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Subhabose

Georeferencing PDS images in ENVI

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I want to georeference an M3 image (obtained via PDS) in ENVI. I was following "Assigning Map Information to PDS Images in ENVI", posted by Dr June Wang. I was able to perform most of the steps. Yet when the process is complete, it seems that the georeferencing is not correct. I have attached a couple of screenshots from the M3 image I was working with.

To check the accuracy of georeferencing, I cross-checked the location from Google Moon and found that there are a lot of discrepancies between the 'georeferenced' M3 image and Google Moon. In the 'Edit Map Information' window, I entered X-pixel and Y-pixel sizes as 140. Please let me know if this is correct. When I cross-checked with Google Moon, the top of the image should have latitude as north and the bottom the image as south (also verified from LOC file of the M3 image). Please help.

CursorLocation.jpg

EditMapInfo.jpg

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Hi Subhabose,
Would you please give me more information about the M3 image you are working with? e.g., product ID and the projection name. I will take further look. Thanks,
June

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Hi,

The product ID is M3G20081229T022350. The projection used was Lunar Sinusoidal. I tried to follow the steps prescribed by you for assigning map information to PDS images in ENVI.

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Hi Subhabose,
The product ID you gave was not a complete product ID. This value can be found in the product label file. From your ID I cannot tell what type of product you used. Is it the L0 raw data, or the L1B calibrated image, which has 3 versions, either Version1, V2 or V3? Or the L2 reflectance image?
Please take a look of below help page. At the bottom of the right panel, you will see some additional M3 resource, including M3 ENVI User's Guide,working with M3 Data, Working with M3 L1B Data, M3 Data Tutorial and a few others. 
http://ode.rsl.wustl.edu/moon/pagehelp/quickstartguide/index.html?isros_chandrayaans_m3.htm
Assuming you use the Version3 L1B calibrated image, e.g., ' M3G20081229T022350_V03_RDN', you can access  the  location  and  geometry  information  in  the *.LOC and *.OBS files and relate it to the spectra of the *.RDN files using ENVI as documented in the file 'M3 ENVI User's Guide'. And you can use GLT in ENVI to do the georeference.

As for your question about map projection, from your screen copies, I can only tell the Datum you used are not correct. Because WGS-84 is used for Earth. If you can send me the strings that you have updated in three files datum.txt, ellipse.txt, map_proj.txt, I can dig more into your issues. Thanks,
June

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Hi Subhabose,
The ‘ellipse.txt’ file looks fine to me. In datum.txt, you had an extra ‘,’ in the last line. The correct string would be below.
‘D_Moon_2000, GCS_Moon_2000, 0,0,0’
In file ‘map_proj.txt’, I saw your definition for the Moon North Polar Stereographic projection. Since the maximum and minimum latitude for your data are 59.676 and -1.151 degrees, I would not suggest using the North Polar Stereographic projection.

 

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Hi June,

I want to georeference an M3 image (M3G20090205T094623_V01_RFL), I have added Lunar south polar stereographic projection with D_Moon_2000 as datum. As you mentioned I have added the ellipse.txt (GCS_Moon_2000, 1737400.0, 1737400.0), datum.txt (D_Moon_2000, GCS_Moon_2000, 0,0,0) and map_proj.txt (31, 1737400.0, 1737400.0, -90.000000, 0.000000, 0., 0., Moon South Polar Stereographic). But after applying GLT procedure, I am getting georefernced image with no data mostly. Please help me to resolve this issue.

Thanks,

Raj.

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Hi Raj,

Have you tried the docs at http://ode.rsl.wustl.edu/moon/pagehelp/quickstartguide/index.html?isros_chandrayaans_m3.htm?  At the bottom of the page, you will see some additional M3 resource, including M3 ENVI User's Guide,working with M3 Data, Working with M3 L1B Data, M3 Data Tutorial and a few others.  I also attached below another instruction with other example data other than yours. Please try with your own data and let me know if it works for you. Thanks,
June

Instruction to work with M3 level2 data.pdf

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Hello.

I actually wanted to ask the about the ellipse data representation 

 

GCS_Moon_2000, 1737400.0,1737400.0

 

What does GCS_Moon_2000 represents?

The other two repsents the minor and major axes radius of moon

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When I georeferenced the M3 data in either Sinusoidal or Mollweide projection, why isn't the ENVI asking for latitude?  Its just asking about longitide and false easting and northing.

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12 hours ago, June Wang said:

Hi Akash,

no need of central_latitude for both projections.
GCS_MOON_2000 is a geographic coordinate system, whose datum is the D_Moon_2000 in GIS software. The other two are major axis and minor axis in meters.
Please read 'LRO Project and LGCWG White Paper' at https://lunar.gsfc.nasa.gov/library/LunCoordWhitePaper-10-08.pdf for more hep

Thank you so much June for all the help. 

Whatever you suggested is workimg and of great help. 

I just have a last query that how to decide which projection is best for your study. For eg if I want to study the mineral composition around south western part of Moon, whether I should go for Sinusoidal curve or Molleweide or equatorial map projection? 

Thank you so much once again  for your time.

 

 

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That is a very good question but hard to answer. When choosing a projection, you need to consider about how you would like to use the map and what your research interest is. No map is error free. Do you like to preserve the shape, or preserve the area, or preserve the scale, or the direction, or something else?

If you want to study the mineral composition on the moon. E.g., you want to know the certain coverage of a mineral, if areas are not in true proportion, the map will give false interpolation of the data. So choosing equal-area projections will better fit this need. The size of any area on an equal-area projection map is in true proportion to its size on the moon. The decision also depends on the location of the area to be mapped. Is it a polar, mid-latitude, or equatorial region? A reasonable projection can minimize the distortion for your area of interest.

Sinusoidal and Molleweide projections are both a pseudocylindrical equal-area projection. Sinusoidal projection represents the poles as points. There is no distortion at the equator and the prime meridian, but the distortion gets worse the further away from either. Scale is constant along the central meridian and all parallels.

Molleweide projection represents the equator as a straight horizontal line perpendicular to a central meridian one-half its length. The 90th meridians are circular arcs and all other meridians are equally spaced elliptical arcs. The parallels are unequally spaced straight lines parallel to each other. Poles are points. Scale is true along latitudes 40°44' N and S. Distortion increases with distance from these lines and becomes severe at the edges of the projection. Equal-area is preserved for this projection but at the expense of shape distortion. Shape is not distorted at the intersection of the central meridian and latitudes 40°44' N and S. Distortion increases outward from these points and becomes severe at the edges of the projection.

You may notice Simple Cylindrical, or Equirectangular, or Equidistant Cylindrical projection are used in many planetary maps. This projection is very simple to construct and it converts a globe into a Cartesian grid. When the equator is used as the standard parallel, the grid cells are perfect squares, but if any other parallel is used, the grids are rectangular. The scale is correct along the meridians and the standard parallels for this projection. Distortion increases as the distance from the standard parallels increases. The poles are represented as straight lines across the top and bottom of the map.

When read below book, you can get more pros and cons for different maps projections and make your own decision. Thanks,

June

Snyder, John P., 1987, Map Projections, A Working Manual, U.S. Geological Survey Professional Paper 1395, 385p. http://pubs.er.usgs.gov/publication/pp1395

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Hello June

I was studying about the magnetic field and solar wind properties of lunar surface.  

Can you suggest which data should I go for.

Thank you for your time 

Regards

Akash

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Hi Akash,

PDS Geosciences node archives the Lunar Prospector MAG/ER raw data, basically the downlinked telemetry format, available at https://pds-geosciences.wustl.edu/missions/lunarp/index.htm. You can find more calibrated and derived MAG data from the PDS PPI node, https://pds-ppi.igpp.ucla.edu/mission/Lunar%20Prospector/LP/MAG#. This link describes the magnetometer experiment at PPI and provides links to the data sets that they have.

Most of the raw, calibrated and derived MAG data can be searched and downloaded from the Lunar ODE web, https://ode.rsl.wustl.edu/moon/indexProductSearch.aspx. Please see below attached example data product search page, and let us know if you have any problem to access the data. Thanks,

June

Capture_LP.PNG

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Actually I wanted to know how to add map_proj_txt and datum_txt in ENVI software of M3 RFL image to do edit of map projection. Can you please explain it in detail?

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Hello Mam,

I am using M3 RFL image for mineral mapping in ENVI software. To do that I have to do geo-referencing on RFL image. My file id is m3g20090713t192732_v01_rfl. I have downloaded LOC file of my study area from ODE website.

For geo-referencing I have to edit datum_text, ellipse_text and map_proj_text file in ENVI software installation. I don't understand what is the exact string to add for this image?For further processing I have to done map projection and here I am still stuck in it. Please help me to solve this. I hereby attach those three text files which I have edited in the last for your reference and also attach one screenshot image where in output projection those moon related options are not there. Please help me to solve this.

Screenshot (162).png

datum.txt ellipse.txt map_proj.txt

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All your three files look good to me. I downloaded the data and tried the Georeference from IGM, and projected the data using your projection string. It took more than 1 hour for all the process to be finished. The results look good when compared with a LROC basemap. If you can send me more details where you stuck in I can help you from there. Thanks,

June

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Hello June,

Actually I am confused to select the exact option in Input geometry projection and output projection of geo-referencing. In customized map projection tool I have select Transverse Mercator as projection type and sample Transverse Mercator as projection name. Is it okay?

I hereby attach some screenshots those steps regarding map projection for your reference. Please let me know is it okay? or I should change the projection regarding my RFL image? After geo-referencing how to compare my projected image with the LROC base map? Is this base map available in ODE site to download? 

Screenshot (163).png

Screenshot (164).png

Screenshot (165).png

Screenshot (166).png

Screenshot (167).png

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Fig. 1 is correct. In fig.1, you used the Sample Transverse Mercator. I noticed it is a default projection template string in map_proj.txt in ENVI. Since you already edited the radius in the template string. It is OK to use it. But you could also copy this template and make changes to the parameters and projection name as you need it.

In Fig. 2, you can output GeorefFilename to the directory you like and keep other default settings, then click ok.

image.png.2afa79baed7c8679542e03039bc0928f.png

You can refer to the file "Instruction to work with M3 level2 data.pdf" posted on November 14, 2019 in the above.

BTW, WAC mosaics can be downloaded from http://wms.lroc.asu.edu/lroc/view_rdr/WAC_GLOBAL

Please let me know if you need more help. Thanks,

June 

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