Hidden Surface Removal
Hidden Surface Removal (HSR) must be employed to correctly display 3D images of DTMs, 3DMs and strings which have been drawn as colour filled polygons.
If HSR is not used, then the displayed images may not be `correct'. This may not cause you any difficulty as the displaying of the images is much quicker with HSR disabled. If you are only displaying strings as lines then there is no advantage to using HSR and in fact it will slow things down unnecessarily.
Usually, the displayed data in the GRAPHICS module is Polyline data which does not require HSR. In this case the HSR attribute is turned off by default. HSR can easily be turned on at any time by using the function Hide On.
Three different HSR algorithms are available for you to choose from. The method you choose is determined by your computer hardware and the amount of RAM available. You can set the method to be used using the ``hsr algorithm'' option in the defaults.ssi file.
These functions are described below.
HSR Painters
This is the simplest, slowest and least memory intensive HSR method. You should use this method if you have limited memory. The Painters algorithm works in a divide and conquer method by partitioning the area into small rectangular regions and dealing with each region independently. This is why we get the checker board drawing effect when using this method.
To run this function: Choose Customise > Graphics system > Painters method, or...
HSR Software Z-Buffer
This method is much faster then the Painters algorithm, but demands a significant amount of memory.
To run this function: Choose Customise > Graphics system > Software Z buffer, or...
To estimate the amount of memory which will be used by the software z-buffer use the following rule:
MEMORY = XPIXELS * YPIXELS * 5
For example,
MEMORY = 1024 * 768 * 5 = 3 932 160 = 4 Mb
HSR Hardware Z-Buffer
Some high end graphics workstations have HSR implemented in hardware. This is the fastest and most expensive (in dollars) method available. If you choose the hardware z-buffer method and your computer does not support it then it will default to the Painters algorithm.
To run this function: Choose Customise > Graphics system > Hardware Z buffer, or...