Equipment Donation to RUA
The Royal University of Agriculture’s department of Land Management and Land Administration, were the recipients of 3 complete sets of GNSS survey equipment, donated by Trimble and Aruna Technology. The equipment will allow the extension of teaching to include current GNSS survey techniques, in addition to the optical survey techniques currently taught at the department. Present at the hand over ceremony, pictured below are Paul Gager, Technical Director at Aruna Technology, Vung Setha , Dean of the department of Land Management and Land Administration and a class of enthusiastic students studying at the undergraduate level.
Kamchay Hydropower Project – May 2012
This image shows the extent of the reservoir of the recently completed Kamchay hydropower project. The image is from the dry season 2012 (May) so the reservoir is not yet at full capacity. Expected maximum water level is 175m, somewhere between the 160 and 180m contours shown in this map.Note that there are some inaccuracies in the contour data due to the limitations of the data (from 1:100,000 scale topographic maps).
Kamchay Hydropower Project
Bokor Mountain Development
Interesting satellite image showing the extent of the Bokor Mountain development in Cambodia, which is still under construction.
Bokor Mountain Development (click to enlarge)
Topology 101 for ArcGIS 10
There still exists some confusion about how we can work with topology in ArcGIS since workstation ArcINFO was discontinued some years back. So as a quick refresher, here is how we can work with topology in ArcGIS.
នៅតែមានការយល់ច្រឡំអំពីរៀបធ្វើការជាមួយ topology នៅក្នុងកម្មវិធី ArcGIS តាំងតែកម្មវិធី ArcInfo ផ្អាក់ការផលិតជាច្រើនឆ្នាំមក ហើយ។ ដូចជាមានការបង្កើតឡើង នូវកម្មវិធី topology នេះជារបៀបដែលយើងអាចធ្វើការជាមួយនិង topology កម្មវិធី ArcGIS ។
What is Topology ?
តើ Topology គឺជាអ្វី?
In geodatabases, topology is the arrangement that defines how point, line, and polygon features share coincident geometry. For example, street centerlines and census blocks share common geometry, and adjacent soil polygons share their common boundaries.
នៅក្នុង geodatabases, កម្មវិធី topology គឺជាអ្នករៀបចំនឹងកំណត់អោយបានច្បាស់លាស់នូវ point, line និង polygon ដែលកើតមានឡើងតំណាល់គ្នាតែម្តង។ ឧទាហរណ៌ ដូចជាចំណុចកណ្តាលនៃទ្រូងផ្លូវ និងទិន្ន័យអំពីប្រជាជនទៅ តាមតំបន់និមួយៗ ហើយនិងធ្វើការរៀបចំដីថ្លីរបស់ពួកគេទៅតាមព្រំប្រទល់ដី។
To create a with a topology, you will need at a minimum:
ការបង្កើត topology អ្នកត្រូវការកម្មវិធីដូចជា:
- ArcGIS Desktop Standard or Advanced Software (fomerly ArcEditor and ArcInfo)
- កម្មវិធី ArcGIS Desktop Standard ឬ Advanced (ArcEditor និង ArcInfo)
- A multi-user Geodatabase. You can start with SQLServer Express (Free)
- ការប្រើប្រាសច្រើនក្នុងពេលតែមួយ អ្នកអាចប្រើជាមួយកម្មវិធី SQLServer Express
- A feature dataset containing in the Geodatabase one or more feature classes
- ក្នុង feature dataset និមួយៗ ដែលមាន feature classes មួយ ឫក៌ច្រើននៅក្នុង Geodatabase
- If you already have some data whose topology needs to be checked, you should load that data into the feature dataset to create a new feature class. A feature dataset is basically a container, holding one or more feature classes. One feature class would normally represent one kind of thematic feature, e.g. soil polygons, road lines etc.បើសិនជាអ្នកមានទិន្ន័យខ្លះ ដែលត្រូវការពិនិត្យក្នុង topology អ្នកត្រូវតែដាក់បញ្ចូលវាទៅក្នុង feature dataset ដែលបានបង្កើត feature class ថ្មី ។ feature dataset ជាកន្លែងផ្ទុកដំបូងគេ ជាចំណែកមួយ ឬច្រើននៃ feature classes ។ Feature class មួយតំណាងអោយមួយប្រភេទនៃ thematic feature ។ ឧទាហរណ៌ ដូចជាទ្រង់ទ្រាយដី និងរូបរាងផ្លូវ ។
- Once you have a feature class loaded, you need to define a topology rule using ArcCatalog. Topology rules define the permissible spatial relationships between features. e.g. “Must not overlap” and are stored in the feature dataset. You also need to specify which feature class or classes the topology rule applies to.ពេលដែលអ្នកបញ្ចូល feature class អ្នកត្រូវធ្វើវាទៅច្បាប់របស់ topology ដោយប្រើកម្មវិធី ArcCatalog ។ ច្បាប់របស់ Topology ត្រូវអោយបង្ហាញអោយបានច្បាស់រវាងទំនាក់ទំនងរបស់ features ។ ឧទារណ៌ មិនអនុញ្ញាតអោយត្រួតស៊ី “Must not overlap” និងរក្សានៅក្នុង feature dataset ។ អ្នកត្រូវបញ្ចាក់អោយច្បាស់លាសទៅលើ feature class ណាមួយ ឬទៅលើប្រភេទរបស់ topology ដែលបានកំណត់ ។
- The next step is to validate the topology, which checks all features to see if they meet the topology rules. You can validate topology in ArcMap (while editing) or in ArcCatalog.ជំហានបន្ទាប់គឺការវាយតម្លៃរបស់ topology, ត្រួតពិនិត្យរាល់ features ថាតើគោរពទៅតាមច្បាប់របស់ topology ឬក៌អត់។ អ្នកអាចធ្វើការវាយតម្លៃ topology ក្នុងកម្មវិធី ArcMap (អំឡុងពេលដែលកំពុងប្រើប្រាស់វា) ឬ ArcCatalog ។
- Correcting the errors can be done one by one in ArcMap using the error inspector. You can right-click the error in the list or on the map and click one of the available fixes. The fixes listed depend on the type of error.ធ្វើការកែរកំហុសអោយបានត្រឹមត្រូវម្តងមួយៗ នៅក្នុងកម្មវិធី ArcMap ដោយប្រើប្រាស់ឧបករណ៌ error inspector ។ អ្នកអាចចុច Mouse ខាងស្តាំ ទៅលើកន្លែងដែលមានកំហុសក្នុងតារាង ឬនៅលើផែនទី និងចុចមួយដងទៅលើឧបករណ៌ជួសជុល ។ ការជួសជុលអាស្រ័យទៅលើប្រភេទដែលមានកំហុស ។
Topology Example (c) ESRI
You can read more about creating and managing database topologies here;
អ្នកអាចអានបន្ថែមទៀតអំពីរបៀបនៃការបង្កើត និងរបៀបនៃការរៀបចំទិន្ន័យនៅក្នុង topologies នៅទីនេះ ។
For more advanced users, it is also possible to automate some topology fixes using geopreocessing tools and Model Builder in ArcMap. e.g.
សម្រាប់ការប្រើប្រាសដែលមានកំរិតខ្ពស់ វាជាភាពងាយស្រួលដោយស្វ័យប្រវត្តិខ្លួនឯងខ្លះៗទៅលើការជួសជុល topology ដោយប្រើប្រាស geopreocessing និង Model Builder ក្នុងកម្មវិធី ArcMap ។
Monthly Cloud Cover Data in Cambodia
These statistics are calculated from daily satellite observations and are useful for planning imagery acquisition.December to February are clearly the best months, but it is interesting to note that the late wet season (Nov) is better than April-May, though of course flood waters are still up in November.
Average Cloud Cover Cambodia
SPOT6 Satellite – First Pictures
Three days after being orbited, SPOT 6 has delivered its first images
Astrium Services has posted the first images from the SPOT 6 satellite, just three days after its launch on 9 September.
SPOT 6 will assure continuity of data from the series of satellites operating since 1986, along with many technological innovations. Its unique responsiveness and acquisition capacity are set to benefit a broad spectrum of operational applications.
These first images present very varied landscapes, highlighting SPOT 6’s potential for applications like urban and natural resource mapping or agricultural and environmental monitoring. The wide imaging swath (60km), identical to that of the other SPOT satellites, makes SPOT 6 an ideal tool for covering vast territories, while its 1.5m resolution – against 2.5m on SPOT 5 – enables it to distinguish smaller features than ever before.
To post the images, all operational systems swung smoothly into action, from satellite tasking to image acquisition, reception and processing.
In January 2014, the arrival of SPOT 7 will bring more new services including daily revisits. Together, the SPOT 6 and SPOT 7 constellation will assure continued availability of high-resolution, wide-area products through to 2024.
Bora Bora (c) Astrium Geoinformation Services
Bora Bora Detail
Land Concession Monitoring – From Space
With the advent of newer earth imaging satellites with daily overpass and capture possibilities, it is now even easier to monitor land use change. For example, we can examine the history of development of two Economic Land Concessions (ELCs) inside the Beng Per Wildlife Sanctuary. The concessions were granted in early 2010 and by March 2011, land clearing was well advanced.
Clearing of Land Concessions as of March 2011
If we examine the historical imagery, we can see the incremental clearing that has occurred over 1 year.
Historical Imagery: Mar-2010 -> Oct-2010 -> Mar -> 2011
SPOT vs. SRTM DEM Comparison
Well I’ve finally manged to get my hands on some SPOT DEM data for Cambodia for a project in the Southern Cardamoms. Quite an improvement over the SRTM (90m) data. The SPOT DEM has a resolution of 30m at the equator. From Astrium:
A SPOT DEM is a digital elevation model produced by automatic correlation of stereopairs acquired by the HRS instrument on SPOT 5.
Unlike a digital terrain model (DTM), which describes the distribution of terrain or “bare earth” heights, a DEM includes “first surface” elevations including vegetation and man-made structures.
SRTM DEM Detail. Scale approx 1:75,000
SPOT DEM Detail. Scale Approx. 1:75,000
For more info see http://www.astrium-geo.com/en/2790-elevation30-dem-spot-dem or please Contact Us
Dispelling Myths about Garmin GPS Accuracy
The declaration of the accuracy by Garmin GPS receivers often leads to confusion. What does it mean if the receiver states an accuracy of 4 m? This readout refers to the so-called 50 % CEP (Circular Error Probable). This means that 50 % of all measurements are within a radius of 4 m. On the other hand, 50 % of all measured positions are outside of this radius. Furthermore, 95 % of all measured positions are within a circle of twice this radius and 98.9 % of all positions are within a circle of 2.55 the radius. In the given example, nearly all positions are within circle with a radius of 10 m. The determined position is in the worst case accurate to 10 m.
GPS Error Plot
Source : http://www.kowoma.de/en/gps/accuracy.htm
Setting Up a Garmin GPS to Use Indian Datum
We often get asked about this question, so here are the full instructions on how this can be done:
Topographic maps in Cambodia use one of two datums; Indian 1954 and Indian 1960. By default, your Garmin GPS unit is set up to WGS84 datum, which is about 500m different to the Indian datums. If you want to display coordinates using one of the Indian datums, do the following;
- In your unit, go to SETUP and then UNITS
- Go to MAP DATUM and press the ENTER button
- Garmin supports the ‘Indian Thailand’ datum which is close to, but not exactly the same as the other INDIAN datums. The differences are:
INDIAN 54 vs. INDIAN Thailand: 2.2 meters
INDIAN 60 vs. INDIAN Thailand: 6.4 meters
Remember that standard GPS is generally accurate to about 10m, so these differences may be insignificant to you. If you want to be more precise, you can select the USER datum and enter the following parameters.
|DX||+ 217||DX||+ 198|
|DY||+ 823||DY||+ 881|
|DZ||+ 299||DZ||+ 317|
|DA||+ 861||DA||+ 861|
|DF||+ 0.28361370||DF||+ 0.28361370|
In Cambodia, the old 1:50,000 scale topographic maps are based on the INDIAN 1960 datum. The newer 1:100,000 scale maps from the Reconnaissance Survey Project (the “JICA Maps”) from 1998-2002 are based on the INDIAN 1954 Datum.
ផែនទីភូមិសាស្ដ្រមួយប្រើប្រាស់ក្នុងកម្ពុជានូវដាតូមពីរ ដូចជា ឥណ្ឌា ១៩៥៤ និង ឥណ្ឌា ១៩៦០ ។ ផែនទីចាស់មានមាត្រដ្ឋាន មូលដ្ឋានគ្រឹះខ្នាត ១:៥០,០០០ ដោយមានដាតូម ឥណ្ឌា ១៩៥៤ ។ ថ្មីៗ មាន ផែនទី ខ្នាត ១:១០០,០០០ ពី គំរោងអង្កេតការណ៍ ដែលជាគ្រឹះមានដាតូម ឥណ្ឌា ១៩៦០។
ដោយតម្រូវការរបស់ Garmin GPS ត្រូវមានខ្នាតចំពោះដាតូម WGS84 ជាមួយអំពីភាពខុស គ្នា ៥០០ម៉ែត្រ នៃដាតូមឥណ្ឌា ។ បើសិនលោកអ្នកចង់បង្ហាញនូវកូអរដោនេមួយ ដោយមានការប្រើ ប្រាស់ ដាតូមឥណ្ឌា ត្រូវអនុវត្ដតាមដូចខាងក្រោម ៖
1- ក្នុងខ្នាតរបស់វា ត្រូវចូលទៅពាក្យ SETUP និងបន្ទាប់មក UNITS
2- ចូលទៅ MAP DATUM និង ចុចលើ ENTER ឧបករណ៍ ប៉ូតុង
3- ជំនួយ Garmin វាមានដាតូម ឥណ្ឌាថៃឡង់ដិ៍ជាទៅចុងបញ្ចប់ ប៉ុន្ដែមិនសូវច្បាស់ លាស់ ដូចដាតូម ឥណ្ឌាដ៍ទៃទៀតទេ។ ភាពខុសគ្នាគឺ ៖
ឥណ្ឌា ៥៤ ជំនាន់ ខុសគ្នានឹង ឥណ្ឌាងៃឡង់ដិ៍ ៖ ២,២ ម៉ែត្រ
ឥណ្ឌា ៦០ ជំនាន់ ខុសគ្នានឹង ឥណ្ឌាងៃឡង់ដិ៍ ៖ ៦,៤ ម៉ែត្រ
ចូលចំណាំ ធម្មតា ស្ដង់ដារបស់ GPS ដែលមានតំលៃទៀងទាត់ប្រមាណ ១០ ម៉ែត្រ ដូនេះ ការខុសគ្នាប្រហែលមិនសំខាន់ ចំពោះអ្នក ។ បើសិនជាអ្នក ចង់បានភាពលំអិត ជាក់លាក់ លោកអ្នកអាចជ្រើសរើស ដាតូមប្រើប្រាស់ និង យល់ព្រមតាមកំណត់ដូច ខាង ក្រោម ៖
|DX||+ 217||DX||+ 198|
|DY||+ 823||DY||+ 881|
|DZ||+ 299||DZ||+ 317|
|DA||+ 861||DA||+ 861|
|DF||+ 0.28361370||DF||+ 0.28361370|
4- ដើមី្បប្រៀបផ្ទឺម ផែនទីភូមិសាស្ដ្រ ទំរង់ទីតាំង តម្រូវឱ្យយដាក់ ’UTM UPS’ ក្នុង Garmin GPS
Historical Maps of Phnom Penh
Aerial Photo Around Central Market, 1943
These images are from a report entitled “Phnom Penh développement urbain et patrimoine” or “Phnom Penh, Urban Development and Heritage”.
Urban Expansion 1958 to 1968
Phnom Penh Urban Plan Map, Undated
Phnom Penh Urban Expansion 1890 to 1958
Phnom Penh Urban Expansion 1890 to 1994 cont..
Urban Plan 1903
Urban Plan 1922
Urban Plan 1937Plan des casiers, 1930
Satellite Image of Kamchay Hydropower Project
This high resolution satellite image is of the Kamchay Hydropower in Kampot province Cambodia. The project is located inside Bokor National Park. The new road to the top of Bokor Mountain is visible in the bottom left hand corner. Kampot town is visible in the bottom right corner.
Aruna Technology are authorized distributors for satellite imagery from GeoEye, SPOT and RapidEye. Please Contact Us for more information.
Satellite Image of Kamchay Hydropower Project, 2012
River Bank Erosion Opposite Diamond Island
Don’t buy land in this area !
Bank Erosion 2003 - 2010
Around the corner on the Mekong Side
Using Feature Templates in ArcGIS
1. Create a new shapefile in ArcCatalog and set the coordinate system. In this example, I have created a polygon shapefile called landuse_2012.shp
2. Add the feature class landuse_2012.shp to ArcMap and open the attribute table. Notice that it has no features.
3. Add a field called LU_CODE with type Short integer
4. Add a field called LU_TYPE with type Text and Length 35
5. Delete the field called ID that was added by ArcGIS.
6. In the Table of Contents, right click on the layer and choose Properties -> Symbology
7. Change the symbology to Categories and the Field to LU_TYPE
8. Click the Add Values button, then enter the description of the first class, e.g. Forest
9. Then click Add to List
10. Change the Symbol to the desired color e.g. Green
11. Then repeat the process, adding new classes called “Water” and “Farmland”, for example
12. Click Ok to close the layer properties
13. Zoom to the area where you are digitizing new features
14. Make the Editor Toolbar visible and choose Editor -> Start Editing
15. Notice that in the Create Features window, the three classes are displayed
16. Now click the Organize Templates button
17. Select Farmland and click Properties
18. Set the LU_CODE field to 3
19. Click Ok and repeat the process for Water (LU_CODE = 2) and Forest (LU_CODE = 1).
20. In the Create Features window, select Farmland and in the Construction Tools window, select Polygon
21. Now draw a farmland polygon as desired
22. Create a single feature for each class. You will need to change the class in the Create Features Window to switch classes.
23. Stop editing and open the attribute table.
24. Notice that all features are fully attributed.
Free Satellite Imagery of Cambodia
Recent announcement from USGS:
OrbView-3 satellite images collected around the world between 2003 and 2007 by Orbital Imaging Corporation (now GeoEye) at up to one-meter resolution can now be downloaded at no cost through USGS EarthExplorer.
“This is a significant addition to the USGS archive and a valuable resource for the global science community,” said Matthew Larsen, Associate Director, Climate and Land Use Change. “Free access through the USGS archive amplifies the utility of the data, making it feasible for many researchers to study large areas at this level of accuracy.”
I took a quick peek at what is available for Cambodia (see graphic below). Would be nice to have more I suppose, but hey, better than nothing.
Orbview-3 Coverage Available for Cambodia
The Royal University of Agriculture’s department of Land Management and Land Administration, were the recipients of 3 complete sets of GNSS survey equipment, donated by Trimble and Aruna Technology. The equipment will allow the extension of teaching to include current GNSS survey techniques, in addition to the optical survey techniques currently taught at the department. more »
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This image shows the extent of the reservoir of the recently completed Kamchay hydropower project. The image is from the ...
Interesting satellite image showing the extent of the Bokor Mountain development in Cambodia, which is still under construction.[caption id="attachment_803" align="aligncenter" ...