22/05/2013

Use Capture Coordinate carefully







Use Capture Coordinate carefully

The use of the Capture Coordinate will excite the user in search of a plugin to make his life simple and quick when he wants to extract the x, y coordinates of a point because this is an easy tool to use. However, if you jump straight into it and not learn the ropes first before you go into the ring, you might face a knock-out. Observe above that by just changing the CRS from WGS84 (EPSG4326) and WGS84/Pseudor Mercator (EPSG3857) the x,y coordinate differ eventhough they both deal with WGS 84. I do not know how much that differs but I would let a surveyor clarify that for me.

20/05/2013

Win OpenStreetMap a life saver over Ubuntu OpenStreetMap

Configuring Ubuntu OpenStreetMap
Rats! No friend you
Configuring Win OpenStreetMap
Cool! OSM data gets download without hiccups
Win OpenStreetMap menyelamatkan Ubuntu OpenStreetMap

Saya tak suka mengakuinya tetapi kadangkala Win QGIS lebih handal dari Ubuntu QGIS. Tadi saya cuba muat-turun data OSM data dengan OpenStreetMap melalui Ubuntu QGIS tapi mendapat mesej  error menyatakan, saya percaya bahawa fail python berkenaan python masih belum dikemaskini lalu direboot dualboot komputer saya dan semuanya beres dengan OpenStreetMap yang terdapat pada Win QGIS. Kesimpulan: Jangan putus asa! Where there's a will, there's a way.

Win OpenStreetMap a life saver over Ubuntu OpenStreetMap

While I don't like to admit it, there are times when the Win QGIS wins over the Ubuntu QGIS. I face it here when I tried to download OSM data using OpenStreetMap via my Ubuntu QGIS but get an error message telling me I believe the appropriate python files had not been updated. So a reboot with my dualboot computer and things work out well with the OpenStreetMap in Win QGIS. Conclusion: Never give up! Where there's a will, there's a way.

11/05/2013

Windows and QGIS 1.9.0





















Windows and QGIS 1.9.0

This is a step-by-step procedure (I recommend to double-click images for a better view) to install Win QGIS using the OSGEO4W installer instead of the standalone installer. The standalone installer, once downloaded, is not dependent on live internet connection but the OSGEO4W installer is. Huh, in that case, what's so fancy about the OSGEO4W installer? Well, the latter allows the user to install specific to package so if there are packages that you seek yet unable in the standalone then you know where to look for e.g. you won't find the Topology Checker in the official Release version but the Master version. I downloaded it from here because I found OSGEO4W installer at the QGIS.org download site not updated. I am keeping a step-by-step procedure of the 1.9.0 Master version here because many QGIS users in Malaysia still use Windows however seriously, they don't know what they are missing in terms of performance until they use Ubuntu instead but that's another story.

09/05/2013

Quantum GIS Planet & Planet QGIS



Quantum GIS Planet & Planet QGIS

They sound the same but they are two specific sites with two different URL, no wonder I got lost in the cyberworld. Well, before you get lost too as I did, the first image represents the hyperlink to Quantum GIS Planet from QGIS homepage whereas if you want to know about the latest happenings (at this moment) concerning QGIS 2.0, jump to Planet QGIS.

08/05/2013

How to prepare GIS plans without a proper map?

Untick  that 'On-the-fly' projection
Import Google Hybrid as base map
Create a location map using polygon feature
Identify the study area limit by making colour fill invisible
Calculate site acerage using field calculator
Add and label road access using line feature
Add and label building types using point feature
Add supporting data e.g. firebreak
Add and distinguish tree types (Need transformed GPS data, here)
Add and distinguish soil class using polygon feature
Count by 'Points in a Polygon' module if this interest you
Bagaimanakah untuk menyediakan pelan GIS plans tanpa peta yang sewajar?

Saya masih ingat semasa mengikut ijazah, betapa sukarnya untuk memperolehi data digital. Kini data digitla amat mudah diperolehi dan dengan QGIS, perkara ini lebih mudah kerana anda boleh menyediakannya sendri. Oleh itu, artikel ini adalah khas untuk pelajar GIS yang mengalamai apa yang saya melalui dulu. Pertama, untick 'On-the-Fly' projection kerana nanti leceh apabila nak betulkan projection semua lapisan GIS bersama Google Maps. pastikan scale bar aktif untuk mengar GIS supaya syn lapisan GIS kepada scale bar. Kesemua lapisan saya disini telah diproject mengikut Google Maps kalau tidak nak cari pasal. Penentuan keluasan kawasan juga mudah akan tetapi saya mengakui masih tak tahu bagaimana nak kawal decimal points tetapi sekurang-kurang ianya adalah tepat. Kerja mengklasifikasi pelbagai jenis fitur menyeronokkan kerana ianya akan menonjolkan maklumat pada data spatial. Sudah tentu ketepatan fitur akan bergantung pada kegunaan alat GPS dan seperti telah saya buktikan dulu, data GPS mudah diterjemahkan secara spatial dengan QGIS. Amnya apa jenis maklumat yang diingini bergantun kepada apa data yang pengguna simpan dalam pangkalan data. Senarai ini tiada penghujungnya. Semua ni saya siapkan dalam tempoh kurang dari sejam tak susah asalkan ada sifu yang pandai [...seperti saya :-) ]

How to prepare GIS plans without a proper map?

I can remember when I taking my Masters, how difficult it was then to acquire digital data. Now digital data is easy to come by and with QGIS around, things are getting even more simple, you can even do it on your own. Thus, this article is especially for GIS students who face the same situation as I once went through. Firstly, I would start off by unticking the 'On-the-Fly' projection because it gets messy when I want all my GIS layers to align with Google Maps. Make sure the scale bar is activated to teach the GIS to syn the GIS layers to the scale. All my new layers would be map projected to Google Maps or else I am asking for trouble. Plot acerage is simple though I admit I still haven't learn how to limit the decimal points but at least it's precise. Classifying the various types of features is fun because it creates impressive looking spatial data. Of course, pin-point accuracy of features requires the aid of a GPS but as I have shown before GPS data can easily be spatially presented with QGIS. All-in all, it really boils down to what information the user wants to show and store in the database. The list is endless. By the way, I did all the above exercise and uploaded them here in less than 1 hour so it's really not difficult but you need a good teacher [...like me :-) ]

07/05/2013

The difference between joining layers by merge and union





Perbezaan antara menyambung lapisan mengikut  merge dan union

Lihat baik-baik sebelum anda keliru. Tahulah terdapatnya dua cara untuk menyambung lapisan: melalui merge atau union dimana kedua-dua merupakan modul Vecktor. Yang pertama terletak pada Data Management Tools/Merge Shapefiles To One manakala yang kedua terletak pada Geoprocessing Tools/Union.  Di kes pertama, attribute tables dari lapisan berbeza bersambung tapi tak berintegrasi. Di kes kedua, attribute tables dari lapisan berbeza berintegrasi terus membolehkan pertanyaan SQL. Oleh itu, gunakan Union jika hasratnya adalah untuk menjalankan SQL query yang melibatkan attribute tables dari dua lapisan. Saya masih belum tahu bilakah untuk menggunakan alternatif Merge Shapefiles To One ...kepala saya masih malas nak fikir lanjutan PRU, rasa macam cuti awam.

The difference between joining layers by merge and union

Look closely before you get yourself confused. Know that there can be two ways to join layers: by merging or unionizing them both of which are possible via Vector modules. The former uses Data Management Tools/Merge Shapefiles To One whereas the latter uses Geoprocessing Tools/Union. In the first example, attribute tables from different layers simply join each other but do not really 'merge' in the sense of the word. In the second example, attribute tables from different layers properly merge making it possible to do SQL query. Thus, use Union if the intention is to carry out an SQL query involving attribute tables from two layers. I am still trying to figure out when does one want to use the Merge Shapefiles To One alternative...my head too lazy to think because it feels like a holiday today after the General Election.



03/05/2013

Basic Statistics

SQL squery
Statistic result base on filtered output
Same result from a filtered layer
Statistics Am

Pernahkah anda memikir bagaimana untuk mendapatkan 'sum of' sesuatu dari peta, contohnya, kawasan keseluruhan fitur 'hutan'? Sekiranya anda menjangka ianya boleh dihasil melalui SQL query, fikir sekali lagi kerana Search Query Builder tidak dapat menghasilkan apa yang nak dicari. Gunakan alat sewajar untuk kerja yang spesifik kata  mekanik kereta saya dan perkara seperti sum of, mean, median dan mode terletak dalam alam statistics, maka, alat paling sesuai adalah modul Basic Statistics dibawah Vector/Analysis tools. Pada ujian pertama, Search Query Builder diguna untuk membuat carian yakni 'hutan'. Builder disini cuma memain peranan alat pertama. Dengan hasil yang masih 'hidup', Basic Statistics diaktifkan. Kini QGIS pintar dan menanda 'Use only selected features'. Modul dikonfigur dan hasil adalah seperti dicari iaitu SUM=2185.01. Pada ujian kedua, carian asal disimpan sebagai lapisan 'hutan' lalu Basic Statistics diaktifkan. Kali ini 'Use only selected features' tidak ditanda. Modul dikonfigur dan sekali lagi, hasil adalah sama iaitu SUM=2185.01. Sungguh mudah dan berkesan si modul Basic Statistic ni.

Basic Statistics

Have you wondered how to get the 'sum of' something from a map, say, the total area of all the jungle polygon features ('hutan' as in Malay language)? Well, if you think the answer is by way of SQL query, think again because the Search Query Builder will not give the actual answer you seek. Use the right tool for the right job, my car mechanic would say and here things like sum of, mean, median and mode belong to the world of statistics, thus, the right tool for this subject is the Basic Statistics module under Vector/Analysis tools. In my first test, I used the Search Query Builder to make a selection, namely, 'hutan'. Here the Builder only plays the role of initial tool. With the result still live, activate Basic Statistics. QGIS was intelligent enough to tick 'Use only selected features'. I configured the module and got the answer I needed i.e. SUM=2185.01. In the second test, the earlier selection was saved as a layer called 'hutan' then Basic Statistics was activated. This time, 'Use only selected features' did not get ticked. Configuring the module, I got the same answer I sought i.e. SUM=2185.01. Simple and effective tool this Basic Statistic module.