HiRISE DEM's Options

[djellison]

Late last week I stumbled upon a few HiRISE derived DEM's (Randy Kirk works his magic once again!)

http://webgis.wr.usgs.gov/ftphirise/index.jsp (URL now down)

I'm working on both Vic Crater and the Columbia Hills. Fortunately, now I've got a Mac, I can use ISIS. I've figured out a fairly simple flow ( isis2raw as 16 bit unsigned, and then imported into Photoshop ) to take DEM CUB's and make 16 bit PNG's

Just to demo how important that is for me as an animator - sliced comparisons of 8bit vs 16 bit.

A busy week unfortunately, but animations of various sorts are in the pipeline.

Attached thumbnail(s)

 

[RRussman]

Doug, I’m pretty sure everything is matched to MOLA after 2000, but as you point out, the sampling is sparse even along track. By sparse I mean there are 48,211 mola points (PEDR) over several tracks/orbits in the map extent, and yes, some dtms are far more populated than others are. The HRSC and HiRise products are continuous data sets with much finer resolution. An excerpt from the literature on the resolution mismatch:

“Because of the low horizontal resolution of the MOLA data set compared to HiRISE images, vertical accuracy will likely be governed by the difference between localized topographic features and the broader-scale relief as measured by the altimetry, and may be several meters. The resolution mismatch between the two data sets is likely to make direct use of MOLA for horizontal control almost impossible. Our approach is to control lower-resolution images to a shaded relief product generated from MOLA data gridded at 1/256 or 231 m/pixel, then to transfer control from these images to the high-resolution stereopair.” (McKewen, etal, 2007) (from Wiley/JGR, access required for full text)

The discontinuity is most noticeable in the northern portion of the map with the DTEEC_010573_1755_010639_1755_U01 appearing offset more, relative to the adjacent overlapping regions, as well as the general flow of the collective model at multi-product extents. It might simply be that this model received less rigorous processing to the north and away from the msl region of interest.
“Since editing is extremely time-consuming, it is usually done on easily corrected errors and in the areas of most interest to the researcher.” (From the About DTMs page)

Paolo, I appreciate your suggestions and will experiment with re-projecting the dtms. I have experimented with re-geo-referencing the orthos (3rd order polynomial RMS:~0.7). The distortions were minimal, but as you mentioned, they lose their distinct relationship to the dtm and coordinate system, not to mention time consuming, tedious work. It makes your solution sound very appealing.

Phil, I am suspicious of every data set I open, especially my own