Questions:
- How do I set up GeoMedia to do coordinate transformations between GDA94 and AGD66 / AGD84?
- How do I optimise my image display in GeoMedia?
- What are the Oracle requirements for the Oracle Object Model dataserver when using GeoMedia application version 6.1?
- What Oracle privileges are required for various classes of users in GeoMedia, i.e. Master, Editor, or Viewer?
- What is the best performing raster format?
Q: How do I set up GeoMedia to do coordinate transformations between GDA94 and AGD66 / AGD84?
A: GeoMedia uses the Canadian National Transformation (2.0) model to do coordinate transformations. This is more accurate than the 7 point transformation. Before any transformations are done in a GeoWorkspace, ensure that the Canadian files are in place.
For the Canadian National Transformation (2.0) model a distortion or grid file is needed. The Canadian National Transformation includes both a datum change by a similarity transformation and a distortion model to compensate for the underlying distortions in the AGD network.
These distortion files are not supplied by Intergraph but can be acquired from the following web page: www.icsm.gov.au/icsm/gda/gdatm
For more info on GDA, please visit www.icsm.gov.au/icsm/gda/index.html
Step 1: Unzip the ‘A66 National (13.09.01).gsb file to GeoMedia or GeoMedia Pro installed directory in the… Program\cssruntm\cfg\canada folder.
Step 2: Rename the file to A66National.gsb.
Step 3: Open the area.ini file in the same directory with notepad or any text file editor.
Step 4: Change the current text to be the same as the *.gsb file. In this case replace the NTv2 with A66National.
GeoMedia is now set up to do datum transformations between GDA94 and AGD66.
Q: How do I optimise my image display in GeoMedia?
A: GeoMedia Hot Fixes often include incremental performance enhancements for raster data. Be sure you have the latest HotFix.
Performance is a function of several variables. Network performance, image format, image compression, and pre-processing are all factors, as is the hardware doing the display.
Hardware - We suggest high performance CPUs (2GHz, ample memory (1GB) and hard disk space (sufficient for local image storage) and fast network cards.
Compression - Compressed images are small, but require time to decompress. Performance is optimised when you have sufficient disk space to store uncompressed images locally. If your images are compressed, there will be a performance hit. If the images are stored on a network drive, there will be a performance hit.
Format - Some formats are not suitable for image storage. Specifically, JFIF (.jpg) images should be avoided. Bitmap files (.bmp) should be avoided.
Display Resolution - Your display device has limited capabilities. Your desktop settings determine the number of pixels shown on your monitor. Generally, resolutions will be 1024 X 768 or 1280 X 1024. These resolutions indicate that your monitor is capable of displaying 3/4 to 1.5 million pixels. If your image has high resolution, and the images cover the screen, the software will have to 'subsample' your image to fill the display i.e., read the whole file, and throw away those pixels which don't get displayed. When the number of pixels in the image is very large (number of rows times number of columns), large percentages of the image will be read, but not displayed. The monitor can only show you so many pixels, regardless of the number in the image.
Overviews - GeoMedia supports the use of Overviews. Overviews are copies of your image at reduced resolutions. GeoMedia will use these Overviews to display your image extremely rapidly, if they exist. Since your screen can display only a million or so pixels, we simply read the overview that contains that number of pixels. As you zoom in or out, GeoMedia automatically swaps overviews, to maximize image display performance, while maintaining the highest image quality. Virtual overviews already exist for MrSID, ECW and some other formats, and are used by GeoMedia automatically. Other raster formats do not contain overviews, but they can be added. We suggest you install the ImageStation Raster Utilities (ISRU) from http://support.intergraph.com/Downloads/Tools.asp. One of the tools contained in ISRU can add overviews to your existing TIFF files (and INGR raster file formats as well). The overviews are stored in the file itself, which incurs a minor cost by increasing the file size by no more than 1/3 of the original size.
Optimal display performance is achieved for a given hardware configuration by having uncompressed TIFF files with overviews local to the machine displaying them. Networked files, compressed files, other file formats, and the lack of overviews will all slow the image display.
Q: What are the Oracle requirements for the Oracle Object Model dataserver when using GeoMedia application version 6.1?
A: Beginning with the release of GeoMedia 6.1, Oracle 10g Enterprise Edition Release 10.1 or later is required. Both the standard engine and the enterprise edition are fully supported.
Oracle 10.2.0.3 or later is recommended.
Oracle Express 10G is also supported.
Oracle 11g is also supported.
For best results, use the latest client for connectivity. If you are accessing both 9i and 10g servers, use the 10g client.
Multiple Oracle Homes on the same client system can cause problems. For best results, use only one Oracle Home
Q: What Oracle privileges are required for various classes of users in GeoMedia, i.e. Master, Editor, or Viewer?
A: As DBA, you need to assign privileges on both the master schema and the GDOSYS metadata schema. By default, full access to GDOSYS is granted to PUBLIC. If you have kept that configuration, then all you need to do is grant privileges on the objects in your master data schema.
If you have changed the privileges on GDOSYS, you will have to assign specific privileges. Here is a breakdown of common user types (Note: In all cases SELECT is required on all GDOSYS objects):
MASTER USER: Owns all objects in the master schema. This user has the right to create database objects like tables, triggers, and sequences.
SELECT, INSERT, UPDATE, and DELETE privileges on all objects in GDOSYS.
SELECT, INSERT, UPDATE, and DELETE privileges on all objects in the master schema.
DATA EDITOR: Edit capability on some feature classes but not others. This user cannot create database objects.
SELECT, INSERT and UPDATE on GDOSYS's MODIFIEDTABLES and MODIFICATIONLOG tables.
SELECT, INSERT, UPDATE, and DELETE privileges on all schema tables and associated triggers and sequences where RW access is desired.
VIEWING USER: Read-Only access to all objects
SELECT on all GDOSYS tables
SELECT on all master schema tables
Q: What is the best performing raster format?
A: The following refers to continuous tone and color index images only. It is not applicable to binary raster.
If bandwidth is an issue, then either MrSID or ECW may be a good choice. I'm leaning more toward tiled TIFF with overviews, though. This encourages the use of multiple smaller images, instead of one large image. The combination of a single image feature class with spatial filters works great in GeoMedia v5.
ECW, MrSID, and JPEG2000 formats use wavelet compression. My understanding is that the decompression calculations are proportional to the resolution needed to fill the view at the desired scale. If you zoom in to the image, the calculations necessary to decompress smaller pixels is carried out, but only for the pixels in the view. When you zoom out, the calculations are not as extensive, but you have more area to decompress. This functionality is similar to the 'pre-generated' overviews we use with TIFF and INGR format data..
We have seen some improvements in display speed with MrSID in version 5. These are incremental - not a major change. Display of a 30000 row by 30000 column MrSID or ECW image will always be slower than the display of a similar TIFF with overviews, unless the network bandwidth (hence file size) becomes the limiting factor.
