Thematic Raster Display in ArcGIS

We do  a lot a high-resolution land cover mapping and due to the number of features we map have really no choice but to store the data in a raster format.  When working with these large rasters in ArcMap we found that artifacts can appear at certain map scales when pyramids are present.  Deleting the pyramids will solve the problem, but this would result in unacceptable display speed for very large raster layers such as the 10GB land cover dataset I use in the example below.  If you click on the image to enlarge it you will notice black pixels (roads) appear to surround the buildings (red).

We found that changing the Display settings to use a Majority resample method noticeably improves the display of thematic raster datasets at larger map scales (we review our 1 meter land cover layers at a scale of 1:2500).  To change the resample setting go into the properties of the layer > Display tab > Resample during display using.

Once we adjust the resample method our land cover layer no longer has the strange artifacts.

Build pyramids and compute statistics in batch

As we all know its much easier display raster datasets if they have both pyramids and statistics.  When working with hundreds or thousands of raster datasets the process of building pyramids and computing statistics can be painfully slow.  In version 2010 of IMAGIINE ERDAS introduced parallel processing.  For every IMAGINE Advantage license four processes can be initiated.  My Dell T7500 supports running 16 simultaneous processes and thus thanks to this and the number of IMAGINE licenses we have I can compute statistics and pyramids on 16 rasters at a time.  It's easy to set up a batch process using the IMAGINE batch processing wizard.  This is a real time saver for large tiled datasets.

ArcGIS 10 Large Floating Point Raster Display Bug

For those of you, like me, that work with very large raster datasets, ArcGIS 10 has a nasty bug that causes floating point rasters to not display at certain scales.  ESRI Support lists this bug as # NIM061128.  The problem does not exist in ArcGIS 9.x releases so this is obviously due to some of the underlying modifications made to ArcGIS raster handling at version 10.  It's a bit difficult to work with your data if you cannot see it, so we will be holding off on making the full transition to version 10 until this bug is fixed.  Right now I have version 10 running on a virtual machine I set up using VMware Workstation.  This allows me to run ArcGIS 10 and ArcGIS 9.3 on the same computer.