Good good study, day day up

SRTM数据中国部分终于可以下载了，盼望了几年啊。精度比GTOPO30的高多了。

ftp://edcsgs9.cr.usgs.gov/pub/data/srtm
Eurasia目录下是亚欧大陆的数据，是SRTM-3，3arc精度，大概90米。

在OZI的DEM数据格式中选择GLOBE（ARCVIEW）格式就可以打开；用MicroDEM可以对多种DEM数据进行处理。

在sourceforge上无意中留意到top download list, 看看什么软件最热门？这是前20位：

1

eMule

2

BitTorrent

google总是令人赞叹，各种出色的idea。

google计算器，不是什么技术，却给用户带来很大的方便。

我用的是MyIE，设置了google作为缺省搜索，因此只要把运算表达式在地址栏上输入，回车，结果就出来了。

SQuirreL SQL Client is a graphical Java program that will allow you to view the structure of a JDBC compliant database, browse the data in tables, issue SQL commands etc.

Jacksum is a free and platform independent utility for computing and verifying checksums, CRCs and message digests as well as timestamps of files.

Jacksum is entirely written in Java.

It supports most common checksum algorithms (Adler32, BSD sum, POSIX cksum, CRC-16, CRC-32, MD2, MD4, MD5, RIPEMD-128, RIPEMD-160, SHA-1, SHA-256, SHA-384, SHA-512, Unix System V sum, sum8, sum16, sum24, sum32, Whirlpool and xor8)

1. 下载ASTER L1B数据，AST_09(或者AST_07,未知有何区别)格式。数据包括两个文件，hdf0是15m VNIR(band 1-3)，hdf1是30m SWIR(band 4-9)，一般只需要hdf0。
2. 用MultiSpecWin打开hdf文件，将各个band分别保存为tif文件
3. 用photoshop打开三个band的tif文件，按照RGB模式通道合成为一个文件，采用231合成的效果比较好。
4. 在photoshop中对图像进行直方图调整、锐化，保存为jpg
5. 用ECW compressser将jpg转换为ecw格式
6. 在OziExplorer中校准, 投影设为UTM，然后用META FILE里面的四个点来作为校准点，分别是图像（包括黑色部分）的四个角。

今来在blog中比较关注的一个热点是社会性软件，似乎现在中文blog群体中比较活跃的一些人是做教育的，因此对这方面的探讨比较多。

对于社会学方面的东西我不大懂，对社会性软件的概念也是一知半解，不过有个软件是很令我感兴趣的：SubEthaEdit。这个软件提供了通过网络多人共同进行文本编辑的功能，从screenshot上看，有点象IM聊天的多个参与者，共同对文件进行修改，通过不同颜色可以区别出不同人改动的部分。

软件的说明中提及了此软件可以用于pair programming，我想如果这样的软件真的能够达到实用化的话，基于网络的远程PP也是有可能的。即使不是远程PP，对于工作小组内部的商讨事情也会带来很大的方便。

可惜软件是用于Mac OS X的，没有办法试用。

交流真是工作中非常重要的一部分，想想每天多少人在天空飞来飞去，就是为了参加半天的会议，能有一次见面交流的机会。电话、网络等等各种先进科技，目前都还是未能让人们能自如的交流，提供真切的体验。这是一个极具潜力的领域。

EE times 的一篇文章介绍了Garmin GPS map76s的内部模块结构，下图是引自该文章的。

据分析，这样一个GPS的成本价不足100美圆，可是现在市场价是差不多400美圆！好赚吧？:)

从照片中可以看到，四螺旋天线垂直安装在顶部，因此GPS在直立放置时的信号接收效果是最好的。

在玩户外的人中，GPS的拥有量开始增加，什么型号的GPS适合户外使用？我在买GPS之前看过不少资料，可以参考一下。

GPS information是一个很值得看的站点，几大GPS厂家的设备信息、GPS相关软件、使用心得等等资料非常齐全。

该网站里面一篇文章Important features for a hiking GPS介绍了什么GPS适合于hiking使用。

摘录部分出来：

Below are my “essential hiking feature list” of GPS receiver features.

(I omitted features that are present in ALL receivers.)

1. 12 channel parallel receiver system: Needed for best reception in difficult terrain and tree cover.

2. WaterProofness: Unit should be rated submersible to protect it from getting wet.

3. Long battery life: Keeps you from having to carry so many batteries.

4. Built in Maps: Not absolutely essential, but big help in orientation and estimating distance to nearest roads.

5. Route capability: Twenty Route capability is pretty standard. Make sure you get one with at least 20 routes.

6. Waypoints: 500+ user entered waypoints are pretty standard. Make sure you get one of these.

7. Multiple Datum capability is pretty standard: Make sure all the datums you will want to use are included in the GPS you select.

8. Fit nicely in your pocket and lightweight: This is a very personal thing, but you should consider it when you are thinking about hauling a unit around in the wilderness.

9. Bearing to next waypoint: Almost universal, but essential to hiking use.

10. Screen Size and your ability to read it are important especially if you have problems with viewing fine detail.

Not ABSOLUTELY essential features, but nice to have.

1. “Map” screen (as opposed to just a numerical lon/lat position fix): Makes it much easier to see where you are relative to reference waypoints.

2. Rotatable screen: Garmin makes a couple of units capable of rotating the screen vertical (handheld use) or horizontal (car dash use). These are not the handiest for pocket use, but lots of people like this compromise for joint hiking/car use.

3. UTM readout may be a consideration for some. This feature is available on a limited selection of consumer GPS receivers.

4. Topo Maps uploaded into your GPS: The Garmin USA Topo CD maps contain contour lines and small stream data very helpful in navigating in off-road territory. Magellan has a new TOPO map offering for the M330 available late Summer 2001.

5. For use under heavy tree cover or difficult (multipath) terrain conditions, an external amplified antenna will generally be helpful.

6. A minimum of 8 megs of map memory is recommended on a mapping GPS though you can “get by” with 1.4 megs or so.

MySQL的数据表访问锁定：读操作、写操作分别要申请读锁和写锁，读锁可以并发，写锁是唯一的。通过配置或者一些命令可以改变读、写的优先级。在MySQL手册中关于性能部分有说明。

普通的表类型，如MyISAM表是采用table级锁定；InnoDB和BDB是支持transaction的表类型，它们采用更小粒度的锁定，BDB是page级锁定，InnoDB是row级锁定。