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I am from a computer science background and I would say I have zero experience with GIS software and terminology. Can anyone confirm if I can use QGIS for the following problem:

  • I used a motion capture system to collect the movements of people in a room.

  • The system I used has its own coordinate system where the center of the room is (0,0)

  • The collected data is in the form:

    timestamp, id, x, y
    e.g. 1/27/2018 7:26:17 PM, user1, -1.62, 1.71
    

Where x and y represent the position with reference to the room center in meters. Look at the sketch:

enter image description here

So as now I have a list of points of the person movement, I want to create a heatmap of that. I used QGIS to import my data and I was able to create a heatmap but I have to zoom in to see a better view. I think this is related to CRS. Can I change the coordinate system to have (0,0) is the center of the view? and the total view box is 10 by 6 meters?

enter image description here

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    If you wanted to use your data as 'QGIS/GIS' data, it would have to reference real world coordinates relative to the actual 0,0 center of the WGS84 coordinate system. You could in theory "move" all your points to a known location, thus giving them proper "GIS" coordinates... right now QGIS thinks your data is in EPSG:4326, in which 0,0 is the start point (near the coast of Africa, in 'real world' space). Commented Sep 25, 2020 at 20:18
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    In my opinion, it is enough to simply change the projection to any Projected Coordinate system (for example, WGS 84 / UTM zone 42N EPSG: 32642). This can be done in the layer settings. Commented Oct 28, 2020 at 8:00

2 Answers 2

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You might want custom CRS that matches your room or a generic room. A custom Oblique Mercator projection, https://proj.org/operations/projections/omerc.html, centered on your origin point and rotated to match your room axes might be what you need. The Oblique Mercator is accurate within 15 degrees (1600km) of your centerline.

If you want to geolocate your room, determine the geographical coordinates of your chosen origin and the rotation of the axis clockwise from north. You could choose an arbitrary point, use a GPS and Compass, or use QGIS and a basemap. Below, I used QGIS and an OSM basemap to locate a football field, and eyeballed a center point, and eyeballed the map rotation as 54 degrees (see the adjustable Rotation box on the bottom margin)

Then:

  1. Open Settings/Custom Projections

  2. Choose the green '+' to add a CRS

  3. Enter a Name: "MyFootballField"

  4. Enter the Format: "Proj String (Legacy -- not recommended)"

  5. Enter Parameters like these with the center longitude lonc and latitude lat_0, and the rotation clockwise from north as +alpha:

    +proj=omerc +lat_0=37.204392 +lonc=-76.497682 +alpha=-55 +gamma=0 +x_0=0 +y_0=0 +ellps=WGS84 +units=m +no_defs

You could toggle the Format field to translate it into WKT, but I found the proj4 is easier to define and edit.

The details of the other settings in proj4 format are at https://proj.org/operations/projections/omerc.html

enter image description here

Then, if you can choose this as project CRS, import your data, and do your analysis in your local CRS.

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Alternatively you could create a custom CRS in QGIS. This post can be helpful: Creating custom CRS in QGIS

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