|True shape of an Earth|
Topography, geoids, spheroid, datum and coordinate system is a complex subject to comprehend.
From my understanding, the earth is not flat. It is round. However, the true shape of the earth is not a perfect sphere. When we view it 2D, we can define it as ellipsoid (not a perfect one I might add). When the Earth is rotating in x, y, z axis, it can be define as spheroid. Because the shape of the spheroid is so irregular, a reference ‘shell’ is applied to the original spheroid. This ‘shell’ enclosed the system and known as geoids. Geoid is the mean sea level and the true shape of the earth. Most of the calculation is used based on the geoid. The elevation of certain of all surface topography is also relative to the geoid.
|Gunung Besar Hantu|
Simple trigonometry can be use if the distance between two points is small. When involving a huge distance, the so called flat plane is becoming curve. It’s hard to imagine without a proper diagram. If you take a flat piece of paper and let it ‘touch’ a single point on a sphere. On the sphere, mark point A and B. The piece of paper is aligned 900 with the normal line, N. After that you imagine a light emit in the center of the sphere. The A and B will ‘projected’ on the piece of paper. You will immediately realize that the distance between the two points is different. Its kindda rectified. The distance becoming big. Because of the properties, the mapping of a certain area of an Earth has to sacrifice in term of distance, area and terrain feature (depending on usage). This is where aerial surveillance and satellite imagery comes to play.
To understand the nature of map projection, I am trying to further my knowledge in vector calculus, trigonometry, 3D Translation, rotational and physic. I hope one day, I will contribute something in the area of topography.
Note – For Malaysia, we used Rectified Skew Orthomorphic Map projection.
The method of projection is oblique cylindrical projection. The line of constant scales skewed at an angle to the meridian.
For the map datum, we use Kertau.
What is it used for - Everything regarding to the surface of the earth. In my case, I used it for my Herping activity. I still try to analyse the mathematics involved.
|Transformation from UTM to WGS84|
This post will be amend from time to time.