Interesting algorithmic problem

[schajee]

Hi,

I have a list of real numbers. They are actually coordinates of a map, the points which when joined will create a polygon of the shape of a particular area.

Now I got these points from AutoCAD Map something and the difference between two points is very small. e.g. 72.9444 and 72.9429 i.e. the scale of the map was very small.

What I want to do now is to increase the scale of the maps, i.e. increase the points difference so that the polygon that is generated is large compared to the one that is generated when I use the original coordinates. e.g. the new points should be something like 72.9444 and 82.9429 or something.

I don't exactly know how to proceed with this problem to increase the size of the polygon, but any help in this regard would be great.

[xgoat]

There are two stages that I would go through to do this:

1) Find the top left-hand point co-ordinates (i presume that the co-ords are from the top left - if they're not then find the relevant corner's co-ordinates). Subtract the co-ordinates from the polygon points, i.e. subtract corner x from x and corner y from y. Do this for ALL points within view.

2) Next you magnify the points so that there is a larger difference between them, e.g:

new coords = (x,y) * zoom

You can alter the value of zoom to whatever you like - if you set it to 1 then the result will be the same as you started with. If you set it below 1 then you will zoom out. If you set it above 1 then you will zoom in.

Remove points that are not in the visible area - ones that aren't will be below 0 in the x or y co-ord shouldn't be displayed. Points above the highest value of the visible area should be removed too.

O yea - if you want to find out the size of the visible area then:

if you know the original size of the area then just multiply it by the zoom.

Hope this helps.

[schajee]

That's something what I've been trying to do but it just doesn't seem to increase the scale to a level that would look better.

What you said by locating the top left corner and subtrcting that from all x and y, that would mean I subtract 0,0 from all x,y because from top left corner is 0,0. I don't get that point.

Besides what I tried to do was I subtracted 72 from all x's as they all has 72.something values, so I was left with 0.something values. Next I multiplied that by 100 to increase the scale. I did the same with y's by subtracting 32 and multiplying by 100.

Now logically that seems fine but the scale is still not big enough. e.g. I had some points like this:

X: 72.9444, Y: 33.7070
X: 72.9429, Y: 33.7064
X: 72.9414, Y: 33.7062
X: 72.9396, Y: 33.7059
X: 72.9384, Y: 33.7059
X: 72.9372, Y: 33.7056
X: 72.9359, Y: 33.7053
X: 72.9345, Y: 33.7047
X: 72.9319, Y: 33.7033
X: 72.9299, Y: 33.7017

Now as you can very well see even when I do all the maths, I end up with numbers like this:

Points: 94.44
Points: 94.29
Points: 94.14
Points: 93.96
Points: 93.84
Points: 93.72
Points: 93.59
Points: 93.45
Points: 93.19
Points: 92.99

Now I cannot multiply the orginal numbers by 1000 because that would result in the points being way outside the size of the image and all I'll get would be a nice big box filled with some color.

Plus I don't think I'll be able to use these points to draw a polygon because ImageFilledPolygon only takes integers as input. This also hampers my progress as I end up at square one with a point difference that does not matter when I reduce the numbers to integers.

Robert wrote:

There are two stages that I would go through to do this:

1) Find the top left-hand point co-ordinates (i presume that the co-ords are from the top left - if they're not then find the relevant corner's co-ordinates). Subtract the co-ordinates from the polygon points, i.e. subtract corner x from x and corner y from y. Do this for ALL points within view.

2) Next you magnify the points so that there is a larger difference between them, e.g:

new coords = (x,y) * zoom

You can alter the value of zoom to whatever you like - if you set it to 1 then the result will be the same as you started with. If you set it below 1 then you will zoom out. If you set it above 1 then you will zoom in.

Remove points that are not in the visible area - ones that aren't will be below 0 in the x or y co-ord shouldn't be displayed. Points above the highest value of the visible area should be removed too.

O yea - if you want to find out the size of the visible area then:

if you know the original ....