time-aware composite mosaic dataset and MaxPS

Question

Hello,

I am creating a composite mosaic dataset from three other mosaic datasets, each of which holds four orthophoto tiles from different years: 2004, 2009, and 2013. The goal was to create a time-aware layer and use the time slider to demonstrate this functionality for my students. The extent of the tiles are the same across years and the coordinate system is all state plane (feet), the only difference between the datasets is that the 2009 photos are higher resolution (0.5 ft) than the 2004 and 2013 (1 ft). After I combine the mosaic datasets into the master mosaic dataset and enable time on the layer, ArcMap does not display the 2009 set when the time slider comes to that year. It's footprint appears, but nothing else, and the other two years display just fine.

At first, I tried using "build overviews" to see if that would fix it. It didn't. Then, I looked at the master mosaic dataset's footprint layer. I noticed that identical values are produced for MinPS, MaxPS, LowPS, and HighPS for the 2004 and 2013 sets in the master dataset's footprint attribute table. The LowPS for the 2009 orthos is (expectedly) 0.5, reflecting the higher resolution of this series. However, the MaxPS value is set to 1 for the 2009 set, while for the 2004 and 2013 sets the MaxPS value is 270.(Please see attached screenshot of the attribute table showing.)

[ATTACH=CONFIG]34089[/ATTACH]

I still wasn't quite sure what the MaxPS field does even after reading the help article on cell size ranges, but I changed it to 270 for the 2009 set, as it was set for the 2004 and 2013 sets, and then it displayed. In order to understand this better, I kept changing the value until I discovered that the image would appear if I set the value to 6 or greater. When set to 5 or less, the image would not appear when moving the time slider to 2009. I would LOVE it if someone can explain to me why so that I can explain it to my students!

Thanks!
 -Neil

composite_mosaic_dataset_footprint_table.png

larryzhang1 · Answer

...

Now my question is, why don't I have overviews generated for the master mosaic dataset? Even after building overviews, there are no additional footprints and attribute records in the footprint layer. Overviews were created for the three component mosaic datasets, so why not for the master mosaic dataset, which is a mosaic of all three? And why would creating the master mosaic compute such a small MaxPS for the 2009 mosaic in the first place?

Neil,

On the creation of overviews on �??master�?? MD, it can be treated as limitations or bugs, which are related to �??composite�?? MD & �??derived�?? MD from other MDs.  Pls also refer to the discussion at http://forums.arcgis.com/threads/109836-Best-Practices-Raster-Catalog-gt-Image-Service?p=390263&viewfull=1#post390263

Personally, on �??master�?? MD (with time-aware capability), it is not good idea to create overviews here, because it might �??likely�?? blend the time-serial rasters, if not done properly in operation.  In fact, it is also not one of major interests for time-aware function�?�

NeilCurri · Answer

Thanks, Larry. I think I get it.

First, because I'm working in SP NAD83 Feet, I need to convert the MaxPS to meters, then apply the equation. So, for MaxPS 270, that converts to about 80 meters. Plug that into the equation, and I should see the image at scales higher than about 300,000. When the MaxPS is 1, that's about 0.3 meters, so I don't see the image until I zoom in to about 1:1,100 meters. The extent of all four tiles in my study area is just over 1:7,000. So, when I increase the MaxPS up to 6, that's 1.8 meters and computes to a scale of 1: 6,800, and so the image appears.

Now my question is, why don't I have overviews generated for the master mosaic dataset? Even after building overviews, there are no additional footprints and attribute records in the footprint layer. Overviews were created for the three component mosaic datasets, so why not for the master mosaic dataset, which is a mosaic of all three? And why would creating the master mosaic compute such a small MaxPS for the 2009 mosaic in the first place?

larryzhang1 · Answer

Neil,

Firstly, it is feasible to make 2009 (0.15-m resolution) visible via �??building overviews in MD 2009�?? without changing MaxPS. For larger time-serial master MD, in fact, the creation of overviews is necessary and common in practice. Pls refer to the discussion at http://forums.arcgis.com/threads/109836-Best-Practices-Raster-Catalog-gt-Image-Service?p=390263&viewfull=1#post390263

Secondly, MinPS and MaxPS values are derived from LowPS and HighPS that control which raster will be used to create the dynamically mosaicked image at particular scales (or resolutions of the display, or image request, or the performance)�?�

So, let�??s TRY your question together (hopefully, understand correctly and also explain clearly):

[INDENT]From 80 converted from 270 in MaxPS in 2004 & 2013 (0.3-m resolution), the map scale to display is roughly obtained:  80*96/0.0254=310,000, which means that you can see your photos at the scales at larger than 1: 300,000 (saying, 1:150,000), without overviews. Inversely, when increasing the value of MaxPS, those images would be invisible, without overviews.

In fact, on your practice, if using 1.83 from 6 or larger in 2009 (0.15-m resolution), the rasters can display properly, which means that the map scale is: 1:7,000. Otherwise, it requests higher mapping scales to display 0.15-m photos; or, the overviews in MD should be created, if the value of MaxPS increased, saying, 1.32 (4.35 feet) in MaxPS  �?�[/INDENT]