# [FOSS-GPS] Program to create survey-like map?

Jochen Peters jochen.peters at uni-duesseldorf.de
Tue Aug 25 13:21:06 PDT 2020

```Hi John,

Try to figure out how to create bitmap (bmp) files with python and then draw points and lines there. Then you can use very little mathematics to display the region you want to represent on e.g. 1000x1000 pixels.  For example, Europe goes from lon -10.0 to +25.0 and from lat 35.0 to 70.0. You can then scale 35 degrees in x and y direction to 1000 pixels. If your region is only limited to about 50m, then this projection is not so faulty.

foxtrotgps can only load a single route and display it on a map - so it's nothing for e.g. displaying the outlines of several buildings. I have made the experience that many OSM and map tools can do too much and overstrain you or don't have the exact function you need.

Here is a small c++ code example (and an image as attachment, where I used this lat/lon projection to x,y):

// europa: lon  -10..25
//         lat   35..70

#define LAT_BOUND_START  35.0
#define LON_BOUND_START -10.0
#define LAT_BOUND_DIF 35.0
#define LON_BOUND_DIF 35.0

#define IMAGE_WIDTH         8000
#define IMAGE_HEIGHT        8000

...

void drawFunc(double lon, double lat) {
int x,y;
lon = lon - LON_BOUND_START; // this maps -10.0 to 0.0
lat = lat - LAT_BOUND_START;
x = IMAGE_WIDTH*(lon/LON_BOUND_DIF);
y = IMAGE_HEIGHT - IMAGE_HEIGHT*(lat/LAT_BOUND_DIF);
placePixel(x,y,WHITE);
}

Am Mon, 24 Aug 2020 16:29:06 -0400
schrieb John Ackermann N8UR <jra at febo.com>:

> Thanks, Jochen!
>
> I am not familiar with foxtrotgps but will look at it.  I think it
> may be overkill for my needs but maybe not.  One thing is that I'm
> talking about small distances -- spacing of <50 meters between
> points, usually.
>
> I probably have the Python code available to fairly easily read a
> list of lat/lon and calculate distance/bearing between each pair.
> What I don't have is the knowledge to then plot that onto a sheet to
> a sheet to create what looks like a survey map with boundaries and
> markers.
>
> John
> ----
>
> On 8/24/20 3:16 PM, Jochen Peters wrote:
...
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