Overview
The aim of this app is to demonstrate the relationship between geographic
location and solar position throughout the year. You can use the map to drag the location around
and interactively see how the Sun-path diagram and shadow projections change. You can also directly
relate the 3D Sun-path and day-length, as well as a range of different 2D Sun-path projections.
Background
This started out as an experiment to see just how responsive I could make
the generation and display of 3D Sun-path diagrams and shadow projections using JavaScript and WebGL.
I'm actually quite stunned as, even before any optimisation whatsoever, I found that I could build and
rebuild the entire Sun-path mesh on every change in pretty well real time. Sure this was on an i7
processor, but it meant that the core technologies were not going to be the kind of bottleneck
that I thought they'd be.
As it turned out, there was scope for some pretty fundamental optimisations, so now it's even quick
enough on an iPad as well as most of my old Android tablets.
SVG and WebGL
The marriage of WebGL for 3D visualisation and SVG for 2D data presentation also turns out to be
a pretty happy one. The core ideas when working in both are actually pretty similar - building up
a set of visual components that are cached and rendered separately (OpenGL vertex buffer objects and
SVG elements respectively). Any complex calculations in Javascript need only be done once to build
up each visual component, or to rebuild if it physically changes. The actual rendering of that cached
element is then done by a much faster lower-level process (OpenGL/GPU and the SVG engine respectively).
Optimsation Potential
Thus, for the kinds of animated 2D charts I need, SVG seems to have much more optimisation potential
than using a HTML5 canvas element. As the canvas element is pixel-based, any content change usually
requires a full redraw of all chart components, each being re-described and/or re-generated in
your own Javascript code. If any components require complex calculation or involve detailed curves,
you have to devise your own caching system as this all has to be redone for every redraw.
With SVG charts, you only need to re-describe and/or re-generate those components that actually
change on each redraw. All other previously defined components are automatically re-rendered by
the SVG engine, which is a core part of the browser itself (running as native code) so is
significantly faster than working in Javascript.
Thus, the key to fast animations is to offload as much work as possible onto the SVG engine, or
even the browser rendering engine. This can be done by, for example, transforming components instead
of regenerating them, using CSS3 animations and transitions, interpolating between pre-built elements
instead of regenerating new elements each time, etc. For me, this is the really fun bit as you often
have to completely rethink how to do things before you finally get that vital Eureka moment.
© Dr. Andrew J. Marsh, 2014.
View Manipulation
You can interactively adjust the 3D view of the model using a mouse,
pen or stylus, or by touch on a tablet or phone.
You can also use the items in the 3D View Settings popup.
- Rotation:
- Drag with the left/right button or a single finger,
or use the arrow keys.
- Panning:
- Drag with the middle button or two/three fingers,
or use the A and D keys.
- Zooming:
- Use the scroll wheel or pinch with two fingers,
or use the W and S keys.
NOTE: You can use the Shift and Ctrl/Meta keys to adjust the increment
of each scroll event or key press.
Keyboard Modifiers
The Shift and Ctrl/Meta keys are used pretty extensively
to modify interactive data entry. This applies to all increment buttons, scroll wheel motion,
slider controls and input elements.
- Shift Key:
- Increases input to larger values, usually by ten times or significantly larger increments
such as 1 month for dates and 1 hour for times.
- Ctrl or Meta Key:
- Decreases input to smaller values, usually by one tenth or the smallest reasonable increment
such as 1 day for dates or 1 minute for times.
NOTE: You can use the scroll wheel to edit a data value when hovering over any slider,
numeric input or even table rows that indicate their editibility.
