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SRTM: was it worth it?

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#1
merft

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"I'm curious about opinions/experiences related to the quality of SRTM data after the release of the ""final"" version of the US.

I
have to admit that I was really excited about this project years ago
when it was first mentioned and have been periodically watching the
data as it has been produced. However, with the release of the ""final""
SRTM dataset for the US, I have to admit I'm extremely disappointed
with the quality of the SRTM product.

I have downloaded a
variety of pre-release 90m versions (with holes in snow/water covered
areas) and was okay with those because they were pre-release. I was
able to fill holes with GTOPO/GLOBE (for areas outside the US) and with
250k DEMs (inside the US).

Yesterday, for the first time, I
downloaded the ""final"" 90m data for the US. Which supposedly (according
to the website) had corrected the null values with NGA DTED data. In
the areas I was working with (southern Colorado), the null values were
filled, but with a value of 0. What is the deal? The souther Rockies
now are filled with what looks like a bunch of extinct volcanoes.

Now
this was a small sampling, but if this is the quality of the data my
tax dollars are paying for, I am VERY concerned. I hear the european
group working on fixing the SRTM data are actually digitizing the
contours in the null areas from maps and gridding those values in.
Personally, if the USGS/NASA cannot put the correct values in they
should leave the values as NULL and not obviously incorrect data.

-Tom "

#2
Hans van der Maarel

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Being
European, I'm obviously very happy with the fact the data is available,
for free. I do agree with you w.r.t. null values. If an elevation is
set to 'null', it's clear there's no data there. If it's set to 0, you
would normally assume that's the correct elevation at that location.

Any chance of going back to the pre-release version with the gaps? 3DNature's SRTMFill does a pretty good job of fixing those.

Hans van der Maarel - Cartotalk Editor
Red Geographics
Email: hans@redgeographics.com / Twitter: @redgeographics

#3
Martin Gamache

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Is it worth it?

I
guess it depends what you want to do with it and where you are from,
the overwhelming word out there is that this was a very successful
mission. The current issue of PE&RS (March 2006) is devoted to SRTM
data and provides a good perspective on the mission, data quality and
applications, it is well worth digging up and reading. Considering the
scope and the end product I think it was well worth it despite all the
data problems and promises to be a very useful dataset for a wide range
of users, not just cartographers.

My biggest issue is that NGA refuses to release the higher resolution data outside the US.

Hopefully it will lead to more missions that address the voids and improve on the initial dataset.

mg










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