ArcGIS Events

Spent part of today trying to get an event handler to work in ArcGIS. What I wanted to do was show a form, allow the user to select a button which would hide the form and then allow the user to digitise a line on the map. Double-clicking to end the line would show the form again. The aim is to develop the code in VBA.

So, after a few tries, I came up with the map event handler – but this doesn’t work as the events that you get relate to drawing on the map (see http://esri.com/news/arcuser/1005/files/eventdriven.pdf  – in particular for a list of the events that can be triggered from a map and http://www.esri.com/news/arcuser/0404/files/productivity.pdf for how to use the map event handler).

So the solution seems to be use the Editor event handler.  For some examples of how this works, see:

• http://forums.esri.com/Thread.asp?c=93&f=987&t=140048
• http://support.esri.com/index.cfm?fa=listserve.messageShow&m=45390

What is 3D GIS?

A number of GI vendors tout 3D products around, when in fact they refer to 2.5D – so what is the difference?  Well for 2.5D you can have only one height value (z coordinate) for each x,y coordinate pair.  This allows you to create surfaces (view sheds, line-of-sight) but does not allow you to model true 3D objects, which enclose some space (for example a cube, a building).

So, come on vendors – update your software to handle true 3D or correct your terminology!