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miksmith
Osiris (Active Member)
Joined: 15 Oct 2005
Posts: 6
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 Posted: Sat Oct 15, 2005 2:26 pm Post subject: ArcIMS Server Data at USGS |
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Hi
I've recently been loading ArcIMS data from
http://webgis.wr.usgs.gov
on top of some MOLA data downloaded from PDS Geosciences. I have run the pds2world.pl Perl script to generate the headers and then loaded the raw data in to ArcGIS, using the Mars_2000Sphere.prj projection file. That all works fine *except* that the ArcIMS data only loads up over the western half of the MOLA data.
Loading this up the other way around (ArcIMS first, MOLA second) things work fine. Is this something to do with geographic/projected coordinates and on-the-fly conversion by ArcGIS??
Thanks for any pointers!
mike
P.S. Slightly related query: is there any way to save the "original" data from ArcIMS/WMS? |
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thare
GIS Support Team
Joined: 22 Mar 2004
Posts: 657
Location: USGS Astrogeology Research Program, Flagstaff, AZ
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| Posted: Tue Oct 18, 2005 8:26 am Post subject: |
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Your problem probably has to do with the difference in defined center longitudes (clon). For the planetary on-line mapping services we have defaulted to present Mars with a clon=0 (longitude system using -180 to 180). This is generally how martian global maps are published. In our experience, by using a clon=0, it will be supported by more GIS/RS applications and WMS client applications. Unfortunately, many of the latest datasets have been released with a clon=180 (longitude system using 0 to 360). Now are servers also serve their data in decimal degrees (e.g. Mars 2000.prj), but they can be projected on-the-fly to most projections.
So the MOLA files you have converted, using pds2world.pl, have been released using the clon=180 system (and most likely in meters using Equidistant Cylindrical projection, aka Simple Cylindrical - we do have pds2world_dd.pl to create decimal degree registered worldfiles). Since this is a just a shift in longitude it can be fairly easy by just fixing the worldfile. However, doing this for a bunch of files can be a pain. Here are a couple subjects on the topic:
http://isis.astrogeology.usgs.gov/IsisSupport/viewtopic.php?t=352
http://isis.astrogeology.usgs.gov/IsisSupport/viewtopic.php?t=360
Side note: Another issue using the PDS MOLA headers is that the radius is truncated at the kilometer scale. The IAU has defined the radius of Mars should be set as 3396.19 km/p not 3396.0 km/p. This will slightly change the calculated meters/pixel cellsize.
http://isis.astrogeology.usgs.gov/IsisSupport/viewtopic.php?t=341
http://isis.astrogeology.usgs.gov/IsisSupport/viewtopic.php?t=389
For datasets with a clon=180, you can correctly use ArcMap: see example projection file “Mars2000_EquidistantCylindrical_clon180.prj" at http://isis.astrogeology.usgs.gov/IsisSupport/viewtopic.php?t=389
But ArcMap, as you have seen, you will have issues displaying the ArcIMS services correctly because it has to swap the image sides on-the-fly. In theory it should work but in practice it doesn’t work. I have heard ESRI is working on this issue for the next version, but it is a pretty tricky issue.
Side note: Using clon=180 for datasets will also cause ArcGlobe to potential show only one side of the globe. So using datasets defined using clon=0 will work better for this application too.
What to do:
I would suggest NOT using the PDS MOLA files (with worldfiles generated by pds2world.pl) if you want to work with planetary ArcIMS or WMS servers or ISIS generated files. Why – because the PDS labels use a truncated radius and for the servers because it is defined using a clon=180.
http://isis.astrogeology.usgs.gov/IsisSupport/viewtopic.php?t=439
This is why I have re-released the MOLA datasets generated with labels regenerated in ISIS using 3396190.0 for the radius for both clon=0 and clon=180.
http://isis.astrogeology.usgs.gov/IsisSupport/viewtopic.php?t=439
Conclusion: This whole topics is painful when trying to use datasets from multiple locations and using existing GIS/RS tools. We are slowly trying to work with groups so that datasets are more consistently released and possibly released with GIS compatible labels.
Trent
Last edited by thare on Tue Oct 18, 2005 9:09 am; edited 4 times in total |
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thare
GIS Support Team
Joined: 22 Mar 2004
Posts: 657
Location: USGS Astrogeology Research Program, Flagstaff, AZ
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| Posted: Tue Oct 18, 2005 8:49 am Post subject: |
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For the question, " saving the original data" - The answer would be yes and no.
Vector Layers
Any of the vector layers (nomenclature, geology, craters, etc.) can be "clipped-n-shipped" from the intermediate viewer. How: In any the intermediate viewers, zoom into your area of interest, turn on the layers you wish to clip-n-ship and download, and use the "extract" button. This will clip out the information for each vector layer turned on, convert them to shapefiles, and bundle them up into a zip file. All vector layers should be available for download from our ftp download site also. Downloading them from the ftp site should also have the metadata (or at least a readme). I have not figured out how to get the metadata to get bundled using the clip-n-ship function.
For the Mars intermediate viewers visit: http://webgis.wr.usgs.gov/mars.htm
Raster Layers
I believe GIS streamed layers are the way of the future but given currently internet speeds, I admit, it can be a little slow. Try the ArcIMS servers in ArcGlobe 9.1 – way cool but again a little slow. To help with this, we have recently worked with ESRI to help them build a “WMS connect tool” (this is based and similar to their Terraserver GP download tool).This allows the user to point to any compliant WMS server, specify the layer, the style, cellsize, extent and it will automate downloading the image tiles from the server and retile them into a single local file. This even works for 16bit MOLA data (although you have to convert the data from unsigned 16bit to signed 16bit. But if you wrap this into a model, it does that for you too. We are also just about to test streaming a Geotiff, which may support 32 bit files. The tool is still beta and only works for ArcMap version 9.1 and we have received permission to release it. I need a few more days to bundle the tool with some pre-built models to help users grab MDIM21, MOLA, colored MOLA, Slope, hillshades, and other variants. I will release it back here for users to Beta test. Eventually it may be built into ArcMap.
It will be easy for users to hammer the servers so we are hoping users will not, for example, ask for global datasets at full resolution. For global datasets, we hope the user will default to larger cellsize and then once zoomed into an area of interest request full-resolution.
Note that nearly all the layers (raster and vector) that are in the servers should be available for download too. ftp://ftpflag.wr.usgs.gov/dist/pigpen/
Note 2: My ArcIMS servers will support WMS protocals but currently it is broken. I need our gurus to fix a couple other items before I can tackle this issue. I am hoping to fix this within the month.
Trent |
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