Author Topic: Coordinate system problems with Mimas  (Read 2376 times)

m_valenti

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Coordinate system problems with Mimas
« on: April 28, 2015, 08:45:27 PM »
I've been working with DEMs from the moons of Saturn in ArcMap.  These DEMs were produce with Ames Stereo Pipeline and Isis 3 from Cassini ISS images.  The main thing I've been using ArcMap for, is to take profiles of the craters and to measure the average depths.  For this I need the the X axis of the profile graphs to be in meters, rather than degrees if I load the DEMs directly into ArcMap.  To solve this I had been using project raster to change the images to a projected coordinate system.

I just started working with Mimas, and I've been having a lot of trouble getting coordinate system to behave properly.  I've been using pretty much the same parameters as the other moons, with only the semi major and minor axis changed for Mimas.  When I drop the projected image into ArcMap, I get this error message: Warning, inconsistent extent.  Some of the images end up obviously warped in odd way.  If I take a profile of a crater that's listed as 139km across, it shows it to be around 1300km across.  There's definitely a problem happening with the units.  I tried a number of different things, but I haven't been able to get it to behave any better.  It doesn’t heIp that I current don't know much more than importing images and taking profiles in ArcMap.

Here are the parameters I've been using:

Projection: Plate_Carree
false_easting: 0.000000
false_northing: 0.000000
central_meridian: 0.000000
Linear Unit: Meter (1.000000)

Geographic Coordinate System: GCS_Mimas
Angular Unit: Degree (0.017453292519943295)
Prime Meridian: <custom> (0.000000000000000000)
Datum: D_custom
  Spheroid: custom
    Semimajor Axis: 207400.000000000000000000
    Semiminor Axis: 196800.000000000000000000
    Inverse Flattening: 19.566037735849051000

Any help with this would be appreciated.

thare

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Re: Coordinate system problems with Mimas
« Reply #1 on: April 29, 2015, 08:03:06 AM »
I was able to use the same custom radii as you mentioned in ArcMap 10.2.2. Generally Mimas is projected on a sphere when producing cartographic (map projected) products. In ISIS you have to override the input radii during cam2map if you go this route. But again a sphere or an ellipse didn't seem to matter.

To see if ArcMap is working okay with your base you can try to load our Mimas basemap layer. Now these WMS basemap think they are Earth but if you tell ArcMap's data frame to be Mimas they will project correctly. I was able to measure Herschel at 139km wide using the geodesic measure tool when using a degrees systems and plate carree (on Mimas).

To add a WMS layer, use the "add data from ArcGIS Online", search for Mimas and "add"
see: https://www.dropbox.com/s/7wdop6xfjmxtg32/ArcMap_custom_Mimas.jpg?dl=0

If the basemap doesn't match your images then double check the projection and make sure there is nothing odd for the center. If you are in a longitude domain of 360 and your center is 0, ArcMap will not work past 180. For a longitude domain of 360 you should set the center =180 which will help. But while ArcMap (and many other applications) may work in a longitude domain of 360 -- generally they much prefer lon. domain = 180 (and then a center of 0).

If ArcMap is still acting weird try a new project to see if something might have gone haywire.

let us know,
Trent

Herschel: http://planetarynames.wr.usgs.gov/Feature/2478;jsessionid=DA51FDFF3A8D1A3677A56D60A04FC1A8


m_valenti

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Re: Coordinate system problems with Mimas
« Reply #2 on: April 30, 2015, 02:53:08 PM »
I tried loading the Mimas basemap and I got this error: Invalid package, Error reading package contents. The version of ArcMap that I have is 10.0 (build 2414), in case that might be the problem.

The semi major and minor axis are added with the point2dem command in Stereo Pipeline.  I'm pretty sure the longitude domain stays the same as the Isis 3 default, which is 360 degrees, positive east.

thare

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Re: Coordinate system problems with Mimas
« Reply #3 on: May 01, 2015, 06:31:14 AM »
I will have to recommend upgrading to 10.2 or higher (just skip 10.1).  10.0 was released 5 years ago and like most software there have been many improvements. 10.3 has been out for almost 6 months and we have been using it successfully here.

Again using a 360 longitude domain is fine (probably even in ArcMap 10.0) as long as your center is not 0. If your center is defined as anything above 180 you should be fine. See if you can set the projection in the pipeline or run map2map in ISIS to change the projection, lonsys, or center longitude.

If you clear the projection in the data frame (data frame properties, coordinate system tab), and do not let ArcMap understand the current projection, you still should be able to run profiles in the meter defined Cartesian coordinate system. You just won'r be able to get geodesic measures like areas or lengths. But every time you add data or save something in ArcMap, it will again try to re-establish the projection so you might have to clear it again.

Other apps can help with profiling if you get stuck like Qview, Mirone, TuiView.

-Trent

older post with some simple video examples:
https://isis.astrogeology.usgs.gov/IsisSupport/index.php/topic,1253.msg8901.html#msg8901





« Last Edit: May 01, 2015, 06:34:30 AM by thare »

m_valenti

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Re: Coordinate system problems with Mimas
« Reply #4 on: May 04, 2015, 08:24:59 PM »
I did some trial and error with the projections in Isis 3, and I managed to find something that works.  I set longitude domain to 180 and left it as positive east in the maptemplate. For coordinate system, I used the D_Mimas_2000 datum and set the prime meridian to 180, and this seems to work.  The craters are coming out with close to the correct diameters.

However, I am having an Isis 3 projection issue.  One of the images is getting half  cut off once I set the longitude domain to 180.  I tried changing to centre longitude, and the shape of the projection changes, but the image is still cut off in the same place.  If you have an idea of how to fix this, it would help a lot.  I've always stuck to the standard 360E longitude, so this is mostly new to me.

(Also, the qview profile tool looks quite useful.  I'll have to look into it further.)

Here's the map template I used:
Code: [Select]
Group = Mapping
  ProjectionName     = Sinusoidal
  CenterLongitude    = 134.44778413852
  EquatorialRadius   = 207400.0 <meters>
  PolarRadius        = 190600.0 <meters>
  LatitudeType       = Planetocentric
  LongitudeDirection = PositiveEast
  LongitudeDomain    = 180
  PixelResolution    = 486.07945953393 <meters/pixel>
End_Group

Some example images projected with a 360E and 180E longitude domain:
ftp://ftp.seti.org/mvalenti/360E_lon.jpg
ftp://ftp.seti.org/mvalenti/180E_lon.jpg
« Last Edit: May 04, 2015, 08:27:37 PM by m_valenti »