Created Defining custom perspectives (markdown)

Defining-custom-perspectives.md

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+If the standard, predefined perspectives are not suitable for a user's needs, custom perspectives can be defined.  With custom perspectives, a user is free to utilize the full flexibility and capabilities of the rendering engine.
+
+At present, only one class of perspective is supported: the IsoHDPerspective class.  This class defines an isometric viewpoint, with full control of the direction of view, angle of view, and scale of view.  The definition of a perspective is structured as follows:
+
+    perspectives:
+      - class: org.dynmap.hdmap.IsoHDPerspective
+        name: my_custom_perspective
+        azimuth: 124
+        inclination: 55
+        scale: 16
+
+The required parameters for the isometric perspectives include the following:
+
+- _name_ : the unique name for the perspective.  If a custom perspective has the same name as an existing standard perspective, it will replace it.
+
+- _azimuth_ : the angle, in degrees clockwise from north, of the viewpoint for the map : 0 = north, 90 = east, 180 = south, 270 = west.  Any angle value is allowed.
+
+- _inclination_ : the angle, in degrees below horizontal, of the viewpoint for the map: 90 = top view, 0 = horizontal (not allowed).  Permitted values are any value from 20 to 90 degrees.
+
+- _scale_ : the scale or resolution used for rendering the scene, in pixels per block edge.  Values from 1 to 64 are supported, although 64 would correspond to a HUGE map - 16 yields a very high quality map (corresponding to **hires** in the standard perspectives), 8 yields a good quality map (corresponding to **medres**), and 4 yields a good quality map (corresponding to **lowres**) if a shader other than a texture pack shader is used (cave, biome, colorschemes).
+
+In addition to these core required parameters, additional optional parameters are supported to modify the processing of the perspective:
+
+- _maximumheight_ : if set, this sets a maximum height value (Y coordinate, in the Minecraft map) of blocks to be rendered.  If it is set below 127, all blocks above this height will be invisible - logically slicing the top off of the world as a selected height.  This can be used to show underground views.
+
+- _minimumheight_ : if set, this set a minimum height value (Y coordinate, in the Minecraft map) of the blocks to be rendered. If it is set above 0, all blocks below this height will be invisible - logically slicing the bottom off of the world at a selected height.  This can be used to show underground views.