May 15, 2009

Optimizing ArcGIS Server

One of my hobbies is experimental sailboat design. And, with anything worth designing the challenges are circular and interconnected; weight, drag, stability, complexity, reliability, speed, performance. Optimization is the usually the balance of these sometimes diametrically apposed factors. If it’s light weight, it may not be reliable, or stable. If it’s stable it may not be fast or light. If it’s fast it may be too complex, unstable and unreliable. The reward in exploring a design is when I find that overlooked and elusive idea that truly can overcome the previous limitations and provide an uncompromised optimization. A solution where I can do something I could not do before; faster, lighter, stronger, simpler and better.

Although most of the things that make published map documents fast and efficient Map Services are likewise good for ArcGIS for AutoCAD, there are a couple things that ArcGIS Server IT managers should consider that are specific to ArcGIS for AutoCAD users. Technically, ArcGIS for AutoCAD uses the ExportMapImage functionality of ArcGIS Server to interact with map services.

Therefore the first order of server business for ArcGIS for AutoCAD is to ensure I have not disabled the ExportMapImage functionality on my map server. Secondly ArcGIS for AutoCAD needs an ArcGIS Server geometry service to project the coordinates of a cached map services if they are different than the coordinate system of the AutoCAD drawing. I do not need a geometry service if both the cached map service and the drawing are in the same coordinate system or when the map service is generated dynamically. ArcGIS for AutoCAD will look for the geometry service on the same server as the map and if it doesn’t find one it looks elsewhere on the internet. If a geometry service is enabled on my map server projecting cached maps for ArcGIS for AutoCAD is faster, if needed.

Better yet, to avoid problems with grainy maps caused by excessive scaling, or the performance hit for re-projecting maps, it’s a good idea to publish my map service in a coordinate system AutoCAD users are likely to be viewing the map. I may have casual mapping users who can view the map service in a geographic coordinate system since they really don’t care what the coordinates are, but generally AutoCAD users are working projected coordinates, like State Plane or UTM. If I expect I will have ArcGIS for AutoCAD users I might consider publishing maps in their commonly used coordinate systems.

Although caching the maps on my map server is a good way to speed things up for most ArcGIS map service viewing applications, it is not necessarily faster for ArcGIS for AutoCAD which still requires that a map image be created, and because of the threshold of discrete scales being set for cashed maps, the quality of the map image could be better if the map service was left to be generated dynamically.

Some of these optimization settings may be at odds with other ArcGIS Server best practices. Both are valid, I might consider creating two different map services, one for ArcGIS for AutoCAD to use and another for general users if I notice performance, or image quality issues due to projections. In most cases the differences are minor, but in combination, and with a large number of users it could become significant.


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