Фотограмметрия для кухарок

Re: LRO: ISIS steps needed to use NAC images in ArcGIS (Open TH)
« Reply #1 on: June 07, 2010, 02:49:13 PM »

>>I want to use ArcGIS to measure crater diameters from LRO NAC images and have been told that >>I should use ISIS3 to perform photo-geometric corrections first.
>>I have a little experience with ISIS. Could someone advise me which ISIS3 programs I should >>use (and in which order)?
>>Terry.

That is correct. Before using and measuring features for any remotely sensed data, it is best to orthorectify the images. For GIS applications, it also best (really required) to map project the data (which usually happens during the orthorectification step). Processing planetary images from raw usually applies camera corrections, corrections based on the tracking information (SPICE), and eventually pushes the image pixels to the "correct" ground location through a radius model of the planet (when available). This is more important for images taken off-nadir and over large topographic changes in the image frame (e.g. cliffs, mountains, large crater rims).

That said, for high-resolution images like LROC NA and HiRISE images, while still important to orthorectify the image, it is probably okay to use for local feature measures. Orthorectifing a nadir-looking image probably won't change the feature sizes or feature locations (relative to each other) very much at all. I shouldn't be saying this but you can create a fake worldfile to define the pixel size. I would define the top left location in the worldfile as ~0,0 so the X,Y readout represents pixels (although the Y will be negative). This method should really only be used in a relative sense (local-only coordinates) as mapping to lon/lat will be difficult. Related: World files - what are they?

For ISIS3, you will need to wait for the release of 3.2.1 which is due out hopefully this month. This release largely contains the required LROC routines. During this release hopefully we will also release a short tutorial or simply list which steps are needed. These steps are generally (1) import, (2) SPICE initialization, (3) camera calibration, (4) optionally some type of filtering, (5) map projection (orthorect), (6) export. To export you can use the built-in ISIS3 routine isis2std (which creates a worldfile) or the stand-alone GDAL binaries. While HiRISE should be a good example on how this is done, hopefully LROC NA processing will not be as difficult. CTX might be a better example: Working with Mars Reconnaissance Orbiter CTX Data - Isis Workshop
HiRISE: Working with Mars Reconnaissance Orbiter HiRISE Data - Isis Workshop

Keep your eyes on the ISIS website which will announce the next release.

 

Pete and Al stand facing each other at Halo Crater and there's no one else in sight. Both are armed with Hasselblads and it's just a matter of who reaches his camera trigger first.