I spoke with some folks from the Texas Natural Resources Information System (TNRIS) this week. Basically, they are a clearinghouse of GIS data covering the state of Texas. They provide DEMs and aerial imagery and DOQs and that sort of data free of charge. They elected to store their newest set of imagery in JPEG 2000 format so as to take advantage of the 4-band storage format. This lets them maintain a single set of files but provide both full-color and color-infrared imagery. A lot of the consumers of this data are ESRI users, and it's a simple matter in the symbology dialog of ArcMap to assign Red, Green, and Blue color to three of the four bands in the file so you can view the raster either as full-color or as color-infrared.
The folks I was speaking to said they'd gotten some calls from MicroStation users saying they couldn't do the same thing and asking if the TNRIS staff had any suggestions. They, in turn, asked me. I said I didn't know but I'd ask around... thus this post.
I know from digging in the on-line help that MicroStation supports JPEG 2000 in RGB and RGB Alpha modes. When I tried viewing one of the rasters in MicroStation or BentleyMap, however, it came in as RGB only and I didn't (with my neophyte MicroStation skills) find a way to adjust the symbology the way I wanted.
So I have three specific questions: is RGB Alpha the same thing as RGB+Infrared? If a raster has 4 bands, can you adjust which ones are displayed and what color is assigned to each in MicroStation? What about Descartes?
Hi Kim,
Below are some answers to your questions :
"Is RGB Alpha the same thing as RGB+Infrared?"
No. The alpha information specify the opacity of the pixels. This is this information that is used to give a transparency effect to the image.
RGB+infrared images are multispectral images. Multispectral images differ from convertional images as they contained measurement from non-visible light (in that case infrared light or radiation).
"If a raster has 4 bands, can you adjust which ones are displayed and what color is assigned to each in MicroStation?"
In Athens, you will be able to do that with the raster configuration variable MS_RASTER_IMG_CHANNELS but only for Erdas IMG images, not with JPEG 2000 or any other file formats.
"What about Descartes?"
Descartes doesn't support multispectral imagery.
Note that Microstation doesn't supports JPEG 2000 image in RGB Alpha mode. This was a mistake that has been corrected in the Microstation Athens documentation.
Thanks,
Mathieu