks in advance for any advice or information.

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