Raster data advise

[Willemvan_der_Meulen]

I supplied raster image data to an ArcGis user which complains about immage data size, it slows its computer down........

Immage data are georeferenced ecw tiles obtained using aerial photography. The whole set consist of about 20 thousand tiles high quality images (pixels are 7 by 7cm pixels), each tile being 200 x 200 meters.

The client asked me to make the tiles bigger, but I would think increasing the tile size does not help much if at all. One could increase a tile to for example 1 x 1km (same pixel size); this would make the tiles bigger and would not help much if at all. Please advise me on this. Currently each tile is about 300kb each (unpacked 11MB).

I suggested the following: In the GIS program I use myself I actualy adjust the setting to only display the images when zoomed beyond a certain scale, for example 1:1000. This way ony few images need to be loaded and does not slow down the program any more. I am quite shore this will be possible with ArcGis as wel. I would think this would be the best solution.

If one still wants to see the immage as a whole when zoomed out one should generate low quality images which are smaler in size and switch on and of depending on the zoom scale

BTW telling the client he should get a bigger computer and jack up his skills might be the correct answer but is not going to help me, like in most fields client is king.


Thanks,

Willem

[NiklasNorrthon]

Just a few suggestions:

• Don't add the images themselfs to ArcMap, access them via Mosaic Datasets or unmanaged catalogs instead
• Build pyramids (or overviews in case of Mosaic Datasets)
• Don't store all images in the same directory, spread them among several subdirectories instead

[MelanieHarlow]

Yes, you can set the imagery to display at a specific scale. This has been a function in ArcGIS (ArcMap, etc) for some time. I would group all the layers into a group layer and set the visible scale on that group layer. Here's a link to a 9.2 help topic (if they're using an older version of ArcGIS): http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=Displaying_layers_at_certain_scales
The functionality has been improved, but works basically the same in the later versions of ArcGIS.

Like Niklas suggested I would create a mosaic dataset. However, this only works in version 10.0 and higher. So if the user is not using the latest version they will not be able to access the mosaic dataset. So his second option of an unmanaged raster catalog is excellent. There's also a setting on a raster catalog to modify what you see. By default the user will see a wireframe outlining each image in the catalog. When they zoom in to an area with 9 or fewer images, they will see the imagery. This is similar to your suggestion of a visible scale setting. You can change this default setting on the raster catalog Layer Properties dialog box under the Display tab.