三个月前写的信，他老人家昨天才回，不过看后确实收获很多哟 :)

总结他老人家的意思：

1.摄影测量和计算机视觉在十年前是结合的黄金时段

2.目前计算机视觉主流已经走入recognition的时代

3.Geometry和recognition的结合目前鲜有人做，但不是没有可能

我的信：

Dear Professor Hartley:

I am a senior student major in photogrammetry at Wuhan University, China. Since I am very interested in computer vision, I am currently taking a research on photogrammetry and computer vision.

Recently I have read your paper "The relationship between photogrammetry and computer vision", SPIE, 1993. I have to admit that something you mentioned in the paper is quiet true. For example, on the PnP problem, "the photogrammetrist refused to even admit the possibility that there could be more than one solution." In fact, I have met this problem in one of my research projects, and I was surprised that, after decades the famous RANSAC paper has been published, in my textbook of photogrammetry, this multi-solution situation is still totally ignored.

After that, my interests on computer vision become deeper and deeper. I have been reading your famous book "Multiple View Geometry in Computer Vision". The compact form of projection matrix and the beauty of projective geometry amazed me. Though the essence of projection matrix in computer vision and collinear equation in photogrammetry are the same, the former reflects more beauty of mathematics.

However, after a little more dig, I found another paper, following your work ten years later, discussing about the relationship of the two fields--"Computer Vision and Photogrammetry--Mutual Questions: Geometry, Statistics and Cognition" by Wolfgang Forstner, a famous photogrammetrist. His paper made me more aware of the relationship, such as that we care more about precision, which is a feature and advantage derived from Geo-surveyings.

In conclusion, both the two papers expressed a hope that there should be more interaction between the two fields. Yet as far as I know, problem still exists. Apparently photogrammetry community has become more and more interested in computer vision approaches and International Society for Photogrammetry and Remote Sensing(ISPRS) have added a Commission III - Photogrammetric Computer Vision and Image Analysis(and the PCV 2010 is about be host in Paris, France). But it seems that little CV researchers pay much attention to this. And ICCV/ECCV have no such commission or workshop.

So, here is my question. It is about two decades after your paper on CV and PH, what's your comment now on the interaction of the two fields? Is there any "genuine exchange of ideas" as you mentition at the beginning of your paper? If the situation is stil the same, what do you think is the reason, and what can researchers do to improve this?

I am so sorry for being presumptuous to write to you and ask so many (maybe stupid and naive) questions. But I really can't help it, for I would like to devote my academic career to this interaction and exchange. As an undergraduate student who just steps into research areas, I really want some suggestions from masters like you.

I'm looking forward to your reply. And Thank you very much!

Yours sincerely,
Feng Chen

Richard Hartley教授（《Multiple View Geometry》作者）的回信：

Dear Feng Chen,

I apologize for the long delay in replying to your email. 
I am surprised that someone actually reads my paper from so long
ago. 

I think that the situation between photogrammetry and computer vision
is significantly improved these days, though the number of people who
do interact with both communities is quite small.  Of course Wolfgang
Foerstner is one of them, highly regarded in both communities.
There has of course been a lot of work more recently on all sorts
of minimal configurations, such as the work of David Nister, and this
is still ongoing.  In general, though, there does not seem to be a great
hope for future rapprochement of the Comptuer Vision and Photogrammetry
communities, partly because Computer Vision has moved on in a way
from a major interest in these topics.  Perhaps my book is partly
to blame for this, since it may have given a perception that the field
is very mature.  It is, of course, compared to where we were in the early
90s, but there are still people interested in Geometry in Computer Vision.
But it is not mainstream any more.  The major interest in Computer
Vision has returned to topics such as recognition.

In the early 90s, techniques for object recognition (probably the most
challenging and important goal in computer vision) have moved from
the geometric approach, as put forward by people like Joe Mundy
and others.  The work of him and others on image invariants, and
very geometric-based approaches to recognition led to the major
interest in geometry through the 1990s and early 2000s.  However,
ultimately, that theme of research was played out, and there was little
further headway to be made.  Current techniques have gone back
to less geometric techniques, such as the local feature descriptors, and such,
that have proved to be more successful ultimately, though some would still
find them unsatisfactory.  The idea of merging recognition using such
techniques with geometry is often talked about, but does not seem to
be followed much these days.

Anyway, thank you for your email, and I encourage you to keep thinking
of such topics

richard